Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - Tassieviking

#121
I would find clips on Utube and other places, read forums etc to find an amp I like the sound of, and then go from there.

I made a PCB for the Marshall 12watt amp because its popular and sought after, I posted the gerber files somewhere on this site for the PCB files.
If you are just after the pre-amp then you could easily build it on a Solder-less Plug-in Breadboard to try it out, change the tone stack and gain components etc.

How complicated do you want to go ? A simple pre-amp or multi channel pre-amp ?
What sort of power are you going to run it at and is it for home or are you going to use it in a band etc ?
#122
 Diary Of An Axeman:-
I forgot to say that I love to see photos of the insides of amps and pedals, if you could find it in your heart to open the pedal again and take lots of photos of the front and back of the PCB you might get other people to jump in and trace the schematic for you.

We just need to see the resistor bands and capacitor values etc, it can be a fun exercise to do a trace on old gear to get the schematic for it. Sometimes it's amazing how many variations there are out there.

I have done it a few times for SS amps myself.

Cheers
Mick
#123
I saw a schematic that someone traced from an original unit and it showed a 2Amp fuse.
I think that seems a bit large for a tiny transformer.
If it should be a 2Amp fuse it would be fast blow.

If I had any gear from the late 60's I would test and most likely replace any Electrolytic filtering capacitors in there.
At least test all caps to make sure they are still within specs and not shorting out.
If the 1000uF cap is playing up you could do some damage to that little transformer.

Even better would be if you traced the whole pedal and left a schematic here of what you find, there are a few variations out there with different value components in them.

Hmmmm....1968-1969,,,,, I think that's when I first started plucking strings on a nylon string guitar.




#124
Thanks g1 for pointing out that error in the file naming, I did not realise that that C was for the revision, I think I have fixed it on post 10 ok now.(and in my computer as well).
I would love to see revision E if you have it g1, it would be great if you could post it.
#125
700RB-11 Manual page 10 shows the 10Uf 50V NP capYou cannot view this attachment.You cannot view this attachment.You cannot view this attachment.
#126
I noticed that one variant of the 700RB-II power amplifier uses a 10uF 50V NP capacitor where your C21 is, perhaps your model should have a NP (NON-POLARITY) capacitor in there.
If the cap is polarized and gets fed a reverse voltage it would most likely smoke and pop like yours did.

Can you trace where the track goes to from pin 8 on the LM3886 ?
It most likely goes through a resistor to the negative supply voltage somewhere. (Mute 2) ??

Do you have the preamp schematic for the early 700RB ?

#127
If that is the correct schematic then Q6 is in a totally different part of the circuit, and J1 shorts the B & E legs on Q6.
Is Q6 in the main power amp section or in the circuit with the LM555 IC (U1)?
#128
Looks fantastic, nice tolex work. Is it red jungle bark tolex ?
#130
Honey Amp / Re: LTSpice sim?
June 23, 2023, 05:20:44 AM
Built what exactly ???
#131
If you used thermal paste on the transistor insulators, make sure that you are using non-conducting paste.
It is very common to use conductive thermal paste in computers and other places where there is no need for any insulation between the component and the heatsink.
Thermal heatsink paste is a big no-no in amps, I refuse to have any at home just in case I make a mistake one day.
Good quality paste and just a very thin film of it is all you need, if you have the cheaper stuff it will dry up and become useless faster the the good stuff.
#132
Could it be the TO-3 insulators, maybe you have a short from the power transistors to the heatsink.
#133
The 1N4744 diodes are ok at up to 175C (347F) temperature, but the power handling will be severely reduced.
At 100C (212F) the power rating drops in half to 0.5 watts (boiling water hot).
At 100F they are still working at 100% capacity, that's not even warm for a semiconductor.

The X in VX means nothing as far as I know, maybe the designer picked X because it feeds the effects (FX in shorthand) circuit. (Noisegate)
I'm guessing the CD4013 flip flop chip might be noisy when operating so they made a separate supply for it to reduce noise in the rest of the amp.
I think when the signal into U8 drops below a certain level Q4 and Q7 turn on, Q4 shorts the signal going into the octave unit and Q7 drops the gain in U6:B, ;that drops the signal right off.

Play with the clean channel gain when using the distortion channel and see if it affects the cut out level.
If I am wrong about that then I hope someone will jump in and correct me.
(I'm old school, I learn better if I get a clip over the ears so don't hold back).

I am wondering where you are picking up the test points, I can't see them on the layout.
Test point TP17 to TP19 voltage don't exactly match R42 voltage, but it should.
If you are measuring TP17 far away from R42 then I guess you could loose some voltage in the tracks but with only 34mA it seems strange to me.
Could there be some bad solder joints on JW7 or JW32 ? Maybe it is just the track loss but I would want to know if it was my amp. Measure voltage drop from D14 to R42 leads to find out.

G1 will lead you in the right path as I think he knows a lot more then me.

Cheers
Mick

#134
Amplifier Discussion / Re: Hartke HA5000 biasing
June 09, 2023, 12:16:08 AM
I can't see TP1, but I think I have the correct schematic.
#135
The noise gate is shown on page 7 of the user manual in the block diagram, I'm not smart enough to know how that works. =)

 Good photos Gonflable, I like being able to see what it looks like and sometimes a photo shows bad solder joints that we miss and others notice.

Something is not adding up with the voltages, TP17=21v, Vdrop on R42=8.6v, TP19=11v.
We seem to have lost 1.4v in those measurements.

Could you please measure TP18, TP20, Vdrop on R43, R46, R85  just for reference.
It would be interesting to compare the positive rail and the negative rail current drain.

I just noticed that the tuner and foot-switch circuit are all run of the +15v rail as well, this would add further load on the +15v rail compared to the -15v rail.

Just the distortion red LED would add more voltage drop to the +15v compared to the -15v rail.
Led = approx 8.3mA, 0.0083mA x 220R = 1.826v in R42, 8.3mA 47R = 0.39v in R45.
Surely the engineers who designed the amp would have realized this and made slight differences to the design.
Maybe I'm on the wrong path there but I would be wondering about tweaking the values of R42 to maybe 150R, but I would do it in small steps.
D18 is a 15v 1W zener diode, but it can't do anything if the voltage drop across R42 is less then 6v, it needs more then 15v to start conducting as far as I know.

Measure the -15v rail first and we will start to work it out, after all I could be completely wrong.