Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: bobster on September 26, 2018, 11:46:06 AM

Title: HH IC100 overheating BD711 transistor...help !
Post by: bobster on September 26, 2018, 11:46:06 AM
hi guys , new-ish member here with a recently purchased HH IC100 amp circa 74 -75.
Amp has been working fine for long periods and is out of the shell just now for a clean and visual inspection.

The power amp board is AO3103/7 variant with two [driver i think?] heatsinked transistors numbered BD711 [ uppermost] and BD712.
Earlier on i tried a treble booster through the amp at low volume and saw smoke from the power board and amp stopped working.

Fuses all ok but noticed R26 [ 10 k ] and R10 [ 100r ] looking burnt so replaced them and amp is now working again.

However , the transistor near these resistors numbered BD711 is getting really hot even after just a short time of playing.........it's lower twin BD712 is very cool in comparison.

Can anyone with experience of these amps advise what the problem may be ?
many thanks !
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: Enzo on September 26, 2018, 12:02:16 PM
Can you post or link a schematic?
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on September 26, 2018, 04:52:30 PM
Hi Enzo , thanks for coming in
i don't have the schematic for this amp but there is another similar amp made by the same company as follows http://oi197.photobucket.com/albums/aa211/bajaman002/HHVSMusicianamplifier1of2.jpg       

i think there will be differences between both but perhaps similar topology which may give some clues?

I could go ahead and replace the BD711 i suppose but from what i read online there could be other things at play causing these problems elsewhere in the circuit.
im usually a vintage valve amp non master volume guy so the SS stuff is a bit daunting for me.

fwiw the amp all works and gives very healthy and clear output....
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on September 28, 2018, 02:44:18 PM
I'm attaching that schematic as the pdf version is easier to enlarge.
The topology may be similar, but your component designators are meaningless without the correct schematic.
So tell us which resistors on this schematic you think would correspond to the ones that burnt.
Agree with you that the BD711 & BD712 should be similar in working temperature.

You might want to consider buying a schematic from MAJ:  http://www.majelectronic.co.uk/
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 01, 2018, 07:53:25 AM
Hi there , thanks for this.
The resistors i 'think' may apply on the VS schematic you attached are r16 r17 and r24.....
[obviously the topology is not the same as the VS schem attached has a different power board variant than my older IC100 model.]

for further info - on the IC100 I tested all the 741 opamps and get 15v and tested the main filter caps / 2n3440 / 2n5415 / BD711 / BD712 [ on power amp board ] and get 47.2v dc.

A point to make is that i was testing the chassis through an 8 ohm cab and when i played hard without a booster another resistor smoked [ 33 ohm ] .  [ r29 on my IC100 board and possibly R24 on the VS musician board ]

The actual combo cab appears to be factory wired for 16 ohms so i used that to test again once i replaced the 33 ohm and it seemed to behave ok with no more smoke possibly due to less power / current being drawn?    Bd711 still heating though
   lovely amp , amazing vibrato and a nice contrast to my VS musician head,
Title: HH IC100 schematics
Post by: vintagekiki on October 05, 2018, 06:13:36 PM
http://www.tube-town.de/ttforum/index.php?action=dlattach;topic=21045.0;attach=49439
HH IC100L

https://www.dropbox.com/s/bxuobgpiv2qizlj/IC100.pdf
HH IC100
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 05, 2018, 09:45:48 PM
Going by the symptoms and using the HH IC100 schematic that *Vintagekiki* kindly posted,  :dbtu:

If R10 has burnt out then something maybe wrong around Q2. Burnt resistors means too much current is flowing.
Q2 is the VAS (Voltage Amp stage) which drives the outputs. bias is set by R15,R35 and D3.
R15 is *AOT* (which means Adjust on test) bias may have drifted.
D3 might be mounted on the Heatsink.

Before you go much further a couple of points,
With no speaker connected check the DC voltage at the speaker terminals, it should be less that 500mV,, closer to Zero is better.

As this Amp is likely a head cab then be aware that the speaker negitive is NOT Ground. If the speaker neg is accidentally grounded back to circuit ground it will overheat.

These circuits have 2 feedbacks, voltage and current FB.
R32 forms part of the Current FB.
Check that the speaker output sockets on the chassis are not connecting to chassis.
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 06, 2018, 08:35:34 AM
Hi Phil and Kiki , many thanks for your input and especially for the schemos which i will try and study.
[ i'm mainly a vintage valve amp guy so the SS stuff is still a bit of a 'dark art' lol ]

I tested the speaker outs and got a reading of zero so hopefully good there....

I searched online and noticed that the BD711 transistor that is heating has an equivalent BD911 which seems to be a higher spec in terms of wattage and voltage capacity.      I may buy a BD911 and BD912 and replace that pair for insurance but that may of course leave an untraced fault elsewhere....so will check around Q2 also as you say

For now while i try to make sense of the circuit i will run the amp with a fan on back to cool and stick to 16 ohm cabinets as that may draw less power / current and maybe keep the amp in a safer zone.

Something that may be implicated is that the main filter caps are 4700uf / 50v and are original. Their vent holes are letting a little bit of dried up powdery stuff through so they look to be heading towards expiry.
I wonder if replacing them with new ones at 63v will make a difference to the fault?
It certainly won't do any harm so i will order a pair asap...
thanks again guys
rob          [ p.s. don't know why the past couple of paragraphs have lines through them ! ]
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 06, 2018, 02:14:57 PM
The design is for TIP29C and TIP30C drivers so the BD parts are overkill for either the 711 or 911 series. 
Use whatever is most available and cheap for your location.  TIP series are usually very cheap and common, BD types may be more common in Europe.
R26 is the base to emitter resistor for the upper driver, so likely the bad part that is overheating (BD711) got damaged along with R26.
Suggest you replace upper and lower driver, then do DC voltage checks with no load connected.
Post your DC voltages for E,B,& C of both drivers after replacement.  Also for output transistors and mV DC across each of R34 and R28 (0R33 6W).
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 06, 2018, 02:53:22 PM
thanks G1 ,  will be a few days till i get around to it [ kids waiting on parts etc ] but will get back with some results...

can i take it that when you advise replacing the two driver transistors you mean the Tip29 and 30 [ bd711    / 712 ] ?   or are you referring to the other two transistors elsewhere on the power board i.e. 2N5415 and 2N3440 ?
thanks
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 06, 2018, 05:31:41 PM
HH amplifiers series 100 as driver transistors use TIP29/30C.
Overheating the transistor driver can occurs if the replaced driver transistor has a larger hfe than the original driver transistor.

Each replacement driver or output transistor implies the setting of a quiet current (output) transistor.
Adjusting the quiet current is done with a fine change of the resistor R15 (AOT) which is connected in parallel with the resistor R14 (100 Ohm)
The large quiet current of the output transistors makes a great quiet current of the TIP29/30C transistor, which can be one of the reasons for heating TIP29/30C.
Driver transistor TIP29/30C and output transistor 2N3773  should be mutually matched within 10%.

TIP29/30C Datasheet
http://html.alldatasheet.com/html-pdf/2777/MOSPEC/TIP29C/145/1/TIP29C.html (http://html.alldatasheet.com/html-pdf/2777/MOSPEC/TIP29C/145/1/TIP29C.html)
http://html.alldatasheet.com/html-pdf/2781/MOSPEC/TIP30C/145/1/TIP30C.html (http://html.alldatasheet.com/html-pdf/2781/MOSPEC/TIP30C/145/1/TIP30C.html)

TIP29/30C Replacement
https://www.el-component.com/bipolar-transistors/TIP29C (https://www.el-component.com/bipolar-transistors/TIP29C)
https://www.el-component.com/bipolar-transistors/TIP30C (https://www.el-component.com/bipolar-transistors/TIP30C)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 07, 2018, 08:57:52 AM
Quote from: bobster on October 06, 2018, 02:53:22 PM
thanks G1 ,  will be a few days till i get around to it [ kids waiting on parts etc ] but will get back with some results...

can i take it that when you advise replacing the two driver transistors you mean the Tip29 and 30 [ bd711    / 712 ] ?   or are you referring to the other two transistors elsewhere on the power board i.e. 2N5415 and 2N3440 ?
thanks
rob

Hi Rob, yes it gets confusing.  :loco
I think you will find that *g1* means the PRE driver devices TIP29 & TIP30.
(I'm using the IC100 schem part names as I/We don't have your PCB in front of us)
I agree with g1 yes if those parts have smoked then likely damage to that and other transistors, I'd just replace them. ;)

TIP29/30 are the PRE drive and your large Power transistors are on a heat sink.
(is that Correct?)
Q2 is voltage gain (VAS) and then those pre and power transistors deliver the Current needed to drive the speaker.
Those last 4 transistors do the same job as a transformer in a valve amp, converting a voltage into a current.

Just like a Valve amp the output devices need to be biased.
which is what *vintagekiki* is talking about.

You likely already know that If the bias is set too hot output tubes will over dissipate and red plate.
Valves are forgiving and take a while to blow but power transistors reach a point of total destruction much faster, often instantly!! :o
Which is why you need a light bulb limiter or variac to start up a new set of transistors on a power amp.
Rail fuses are useless if something major is wrong. 8|

R34 & R28 (0R33) are a bit like the cathode resistors in a cathode biased Valve power stage. You measure the voltage drop across those and adjust the idle current of the power stage. (BTW,, 0R33 is .33 Ohms, not 33 Ohms)
Unlike Valves (which can have either fixed bias or cathode bias) transistors need that tiny resistor even though they are effectively a fixed bias.

vintagekiki uses the term "quite current" which is the same as "quiescent current". either words,, it's the idle current. :tu:

I just recently fixed a SS marshall amp that was almost identical in design with very similar issues and i just replaced the transistors and a couple of resistors,, it's faster than trying to find out what is wrong. ;)

THe reason I mentioned that speaker ground lift point is because you said this in reply 2:

"fwiw the amp all works and gives very healthy and clear output...."

So Yes,, if the speaker neg terminal is accidentally grounded in these current FB systems the power stage will run a lot hotter and IF you then load it down even more with a 4 Ohm speaker then it could do damage.
Why do I know this you ask?
Because it happened to me. :-X
the moment I removed the offending ground link the amp stabilized and worked fine.
So that is something I would be checking. 8|

Better minds here will likely know how to work out the bias voltage drop across R34 & R28 to set the correct bias.
Meantime you may want to build a simple current limiter to test it all when you get the parts.
Light bulb limiter
2nd post on this page;
https://www.ssguitar.com/index.php?board=2.0
Hope it helps.
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 07, 2018, 10:26:03 AM
gentlemen , thanks again for your informative replies , things are gradually starting to make sense to me [lol].

i'll check the speaker grounds on the jacks . I had given them all a clean but the amp was very dirty on arrival so some closer inspection is merited.....

Hopefully i'll come back with some results soon and in meantime will think about treating the old beast to new pair of driver transistors / mains caps and some attention to the biasing resistors once i do some more reading / get more confident on what i'm actually trying to achieve.

One weird thing i noticed when measuring around for DC volts was that on the output transistors 2n3773 they both had a wire coming from output board grounded to chassis on one of two nuts and bolts which secured them to chassis. ONE of these nuts read 47v but i couldn't get a reading on the other side........i followed the wire at the non-reading nut back to the circuit board and got 47v there though. [ the nut is making good contact and clean ]   
I wondered then if one output transistor is not working? But with my limited SS knowledge i would have thought that the amp would not produce any sound if one of the outputs was broken ?

For all i know if one of the outputs was goosed then 'maybe' that would cause the overheating symptoms due to other parts of the circuit trying to do all the work?        Pure speculation on my part at this stage....

cheers for now !
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 07, 2018, 02:21:12 PM
Danger!  It is imperative that you understand how the output devices are insulated from chassis/heatsink.  They need insulators (usually mica) between their bodies and the heatsink, as well as insulating spacers on the screw/nuts.  Make sure the casings of the output transistors do NOT measure low resistance (short) to the heatsink.


Sorry about the terminology with regard to the drivers.  There are a couple different ways of talking about them.  The way I was taught, we called the final transistors "outputs" and the ones before them "drivers" (in this case the TIP29C/30C).
Phil will have been from the alternate school of thought where "drivers" are the output devices (as they are driving the speaker).
So I was talking about the TIPs (in your case BD711/712) when I mentioned 'drivers' in a previous post.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 07, 2018, 04:26:23 PM
Reminder

- If you use an oscilloscope during service, be aware that the speaker is not directly connected to the ground, already is connected via the resistor R32 (0R1).

- The DC offset voltage allowed on the speaker jack is max 50-100mV

- When the power amp is defective, a DC voltage of up to 40V can occur on the speaker jack.
During repairs to protect from further damage connect speaker jack with speaker or dummy load via capacitor 2200 - 4700 uF/ 63V

- A simple current limiter to safe amp repairs can be done if instead fuse 4A in +/- 47V supply puts the resistors 100 ohm/50W

- Easy setup of the correct bias by adjusting the idle current.
a. Measurement the idle current when instead fuse 4A at point + 47V connect the DC milliampmeter (range 200mA). The idle current adjusts to value of 25-40mA by changing the resistor R15 (AOT)
b. Measurement the idle current when instead fuse 4A at point + 47V connect resistor 1R/2W and parallel with resistor connect DC millivoltmeter (range 200mV). The idle current adjusts to value of 25-40mV by changing the resistor R15 (AOT)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 07, 2018, 04:56:54 PM
thanks Kiki , i'll look into that.
The Aot resistor you mention sounds to me a bit like the resistor in valve amps e.g. Marshall that leads to the bias pot and can be changed to give more or less neg volts at pin 5 of power tubes . All new info to me and interesting stuff..
cheers for now guys
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 08, 2018, 08:44:01 AM
Hey Bob, Any chance you could post a few pictures of the circuit board so we can get a better idea of how this thing is wired up? That would speed up the process. :dbtu:
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 08, 2018, 12:02:11 PM
Hi , some phone pics here hopefully they will upload ok.....
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 08, 2018, 01:28:21 PM
I hope you saw my last post about how the output transistors and the wires to them must be insulated from the heatsink/chassis.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 08, 2018, 03:33:58 PM
Yes G1 i did ,  i made sure the little mica spacers are in correct position next to chassis
cheers Rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 08, 2018, 05:33:29 PM
P.S. i have just noticed on my pics of the power amp circuit board that R15 [ the AOT one Kiki referred to ] is missing....it looks as if there has never been any resistor in these slots as there is no evidence of previous solder-

it is also missing on the board of my HH VS musician amp which works without any issues....

As far as i can make out it is [ or would be if present ] in parallel with a 100ohm resistor  'R35'.....

Maybe it was not required in these two amps and the R15 slots are there as an option for amps that are harder to bias?

It seems odd that it is missing though and i wonder if putting a resistor in that slot would help cool things down ?
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 09, 2018, 04:10:35 AM
Quote from: bobster on October 08, 2018, 05:33:29 PM
Maybe it was not required in these two amps and the R15 slots are there as an option for amps that are harder to bias?

It seems odd that it is missing though and i wonder if putting a resistor in that slot would help cool things down ?

Makes no sense to try that as the amp worked fine for many years. 8|
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 09, 2018, 04:16:14 AM


From First post;
Quote from: bobster on September 26, 2018, 11:46:06 AM
recently purchased HH IC100 amp circa 74 -75.
Amp has been working fine for long periods and is out of the shell just now for a clean and visual inspection.

OK so Amp worked fine.

Then you say;
Quote from: bobster on September 26, 2018, 11:46:06 AM
Earlier on i tried a treble booster through the amp at low volume and saw smoke from the power board and amp stopped working.

Was this before or after you cleaned it?

My point being if the amp worked fine and then you pulled the lid to clean it you may have unknowingly made a mistake which caused the problem.

It only takes a hair thin strand of loose wire that gets dislodged in a clean to cause problems.

Can you take an internal pic of the two speaker output sockets?
They MUST be Insulated from Chassis otherwise it will kill the amp.
Phil.

Title: Mounting a transistor to heatsink
Post by: vintagekiki on October 09, 2018, 09:00:13 AM
- When replacing the output transistors, it is  necessary to clean the heatsink and insulating washer from the old thermally conductive paste with a some solvent on a nitro base.
- In order to better cool the transistors, apply to the insulating washer fresh thermally conductive paste on both sides.

https://rimstar.org/equip/mount_transistor_heatsink.htm (https://rimstar.org/equip/mount_transistor_heatsink.htm)
Mounting a transistor to heatsink

https://www.youtube.com/watch?v=hNRacVQRgBc
How to mount/attach transistor to heatsink
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 09, 2018, 09:34:24 AM
hi Phil , i had cleaned the amp just by spraying contact cleaner to the pots and switches, isoprop alcohol to jack contacts and a general de-greasing of dirt on cosmetic surfaces / facia....

When i said it was working ok for long periods , this was after i had cleaned it and that referred to when i had it idling at low volume in the house into a 16 ohm cab but i wasn't playing much or loudly....

It was a couple of days later when i tried the treble booster [ into an 8 ohm cab at that time ] and that is when i noticed the smoke coming from the resistors [ replaced as discussed ] on the power board and the heatsink of the BD711 being hot.....

i will post some pics of the speaker jacks for review...thanks Rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 09, 2018, 03:50:45 PM
Hi gents
finally got a chance to do some DCV readings with no load.......some of them seem weird but hopefully they will make sense to those of you with the know how....

TIP29c [ BD711 on my amp ]    C = 46.5v  B = 1v      E = 0.5v
TIP30c [ BD712 on my amp ]    C =    - 46.1v  B = - 0.6v   E = 0v

DC mv across  R28    = 5.1mv
DC mv across  R34    = 4.9mv

Power Q's
Q1    2N3773      C = 46.5v    B = 0.5v     E = 0v
Q2    2N3773      C = 0v         B =  - 46.8v   E =   - 46.8v

thanks
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 09, 2018, 05:24:07 PM
Quote from: bobster on October 09, 2018, 03:50:45 PM
DC mv across  R28    = 5.1mv
DC mv across  R34    = 4.9mv

In your case if R28 = R34 = 0.33 Ω idle current through 2N3773 is
DC mv across  R28    = 5.1mv = 0.0155 mA
DC mv across  R34    = 4.9mv = 0.0148 mA
2N3773 are at beginning opening
For optimal bias idle current it should be increased to 25-40mA
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 09, 2018, 06:32:05 PM
hi Kiki , thanks for reply
it's easily possible i have read them wrong somehow as that seems very low doesn't it..

it's late here and will need to get kids to bed but will double check the reading tomorrow.
The amp sounds clear and loud fwiw lol
cheers
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 10, 2018, 07:55:52 AM
hi , tried the amp again today through 16 ohm. got 15 minutes then r29 [ 33 ohm ] started burning . According to schematic this is associated with the emitter of TIP29c [ BD711 ]  that is overheating. This TIP29c emitter also looks like it's tied to the base and emitter [ emitter going through R29 of 33ohm first ] of the 2N3773 ..

I don't know enough about these amps to tell what is causing excess current draw ? i'm wondering if either the TIP29c is faulty , or is one of the main output 2N3773 transistors out of commission and leaving the other one overworked?

I can't make sense of the voltage readings above that i took yesterday so if anyone can decipher anything from them i'd be glad to hear ..
thanks rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 10, 2018, 08:28:08 AM
Hi Bob,
OK so it's slowly overheating while running with what sounds like a good clean strong signal.
I would be more concerned about Q2 as I think you mentioned R10 was replaced as it was burnt.
If Q2 has an issue then of course the next transistor is going to fail/ overheat

You might have HF runaway if R10 burnt then C5 would have copped a flogging and might be dead.
That 150pF cap is for hiFreq compensation (IIRC)
if it's now open circuit then the amp might be driving some RF that only bats can hear at 100 plus watts, and would certainly overheat the output.

Phil.

Yea thanks for the photos of output sockets,, they look fine. :tu:
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 10, 2018, 10:15:52 AM
Hi Phil ,
the resistor R10 has been fine since replacement and only looked a little burnt so i changed it out early on in this process . The one that is burning up when i play is R29 [ 33ohms ] .
Easy job to replace the 150pf cap though so will do that....

Have now replaced main filter caps 4700uf x2 but this has not made a difference to weird voltages.

I have an old HH PA amp power circuit board which i have relieved of its driver transistors
they are 2x  'D381' and 2x 'B536' which seem to be close in spec to TIP29c and Tip30c .

On my multimeter transistor hfe test setting the D381s read 53 and 15 [15 seems low? ]
the B536's read 141 and 134.

I'm up for trying these as replacements in the IC100 but would appreciate advice as to which pair will be best hfe wise ?   I'm assuming the 53 and 141...

Also , I am not sure of my previously mentioned dcv readings on the 2N3773 output transistors and whether replacing the drivers will make no difference if there is a fault with one of the 2N3773's ?
thanks
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 10, 2018, 12:02:10 PM
ok something interesting is happening ......
replaced c5   with a ceramic 150pf 

Now 'Q2' [ pre driver?]  2N5415 is heating up real fast and the previously heating BD711 driver is remaining cool...

Also , the sound output is now distorted and unpleasant like crossover distortion you would hear on a valve amp , still fairly loud though.........I wonder if this is because i'm only getting 0.5mv dc over the OR33 resistors and Kiki pointed out this would be an issue.....

For comparison I checked my HH VS musician amps readings and get around 11mv on it's OR33's

took some voltages on the first two pre driver transistors on the IC100-

Q1      2N3440      C = 46.9v      B = 0.6v      E = 0.1v
Q2      2N5415      C = 1.2v        B = 46.9v    E = 47.4v

also took voltage readings on my HH Vs musician head in relation to pre drivers / drivers and power transistors and get largely similar results to what i read on the IC100 amp we are looking at...

so something appears up with the biasing maybe?

any ideas ? ;)
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 10, 2018, 09:53:12 PM
Where is your (-) supply rail, or are you just omitting the minus sign from your voltage readings?
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 10, 2018, 10:02:07 PM
Quote from: bobster on October 10, 2018, 12:02:10 PM
For comparison I checked my HH VS musician amps readings and get around 11mv on it's OR33's

11mv on it's OR33's on your HH VS musician amps is 33 mA idle current and that's OK.
When replacing the transistor, check that the CBE transistor layout is the same.

Question.
Is there and how much is DC offset on speaker output jacks?

How much is the current, and how much is the DC voltage without signal at + and - supply rail (measured at Fuse 4A)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 11, 2018, 06:12:34 AM
good question G1 , i freely admit to being a little out of my depth here and was omitting the - sign from the results as you pointed out .

Kiki , there is 4mv on the speaker out jacks.....

measuring over the 4A resistors i get around 0.5mv....very low i suspect

i'm not sure how to measure current though , sorry....
i have a decent fluke meter but not sure how to do the current test

thanks again guys for your patience...

next up i'm going to check the little BC204 and BC207 transistors to see what they read...

as per schematic
Q3  BC207    C = 1v   B = 0v   E = 0v
Q4  BC204    C = 0.4v   B = 0v  E = 0v

cheers for now - rob

Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 11, 2018, 08:47:57 AM
I just whiped up a quick sim of the power amp circuit for you.
Will give some idea of voltages around the circuit.
Don't rely on this as gospel cause the devices are perfect models and real world devices will be different but gives a fair estimate of what is happening.

Not shown here but this sim shows that R34 and 28 are sitting around 40mW with a 100mV input outputting about 2 Watts into 8 Ohm load.

Regarding the bias; Yes you maybe right,,check that R35 and D3 are in fact working as that would upset the outcome.

Q 3&4 and all associated parts are the current limiting section and only turn on when the output is shorted or reaches the set limit, otherwise they are out of circuit.
I've left them and other bits out for clarity.
Sorry that C5 was not the issue and set you on a bum steer. :-[

Keep an eye out for solder cracks, at the age cracked solder pads can be an issue.

Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 11, 2018, 09:34:11 AM
hi Phil , thanks so much for taking the time to do that it's much appreciated .
Going to get little 'un from school and will have a look later at this and also the R35 and diode .....

cheers!
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 11, 2018, 10:19:51 PM
Be sure to note the (-) sign on any readings when it appears.  We are expecting it for about half the amp and will think there is a fault if you omit it where it should be noted.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 11, 2018, 10:50:57 PM
Quote from: bobster on October 11, 2018, 06:12:34 AM... there is 4mv on the speaker out jacks ...

The DC offset voltage is OK (allowed max 50-100mV)

Quote from: bobster on October 11, 2018, 06:12:34 AM... measuring over the 4A resistors i get around 4.5mv ...

idle current power amp with high accuracy can be measured by measuring the idle current 2N3773 described at
https://www.ssguitar.com/index.php?topic=4500.msg36012#msg36012

a. recommended value measurement with DC milliampmeter 25-40mA
or
b. recommended value measurement with DC millivoltmeter 25-40mV
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 12, 2018, 10:06:38 AM
Hi guys , thanks again for your patience...i feel like i'm learning something here lol.

here are some revised [ amp unloaded ] readings including negative voltage results-

741 opamp on power board

pin 1  =  - 15.2v         pin 8   = 0v
pin 2  =   0v               pin 7   =  + 14.8v
pin 3  =   0v               pin 6   =  + 0.7v
pin 4   =  - 15.2v        pin 5   =   - 15.2v

TIP29c [ BD711 on my amp ]    C = 46.5v  B = 1v      E = 0.5v
TIP30c [ BD712 on my amp ]    C =    - 46.1v  B = - 0.6v   E = 0v

DC mv across  R28    = +0.6mv     [ on 200mv scale , i had previously mistaken these as ~6mv ]
DC mv across  R34    =  +0.6mv

Power Q's
Q1    2N3773      C = 46.5v    B = 0.5v     E = 0v
Q2    2N3773      C = 0v         B =  - 46.8v   E =   - 46.8v


2N3440     C = 46.9v   B = 0.6v   E = 0.1v            [ all positive voltage readings ]
2N5415     C = 1.2v     B = 46.8v     E = 47.4v      [ all pos voltage readings ]

*2N5145 is now heating up fast and the Tip29c is no longer heating up since i replaced C5 of 150pf as suggested in case of high freq osc....

R10 of 100 ohms has +47 volts at either end of it
C5  of 150pf [ replaced ]  has +47 at one end and + 1.2v at the other end which is collector of 2N5415 i think

the junction between R35 of 100 ohms and D3   has + 109mv which then after a short time drifted down to around +100mv

According to the power amp sim Phil put up this reading between R35 and D3 should be negative and around -155mv?

hope all this gives a clue as to what parts may need replaced

p.s. amplifier is still working but sound remains distorted at any volume
thanks  rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: solderer25 on October 12, 2018, 10:21:49 AM
From your readings I would suspect Q2 is faulty as there should be about 0.6V DC difference between the B and E terminals. To me it looks like internal dead short between base and emitter. I would replace Q2 anyway on that evidence.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 12, 2018, 10:54:56 AM
thanks for this , solderer

Just to confirm , when you say Q2 , does that mean the 2N5415 or is it one of the power pair 2N3773?

And would still be interested to hear from Phil and the others if there is anything else amiss with these readings as i'd hate to replace this transistor or another part for it just to pop again a minute later ;)

i have added the 741 opamps readings to the post 2 or 3 above for reference also



cheers
Rob 
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: solderer25 on October 12, 2018, 02:49:29 PM
I am talking about the lower of the two 2N3773 output transistors. If it was myself working on the amp I would first remove all the connections from this tranny and do a resistance check across the B/E terminals. If it reads zero on resistance range that is your problem (or one of them!) and the device must be replaced. Hope this helps anyway.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 12, 2018, 03:26:52 PM
thanks , will look into that and deconnect  /  test them soon......family stuff getting busy .. :duh

cheers rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 13, 2018, 05:07:41 AM
Quote from: bobster on October 12, 2018, 10:06:38 AM
p.s. amplifier is still working but sound remains distorted at any volume
Turn guitar to poweramp input jack (rear amp).
In this way, you separate the preamplifier from the power amp.
The sound from the amplifier will be much smaller.

- If the sound is further distorted, fault is in the power amp.
- If the sound is clean (non-distorted) fault is in the preamplifier.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 13, 2018, 08:45:13 AM
Quote from: solderer25 on October 12, 2018, 02:49:29 PM
I am talking about the lower of the two 2N3773 output transistors. If it was myself working on the amp I would first remove all the connections from this tranny and do a resistance check across the B/E terminals. If it reads zero on resistance range that is your problem (or one of them!) and the device must be replaced. Hope this helps anyway.

If that is dead, I'd be replacing all the transistors, as R10  around Q2 (the VAS one)was overheating so likely others are stressed by now. The 741 is likely fine.  IME not worth fiddling around.
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 14, 2018, 10:58:02 AM
hi Kiki and Phil
tried the guitar through 'power amp in' and it remains very distorted so looks like power amp right enough.

I have replacements here for the tip29 and tip30 robbed from a dead HH pa amp and that read Hfe of 53 and 130 on my meter.

So would the plan be -
Order up a new 2N5415 , test the 2N3773's as described above and if no reading from B to E replace and see if we get a result ?

Anything els you could advise that needs done ?
Would be interested in your assessment of my updated voltage readings in post number #39 above....

Will be a few days till i get round to this as have a newborn in here plus the other monsters but will get back to all soon.
thanks again for all the help so far

cheers
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: sj-castle on October 14, 2018, 02:02:53 PM
Hi all thanks for all this great information and to every one contributing here. I also have almost the same exact problem.
The amp was not in heavy use but was working fine until last week when turned on it was fuzzing away and the back plate heating up hot. I have replace the 4700 caps as one of the originals had blow a hole in its top. The amp now is (working) you get a clean sound but still heating up, but not all the time so a bit tricky to pinpoint whats gone.

Out of interest in my version R15 is also missing AND C4 also never installed, no solder on pads.
Using my DVM on diode test the two driver Trs look good showing a diode drop to base from collector and emitter. But the upper TIP29 is running hot, the main concern is the heating of the back panel. ie the 2N3773 should I just replace them.

I was in the process of measuring +/- rails etc, when it started getting hot again and the + had dropped to 40 at that point.
I will continue testing. I have access to a scope if need be but would not know what to check with it.

Thanks again to all.
... Simon
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 14, 2018, 06:26:19 PM
Do not replace ad hoc any transistors, if not previously tested them in what condition.
Test each transistor with the multimeter in the circuit or removed from the circuit.

Testing a transistor with an analogue multimeter
https://www.radio-electronics.com/info/t_and_m/analogue-multimeter-voa-vom/testing-diode-transistor-with-multimeter.php (https://www.radio-electronics.com/info/t_and_m/analogue-multimeter-voa-vom/testing-diode-transistor-with-multimeter.php)
https://www.instructables.com/id/How-to-test-Bipolar-Transistors-if-you-have-an-Ana/ (https://www.instructables.com/id/How-to-test-Bipolar-Transistors-if-you-have-an-Ana/)
https://www.scribd.com/doc/34162981/Transistor-Test-Using-an-Analogue-Multi-Meter  (https://www.scribd.com/doc/34162981/Transistor-Test-Using-an-Analogue-Multi-Meter)
https://www.mikroe.com/ebooks/components-of-electronic-devices/diodes-and-transistors  (https://www.mikroe.com/ebooks/components-of-electronic-devices/diodes-and-transistors)
http://120studio.com/tech/transistors.htm  (http://120studio.com/tech/transistors.htm)

Simple transistor testers
https://www.elprocus.com/simple-transistor-tester-circuit/ (https://www.elprocus.com/simple-transistor-tester-circuit/)
http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/images/TransistorTester.gif (http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/images/TransistorTester.gif)
https://electronicsforu.com/electronics-projects/hardware-diy/easy-transistor-tester  (https://electronicsforu.com/electronics-projects/hardware-diy/easy-transistor-tester)

From the 30 year practice, the most common failures in power amp are the output transistors 2N3773, the driver transistors TIP29C/30C, the emitters resistance 0.33Ω/6W.
After each power amp repair, necessarily set the idle current 2N3773, and check the DC offset on speaker output jacks.

Reminder for advanced users
If you have tone generator, oscilloscope, audio voltmeter and 8 Ω dummy load, by measuring voltage at audio voltmeter, check at the oscilloscope at which power, power amp is symmetrically limited.
P = U2 / R
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 15, 2018, 07:18:43 PM
thanks Kiki ,
i've desoldered the power and driver transistors from a donor pa head and will test them all using the info from your links to see which ones may be feasible to use....

i'll also take readings from my VS musician head which is working fine and compare them to the corresponding parts in the IC100 i'm trying to repair and see if anything else looks weird.

I'm enjoying trying to learn here but it's certainly quite complex compared to my dinosaur valve rigs ;)
cheers
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 16, 2018, 03:09:00 AM
I'm not old-fashioned, but the ohmmeter in the analog multimeter 20 kohm/V (with pointers) best proved for a semiconductor test in the circuit.
Measurement with ohmmeter (measurement range x10 or x100) can detect a faulty semiconductor in a circuit without desoldering.
If you have a 2 amplifier with the same part number PCB (for example AS 00014/2), simply compare the same semiconductor in the same conditions in the correct and in the faulty amplifier.

Warning.
Disconnect amplifier from the AC outlet.

When any measuring with ohmmetar, amplifier must be disconnect from the AC outlet.
When desolder any component, the amplifier must be disconnect from the AC outlet.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 16, 2018, 01:28:26 PM
ok Kiki , appreciate the safety warning...

i have a fluke meter only so hopefully it will help make sense of things when i get round to these tests soon...

cheers
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 19, 2018, 01:18:53 PM
hi guys
just on to ask for some more advice before i attempt any more of this repair with the IC100.....

i have taken readings off the driver and power transistors in circuit in the IC100 and my working VS-Musician head with power on ..

all transistors read similar except for the lower of the 2N3773's which reads - 47.2v on its emitter while the 2N3773 in the working VS Musician amp reads 0v...

I tried another two 2N3773's from a scrap donor PA amp but got the same results with distorted output so they were both likely to be dead....

At this stage the 2N5415 is still overheating but the previously overheating tip29c is now not getting overly warm but they give very similar DCV results to the working VS amp so might still be serviceable

in your experience , does this look like i just need a new 2N3773 [ or pair of ] ?
thanks rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 20, 2018, 09:34:47 AM
Although both may use the same transistors they could be completely different designs.

Q/ Do both amps use split supply rails?
If the VS head reads 0Volts on the emitter it maybe single supply in which case it would read 0Volts.
Just look for your main filter caps,, does the other VS head only have one big electro cap?
if so it's a single supply circuit.
Chum,,,
You are chasing your tail using second hand parts,, Just go buy some NEW parts,,, build a light bulb limiter  :trouble
(so you don't burn out new parts before you have a chance to check for faults),,
with no speaker,,fire up the amp and check voltages.
If the output is close to zero VDC then read the voltage drop across R28 & R34 do some maths and if all is well then  connect the speaker.
*ALL that is done with limiter in circuit*
When you are confident that the circuit is stable then you remove the limiter and recheck voltages.

Of course with limiter in place voltages will be lower so you have to recheck the voltages and the bias.

I recall you replaced C5 and it distorted badly,, I hope you removed it and reinserted the old one?
The original looks like it could be a mica cap ,, I'm not sure but maybe ceramic won't work there.
Also the ceramic may be a low voltage type and hence it has failed.
Others here may know a more professional way to fix this but that is how I do it.
I run power amp repairs full bore into a load with lamp limiter on and read the voltages while it's working to weed out any lurking problems. ONLY then do I remove the limiter.

As I'm not a teck by trade I don't try to fix exotic circuits that are way beyond my ability to fix.
As I tend to get a fair amount of 60's 80's Amps they are often small fairly simple circuits and hence easy to fix.
I did pm you about this a week back but maybe you have not checked your messages.
Phil.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 20, 2018, 11:48:50 AM
Hi Phil , thanks again for your help.
I never got an alert for a PM but will check the messages here...
i have also ordered two new 2N3773's and a 2N5415.....

the other amp i made the comparisons with is from the same stable and maker and it's power board is very similar in design and interchangeable as far as i am aware and also has the same two big electro caps and general topology   .
i did suspect that little 150p cap [ threw the old one out unfortunately ] and will have a look in my stash for a non ceramic replacement and try it there to see if anything gives..
i only tried the scrap amps 2N3773's as an experiment as i have to wait for parts to arrive but did think they would be likely to be dead ..
i am reading very low mv on speaker outs well within limits according to Kiki...

happy to admit i'm floundering here but am determined to get this amp working again and am not in a major hurry plus i'm learning [a little! ] along the way ;)
thanks
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 20, 2018, 01:50:45 PM
The VS musician can not work if it has 0V at the lower 3773 emitter.
So you may be mixing up the lower and upper 3773's, or mixing up emitter and collector.
The 'lower' will have -48V on one of it's terminals.

How about posting your E,B, & C idle DC voltages for the 2N5415, Tip29, Tip30, upper 3773, lower 3773.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 20, 2018, 08:55:00 PM
hi G1 ,
i took these voltage readings a few days ago and have copied from another post earlier in thread...

TIP29c [ BD711 on my amp ]    C = 46.5v  B = 1v      E = 0.5v
TIP30c [ BD712 on my amp ]    C =    - 46.1v  B = - 0.6v   E = 0v

DC mv across  R28    = +0.6mv     [ on 200mv scale ]
DC mv across  R34    =  +0.6mv

Power Q's
Q1    2N3773      C = 46.5v    B = 0.5v     E = 0v
Q2    2N3773      C = 0v         B =  - 46.8v   E =   - 46.8v


2N3440     C = 46.9v   B = 0.6v   E = 0.1v            [ all positive voltage readings ]
2N5415     C = 1.2v     B = 46.8v     E = 47.4v      [ all pos voltage readings ]

*2N5145 is now heating up fast and the Tip29c is no longer heating up since i replaced C5 of 150pf as suggested in case of high freq osc.... [ it's possible my replacement C5 is faulty so will will try another one there soon ]

R10 of 100 ohms has +47 volts at either end of it
C5  of 150pf [ replaced ]  has +47 at one end and + 1.2v at the other end which is collector of 2N5415 i think

the junction between R35 of 100 ohms and D3   has + 109mv which then after a short time drifted down to around +100mv

According to the power amp sim Phil put up this reading between R35 and D3 should be negative and around -155mv?

hope all this gives a clue as to what parts may need replaced or are causing issues...

thanks rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 21, 2018, 11:54:18 PM
The 2N5415 is a metal can with a heatsink?  Don't be alarmed, they are expecting it to heat up, that's why there is a heatsink on it.
Most of your voltages seem in the ballpark.  The ones in the bias string (R35/D3) will be off a little until the resistor adjustment at AOT resistor is made.  That adjustment will also get the voltage across R28 and R34 into the range that vintagekiki showed, a couple millivolts each should even do the trick.

I think there is one typo in your measurements, but double check it.  You said Tip30 collector was -46.1V, and it is directly connected to lower 2n3773 base.  You reported -46.8V there, I think it should read -46.1V like at the Tip30.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 22, 2018, 04:29:26 AM
hi G1 ,
yes possibly a typo there as i measured these voltages at different times before and after changing the main filter caps.....
Also , there is no AOT resistor on the power board R15 position ,the solder holes are empty in this amp and the other two HH chassis' i have here so i'm not sure how else i can set the bias which at the moment is extremely low across the 0.33ohm resistors as in 0.5mv instead of around 11v in the working amp ..

the 2N5415 does have a heatsink as you say and shows similar voltage results to its corresponding transistor on my other HH amp [ the working VS musician head ] .

The one voltage reading that stands out as odd to me in the faulty amp is the lower 2n3773 emitter which is reading approx - 47v on the faulty amp but reads 0v on the working one.
I may have mixed up the emitter and base readings but i don't think so as the wires are colour coded and connected to the same terminals on each power board which are apparently interchangeable.

Either way , on the working VS amp i am only reading approx - 47v on ONE terminal of the 2N3773 but on the faulty amp i am reading approx - 47 v on two of the 2N3773 terminals.....

I noticed the distortion started shortly after i replaced the two main filters from a donor spare chassis which hadn't been used in awhile but the caps showed no sings of venting whereas the ones on the amp had started to let go of some dried up innards.........so it's possible these caps are skewing something...

Also i need to change out the little C5 cap again to see if it helps as the distortion appeared shortly after i changed this cap and the filters so one or both may be a factor.....

These two changes are the only ones that i've done that i can think may be clouding the issue separate to the original problem of overheating in the Tip29c which is no longer happening lol...

I'll change these parts out soon and report any changes but am still mystified as to why the 2N3773 is showing two readings of approx  - 47 v when on my other working amp its corresponding transistor is only showing one..

thanks
rob
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 22, 2018, 11:04:28 AM
well guys , seem to have some progress now....

as i was suspicious of the reading from the lower 2N3773's emitter....i followed the trace on the board from it and found R33 a little 33r which corresponds to the R29 33r for the other 2N3773 which i thought had previously burned and had replaced.....

When i saw smoke previously it may actually have been this resistor [ r33 ] that was burning as it is not far under R29.
Its partner R29 was the only one that i thought was 'under pressure' at the time .
So today i popped in two new 33r 1 watt resistors to these two positions and now have a nice clear sounding amp again.

The Tip29c is not overheating any more and i am reading 4.5mv over the large 0.33 ohm power resistors which is an improvement from 0.5mv.

Hopefully this has cracked the problem..

Will take the amp to a gig soon [ with a spare ] and put it through it's paces and if it survives that we might even be good to go

i feel i have learned a bit here on SS amps and am perhaps not so intimidated by them as i used to be lol

many thanks to G1 / Phil / Kiki and everyone for the help with this it's very much appreciated

cheers - Rob 8)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: vintagekiki on October 22, 2018, 11:57:25 AM
The collector current that flows through TIP29/30C creates a voltage drop on resistors R29 / R33 = 33 Ohm connected between the base and the emitter of the output transistors 2N3773, and in this way provides the necessary bias for their operation.

Transistors for their work should have a voltage between the base and the emitter about 0.55 - 0.7V.

At low power transistors on PCB, ebc connections are near, so you need to be careful when performing measurements directly on transistors

Tip
For future reference when the power amp repair, replace the defective output transistor(s), the emitter resistor(s) of the defective output transistor(s), the both resistors of the base/emitter of the output transistors, the drivers if the defects are changed in pairs (TIP29/30C), check and adjust the idle current (25-30 mA per pair of output transistors).
Check the DC offset (≤ 100mV) of the speaker jack connector and that's it.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 22, 2018, 03:36:13 PM
thanks Kiki , will keep all this info in my files for the future ;)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: g1 on October 22, 2018, 06:10:13 PM
Quote from: bobster on October 22, 2018, 04:29:26 AM
The one voltage reading that stands out as odd to me in the faulty amp is the lower 2n3773 emitter which is reading approx - 47v on the faulty amp but reads 0v on the working one.
I may have mixed up the emitter and base readings but i don't think so as the wires are colour coded and connected to the same terminals on each power board which are apparently interchangeable.

Either way , on the working VS amp i am only reading approx - 47v on ONE terminal of the 2N3773 but on the faulty amp i am reading approx - 47 v on two of the 2N3773 terminals.....
...
am still mystified as to why the 2N3773 is showing two readings of approx  - 47 v when on my other working amp its corresponding transistor is only showing one..
You may have to dig in the probes more to get the reading on the Musician. 
The amp that is giving readings around -47V on 2 terminals is correct.  (should be roughly .6V difference between E & B terminals). 
If the VS Musician really measures -47V at emitter and 0V at base (of lower 2n3773), there is something wrong with it.
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 22, 2018, 06:53:38 PM
Hi G1 , yes you were right when you thought i had read the terminals wrong in the VS.
It does in fact have the two terminals reading approx -47v

On the IC100 i worked on earlier i am getting the slight voltage ~ 0.6v difference that you state between the two terminals B and E....

thanks again for all the tips i've enjoyed getting a little bit of insight into the SS world
rob

Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: phatt on October 23, 2018, 08:39:41 AM
Great to hear you got it working. :dbtu: :dbtu:

If you want to learn more about SS gear a good place to start is here;
http://sound.whsites.net/index2.html

I find the site map more useful for finding a particular subject;
http://sound.whsites.net/site-map.htm

You will need a long weekend and a month of sundays to get through all the pages.  :)
Phil.
Title: Out of rehab into recovery
Post by: sj-castle on October 24, 2018, 02:37:23 PM
Out of rehab into recovery.
So the amp is working better than it ever has for us. It was gifted to my son 4 years ago but it had not seen much love in its life for quite some time before that, as it had been relegated to the garage, shed and who knows where else before we gave it a decent home.

Any how, this is what I did.
I could not measure any sensible continuity between the fuse posts so decided to replace them with some scrap I had kicking around. Not an ideal match but they work. As can be seen the corrosion was quite bad and I wonder how the thing actually work in the past months. With the fuses out I measured the no load idle current at 1.8A so something was up. I removed the cabling from the main TRs which all had ~0.4V forward drop across each junction which I guess is ok. The terminal post bolts were also replace due to corrosion while they were out.

On to replacing parts, I pulled all the electrolytics and tested them (get yourself one of the shown cheap testers if you don't have such a thing). Both the 10v 47uF caps were dead and the 6.8 didn't look too good, so I replaced them. The local electronics shop only had one 6.8. For the time being, the best of the two is back in for now (C6). I also pulled the 150pF which looked good showing 144pF on the tester so that's back in. The only real problem is that possibly due to its hard life in some cold dark damp place the tracks/pads easily lift from the PCB when soldering.

The amp is now playing very well and loud, with no heating while idle.

My question is how hot does the back panel get when playing at volume, I know this is a bit subjective with out a proper reading, but it was quite warm after being played hard on stage setting for 10 mins or so. I pulled it from the cabinet and the two TIP drivers where more than warm but not burning to the touch (not uncomfortable and no smell)
would this be acceptable ?

... Simon

Title: Re: Out of rehab into recovery
Post by: vintagekiki on October 24, 2018, 03:54:58 PM
Quote from: sj-castle on October 24, 2018, 02:37:23 PM
My question is how hot does the back panel get when playing at volume, I know this is a bit subjective with out a proper reading, but it was quite warm after being played hard on stage setting for 10 mins or so. I pulled it from the cabinet and the two TIP drivers where more than warm but not burning to the touch (not uncomfortable and no smell)
would this be acceptable ?

The best test of whether the amplifier overheats or not, is to follow the rear panel (heat sink) heating for 30 minutes without the signal (guitar is not connected).

The operating temperature of the rear panel (heat sink) without the signal should be slightly warm up to 30-40 degrees.
When the signal (guitar) is connected to the amplifier  and when playing a loud, normal operating temperature the rear panel (heat sink) is very hot to 70-80 degrees.

Tip
When examining passive components, be careful not to make a mistake in interpreting the measured nominal value and tolerance ratings.
The usual tolerance rating of most components is +/- 10-20% except aluminum electrolytic's which can range from -20% to as high as + 80%

https://www.google.com/search?q=resistor+and+capacitor+tolerance+rating (https://www.google.com/search?q=resistor+and+capacitor+tolerance+rating)
Title: Re: HH IC100 overheating BD711 transistor...help !
Post by: bobster on October 25, 2018, 10:10:50 AM
thanks Kiki , that's good to know.....

Fwiw , i often put a small desk fan behind my amps at gigs , most of the places i play are low on space and the amps can end up pushed back against a wall and have little to no ventilation.

The fan is mainly for extra insurance to keep them cool as most of my amps are 40 years old plus lol

I also use lots of boost pedals etc and this can also cause amps to draw more power and put pressure on older components so by keeping them cool like this i have rarely had any failures over the years..
cheers
rob