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Messages - phatt

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1
The Newcomer's Forum / Re: Heathkit TA16
« on: May 11, 2019, 09:48:32 AM »
Nope ya goin' the wrong way, could lead to more mistakes xP
 Establish those voltages FIRST. 8|
The pic quality is good but we need the whole board
Some good clear pics of both sides of the board will help a lot ;)
Phil.

2
The Newcomer's Forum / Re: Heathkit TA16
« on: May 10, 2019, 10:01:09 PM »
That is *Normal flux residue* and has no effect on circuit. :tu:

Re file size,
When you load attachments it tells you the file size limit;
*maximum individual size 5120KB*

If it helps,,
Download this; https://www.irfanview.com/
I've used this for years and could not work without it <3) <3)

Does just about anything you throw at it,,, and it's FREE! :dbtu: :dbtu:

Load your pic and from the drop down menu called *Image* click *Resize/Resample* (or hit Control R)
Now click on *Half size*,, hit OK.
 Then  *Save AS* select *File Type* as a *JPEG*

That will reduce a 7Meg file down to  maybe 500kb.
Don't forget to rename the file if you want to keep the original. 8|
HTH, Phil.

3
The Newcomer's Forum / Re: Heathkit TA16
« on: May 08, 2019, 07:34:10 AM »
Hi Glen,
         Yes hard to know where to start but *JazzBass* means disconnect the speaker,,  the Amp drives a load which is the speaker. Load is tek talk for the speaker. ;)
Assuming you have a meter,, set it to the highest DC voltage.

With speaker disconnected probe the output speaker terminals/wires and it should be very close to Zero VDC less than 0.5VDC.
Now with Ground probe on chassis the first DC supply is found at the output of the Bridge rectifier. (Marked G)  The rectifier is those 4 diodes marked D102 to D105.

(J) is common or ground and often also connected to Chassis but not always.

The voltages are on the schematic,, if not sure where they are on the circuit then often the Electrolytic caps will give you a clue as to where to find those voltage nodes.
they will not read Exactly the same but as long as they read close it's all good.

Some old amp layouts are quite dangerous so be aware of the mains input wires it can KILL you.  8|
 I Cover any bare terminals that hold mains voltages when I have to work on that stuff.
Phil.

4
Schematics and Layouts / Re: Dual or Split supply Audio amps
« on: May 07, 2019, 05:11:13 AM »
Be aware as there are caveats on the full power option.  xP
The novice might miss the limitations of using 30-0-30VDC supply rails.
You will likely blow the chip if you use a 4 Ohm speaker. (it's written in the specs)

This is a small chip with small surface area and the laws of fizzy stuff tells you it cannot dissipate the heat required to run 4 Ohms at high rail voltages.
so 25 Volt rails is a good safe option. 8|
If you want more grunt then you need a bigger Amp that can dissipate the heat.
Phil.

5
Preamps and Effects / Re: implementing presets
« on: May 02, 2019, 02:51:03 AM »
Hi Jon,, welcome :)
Not a simple project xP  You will need relays, dedicated foot control switches and a one off circuit which may require more power than the tiny 10 watt amp can deliver.
So in my observation it's *False economy* a whole lot of work for little return. :'(
When you can buy a nux pedal (or similar) with 100 user settings for under $100Au
then it's a no brainer. 8|
I'm aware that a lot of players like the idea of an *All in one* amp that does it all but it's rare to find and ones that are capable are likely to cost a small fortune. :-X

As much as I hate the idea of pedal boards they are extremely useful and cost effective.
Also allows for swap and go changes to get other capabilities. Dedicated *Do it all* Amps are not swap and go friendly.
Phil.

6
Schematics and Layouts / Re: Dual or Split supply Audio amps
« on: April 30, 2019, 07:23:02 AM »
A couple of Q's first,, What size & power speaker are you using?
If you are only using small speakers you won't get full power.

What is the rating of the power transformer? That is another limiting factor.
maybe post some pics of you builds :tu:
Phil.

7
Amplifier Discussion / Re: Unicord Stage 65b Output Transistors
« on: April 29, 2019, 03:44:36 AM »
Hello. I have been working on a Unicord "Stage" 65b amplifier and ordered and installed replacement output transistors Sanyo B507E and D313E. They work alright with a signal from a generator or guitar at very low volume but  heat up and will burn/short out completely if left on with a louder volume setting. The sound is good out of an 8 ohm speaker until it is turned up, then they heat up. They would be normally mounted to the chassis to dissipate heat but they are burning hot anyway. The speaker reads ok at 8 ohms. I am suspecting the Chinese transistors I bought from e-bay are cheap junk and that is the problem. Any experience or advice on this? Should I buy an equivalent?
Tx

ARRRRH,,  :o  Stop!!!  :o They have to be mounted BEFORE you turn on anything.
That is why the heat sink is there,, they cannot work without a heat sink.
Phil.

8
Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: April 26, 2019, 04:09:44 AM »
Yes I would like to know more about proper groundin g techniques. I have problems with stomp boxes because of poor grounding. Ugh
Well if you define your actual problem we will see if we can help :tu:
Phil.

9
Amplifier Discussion / Re: Vox Pathfinder 10 mods
« on: April 26, 2019, 04:05:31 AM »
j_flanders, I have only a crude understanding on filters, but in my simple terms, what I see with C5 is a high-pass filter, not a coupling capacitor.
The difference lies in the resistor (potentiometer in this case) in parallel with the capacitor, as it "leaks" the frequencies that can't get throught C5. What I did by changing C6 was allow more of these lower frequencies throught to the next stage.


Correct,, C5 is almost irrelevant for bass response going to U2, C5 is just a treble bleed for lower gain settings. C6 sets the low freq roll off point that gets to the next stage.
Phil. :tu:

10
Amplifier Discussion / Re: HELP Marshall 5203 Master Reverb 30
« on: March 09, 2019, 11:09:20 PM »
Another bad idea :duh

**IF** the circuit is not be designed to run at higher voltage then expect tears when the smoke escapes from the power amp :'( :'( :'(
Phil.

11
Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: March 09, 2019, 11:06:26 PM »
Answer; You just removed the ground loop. 8|
If you ground the case there are two ground paths which will cause hum. >:(
When looking at schematics the ground paths are hardly ever shown as they are all assumed.

Translating that drawing onto the actual circuit can be a challenge especially if you don't have a good understanding of ground paths.

I fixed a circuit years back and forgot one small fiber washer and hum was a problem.
I had created a ground loop as the fiber washer isolated the PCB from chassis.

i've seen reverb tanks where the rubber grommets had rotted away and gave intermittent hum problems as the tank would make contact with chassis as it vibrated.
Stuff like that can drive you insane if you don't know about grounding techniques.
Phil.

12
Amplifier Discussion / Re: HELP Marshall 5203 Master Reverb 30
« on: March 09, 2019, 01:25:25 AM »
No don't do that as you will exceed the voltage rating of the main filter caps which you say is 25volts.
Your transformer should have close to 15-0-15ACV which will reap 15 x 1.4 = 21VDC.

Never run Caps above the rated voltage otherwise they will fail. 8|
Always wise to have some head room as well so +/-21V rails leaves a few volts safety margin for the filter caps. ;)
Phil.

13
Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: March 07, 2019, 03:56:03 AM »
Check the reverb wiring, you may have re-connected the tank backwards which would induce the hum symptoms you describe.

Reverb circuits are normally wired with only the pickup side grounded to the Tank Case. (Not always but most often)

If the tank connections use RCA plugs then swap them over and see if the hum improves.

Input and Output are often marked on the tank case but some folks get them mixed up.
Phil.

14
Schematics and Layouts / Re: Ibanez TSA30 Schematic and PCB Layout
« on: March 06, 2019, 07:11:50 AM »
well you had me wondering as I noted a posting and then it was not there. :duh
Not to worry, in one sentence;
If you want lots of distortion then don't bother with NFB. :-X

The NFB of AB165 bassman is not going to work without major mods. you need those 220k resistors from the plates of power tubes. It was not a good design. :loco
(look up Rob Robinette site for lots of clues on what works and what is a waste of time)

I'm not a big fan of presence systems as you need NFB and that will run the amp cleaner so if you want lots of OD then you have to run the amp at much higher level.
If that is what you want then go for it.
If you just want more treble then lower the coupling cap in front of the PI stage.

Look at some fender schematics for clues,, a lot of the AB763 circuits have very small value caps at the PI input.

Those big fender twins are so loud due to the 1nF cap at PI input, Change that to 22nF and they would just fart out at high volume.
Remove the NFB and they would not be so clean at high volume. xP

Regards to Bassman,,, Which one???? :loco

Old valve amp schematics might look simple but you need to build a few to realise that a couple of changed values can make a huge difference. 8|

At the heart of most of them is the Power supply resistor values, they are often very different and that has a massive impact on the sonic result.

As example;
Your Amp circuit has R3 (22k/2Watt) now go look at most Bassmans and you will see they are 1k to 5k.
That alone makes a big difference as to how early the PI distorts.
Your circuit is closer to Plexi Values which means the PI OD's early.

Most Bassman's use AT7 while nearly all marshall's use AX7. Again that changes how the amp responds.

I could go on here as the options are endless but maybe you can just print out a dozen Schematics and look closely at the Power rail values.
Meantime read up Robs pages.
https://robrobinette.com/Amp_Stuff.htm

At 750 pages you might be there for a long time ;)

HTH, Phil.

15
Amplifier Discussion / Re: Help with Gallien-Krueger 200GT guitar amp
« on: March 02, 2019, 07:56:52 AM »
Well obviously there is an issue with the limit control system and as *Tonyharker* has noted it's likely simple.

clues;
I would think that the Limit leds should only light up when the signal reaches the set threshold. maybe a short flash at power on until the voltages settle but as they all come on then something is wrong around Q26.
So check the voltages around Q26,, all the test voltages are on the schematic.
Check you have -9VDC at ALL points marked (H). See if that voltage changes over time.

Namely points (H) at
Q3 & Q4
Q10 & Q11
Q23 & Q24
And also Q15 & Q16, the trem circuit.

My first suspect would be that Q26 has a problem,, maybe the Zener diode (D3) has died.

At Q26 also check you have -8.4VDC at points (G), as Q26 also supplies the neg rail for the whole preamp section.
HTH, Phil.

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