JC120 +15 supply issues

[Enzo]

I have never seen a bipolar TO220 that was not BCE across the front. This is only a basic power supply, so ANY NPN of sufficient voltage and current ought to work.

If the unloaded thing only puts out 4v, then I wouldn't waste time looking for loading. Change the transistor.

The transistor diode test finds bad transistors, but they can easily be bad in other ways. How do I test them? By their performance in circuit.

Never seen anything like this? This is just a very basic zener regulated power supply. Should be covered in any power supply tutorials.

[Mr_bibbles]

I have never seen a bipolar TO220 that was not BCE across the front. This is only a basic power supply, so ANY NPN of sufficient voltage and current ought to work.

If the unloaded thing only puts out 4v, then I wouldn't waste time looking for loading. Change the transistor.

The transistor diode test finds bad transistors, but they can easily be bad in other ways. How do I test them? By their performance in circuit.

Never seen anything like this? This is just a very basic zener regulated power supply. Should be covered in any power supply tutorials.

G1, Gonz, Bill, Enzo, thanks for all your help! It was the q27 pass transistor. 15+ is up an running all across the amp, chorus and reverb sound dreamy. And by "haven't seen anything like this", I meant this issue in this particular amp! I'm self taught, which means I have huge gaps in my education and forums like this are the only place I can turn to for real world help.

I can't express my appreciation enough, you guys really have given me a way of life- I first came here years ago without understanding even the basics, and now I'm at a point where I can misunderstand the basics on an advanced level. Cheers!

[Jazz P Bass]

"I first came here years ago without understanding even the basics, and now I'm at a point where I can misunderstand the basics on an advanced level"

Beautiful!

[Enzo]

I don't think in terms of particular amps. A zener supply is a zener supply, and it doesn;t matter what amp it is in. Whether I ever saw this particular zener supply failure in a JC120 or not is not in my memory.

[DrGonz78]

I feel the need to say that I should have questioned Q27 more in my first response. In thinking about the symptoms I was on the fence about the fault being Q27 or something downstream. If it was downstream then I imagine that even the zener diode 15v would be dragged down too.