70's valve guitar amp needs TLC

[Galu]

Hold off on ordering capacitors till we sort out the wiring problems. If the bottoms of the capacitors are not bulging or leaking then they are not in urgent need of replacement.

 

[PRR]

...the 100k anode resistors and all read around 102k - is that ok or too far out of tolerance? ...

What does the gold band mean?

I had a long essay about the history of 20% 10% 5% tolerances in guitar amps but the internet ate it.

 

[ammers2]

OK Galu I will hold off doing anything until we have some more info. Do you know people or are we waiting for a chance visit by someone on this site? Either way, once again thanks for your help

Steve

 

[Malcolm Irving]

... Looks like the free end of the 56k should go straight across the tag strip then attach to the 16 ohm tap on the output transformer via a missing length of wire.
....

Yes, that looks consistent with the information available.

 

[Galu]

Thanks Malcolm!

OK ammers2, we have a second opinion. Can you identify the wire we are talking about on the attached photo?

It runs from the 56K resistor down to the 16 ohm tag on the loudspeaker impedance selector. This wire is missing from your amp and you can try replacing it.

It would appear that the previous owner has removed this feedback loop in order to increase the gain of the amplifier. Just say if my instructions are not clear.

 

[ammers2]

Hi guys

Is it the one inside my crudely drawn orange boundary? If so I will give it a go. Any particular wire to use??

Steve

 

[Galu]

That's the one. Wire not critical - just match up with what's elsewhere in the amp.

Observe safety precautions when testing the amp!

 

[thoglette]

What does the gold band mean?

5% Had to check - I would have said 10% from memory. See wikipedia.

 

[PRR]

...I would have said 10% from memory.....

That was for ammer2's self-education. But if it jogged your mind, that's cool.

 

[thoglette]

That was for ammer2's self-education. But if it jogged your mind, that's cool.

The moment I hit "submit reply" I thought - oh, wait, perhaps that's not where PRR was heading.

 

[Kay Pirinha]

PRR has nailed it. He also could have said: »You're showing such a profund lack of basic knowledge. So it most probably will be better for your health to keep your hands off any electronics' innards.«
Best regards!

 

[ammers2]

Just to make sure I do this right. Should the new wire from resistor be soldered to tag on the rail first and then follow on diagonally to 16ohm tag or can I just send wire straight across to said 16ohm tag?? There is no solder residue/evidence of previous connection on the tag on the rail?

 

[Malcolm Irving]

I would solder to the spare tag to give some mechanical support.

 

[ammers2]

Thought ‘d just add photo of the 16ohm tag. It appears to confirm your findings don’t ya think?

 

[ammers2]

P.s. normally set to 8ohm for the celestion drive unit.

 

[Galu]

I presume the black wire goes to the 16 ohm tap?

It does appear that a wire has been cut off the top of the tag, but I can't be certain from your photo.

 

[ammers2]

Hi Gali not sure which post of mine you are replying to but in last photo the white cable goes to 16ohm tag. You can see at solder joint where it has been cut. PLease ignore speaker plug it is set in photo to 16 but should be up/ down set to 8

 

[ammers2]

Sorry Galu not Gali

 

[Galu]

I was replying to post #34. I can't see the settings, but you appear to be on the ball!

 

[nigelwright7557]

Old amps suffer from dried out electrolytics which lose value.
Or sometimes even go short circuit.
After that the things that age are mechanical contacts.
Sometimes soldered joints go dry especially on larger items.