Guitar Amp Capacitor Identification

[KeepItSimpleStupid]

Good points. Low current contacts are very fussy. Usually the material of the contacts allows it to function at low currents. Wiping can remove the oxide as well, but so can a current around 10 mA. 10 mA isn't likely with an audio signal.

 

[Cicero]

Hi again, appreciate the responses.

I don't come from the valve era, granted, and I'm more than willing to concede I have no idea what I'm talking about. I'd just like my guitar amp to work, haha.

What I meant by switching back to the rhythm channel. I mean using the selector switch. If I switch back again the lead channel is still dead. It won't come back until it's cooled down.

I haven't had much time to properly trouble shoot, checking signals and whatnot, but I did run a soldering iron along the majority of joints as my first instinct was a connected cold joint which disconnects when the amp heats up. Again without checking levels this was a blind exercise though. Well first thing I did was swap the valves, when that didn't work I tried a blind solder touch up.

 

[KeepItSimpleStupid]

This thing is an amplifier, so inject and trace. Binary search. I verify the beginning, then the middle, then half of that etc.

So, unless your re-capping for another reason, I'd say troubleshoot.

 

[Cicero]

This thing is an amplifier, so inject and trace. Binary search. I verify the beginning, then the middle, then half of that etc.

So, unless your re-capping for another reason, I'd say troubleshoot.

Yeah, that's a good idea. I just want to be proactive and buy some replacement caps just in case, so if it does turn out to be the problem (however small a chance it seems ) I don't want to wait to source a new cap. I only have a few days to get it all fixed and sorted, then I'm back in the UK again, another 6000miles away.

 

[KeepItSimpleStupid]

I remember guessing what I would need to build a safety system. I was designing and building "on the fly" per bosses request. They only got my notes. No real documentation. Your supposed to design, then order, build, test and make ECO's. My boss was dysfunctional with me. he really wanted me to fail, but I didn;t. They lost. The system was not likely to break either.

Not having anything to go on is tough. Not having any parts is also tough. In the valve era, resistor capacitor substitution boxes were common place. i.e. https://www.jpmsupply.com/Resistor-Substitution-Box-Kit-Elenco-K-37-p/80117.htm

The www.banggood.com component tester that Nigel likes and was reviewed on ETO would also not be bad for your collection. It's too cheap to pass up.

 

[Nigel Goodwin]

Seems like it would be easy enough to isolate the faulty stage with a scope.

This is a crude valve amp, a scope is a bit of 'over kill' - mostly all you need to signal trace is a screwdriver and a finger

 

[chemelec]

Based on your Post #22, I would really Suspect a COLD SOLDER JOINT on the PCB!

 

[Supgal]

Hi!

Could you please help me to identify two capacitors on the picture below attached.
I'm interested in the the gold flat axial on the left and the white flat axial on the right near the philips mustards.
**broken link removed**

Thank you for your help!

 

[chemelec]

Look like polystyrene caps

 

[Les Jones]

Do you expect us to be able to read the writing on those two capacitors from that picture ?

Les.

 

[Supgal]

No. Of course not.
I would like to know only the type and manufacturer.
Maybe a member of the forum has met them already.

 

[chemelec]

Possibly made by "Phillips".
Really Quite OLD.

 

[spec]

Just my two cents worth about capacitors (I am not saying that capacitors are the fault):

In general, you can fit polypropylene capacitors, with safety and good performance, to most amplifiers, especially valve amplifiers, and many other circuits.

As a very general rule your capacitor choices boil down to:
(1) Aluminum Electrolytic for polarized high value capacitors, both high current and low current types.
(2) Polypropylene metal film for general use
(3) Ceramic X7R dielectric for decoupling, but not in audio amps or any other low distortion application. https://en.wikipedia.org/wiki/Ceramic_capacitor

For non-critical applications you can use polyester metal film capacitors in place of polypropylene to save money.

And about resistors:
(1) Metal film are the best for normal resistors, but solid carbon may be required for high frequency work.
(2) Wire-wound for power resistors, unless it is essential for frequency performance to use carbon or ceramic power resistors

Metal oxide resistors are the most reliable, and can be used in place of metal film but not for low distortion applications.

spec

 

[Supgal]

Thank you chemelec, you drove me in the right way.
The gold one is old siemens film cap.

hi spec,
thanks for the clearification!

 

[spec]

hi spec,
thanks for the clearification!

No problems Supgal.

spec