'65 Fender Champ No Power

[ca7922303]

There are a few ways to drop voltage with the existing PT. But first, is the 5y3 a Sovtek brand tube?

GE GZ34

[ca7922303]

GE GZ34

Transformers

[Helmholtz]

GE GZ34

Wrong rectifier tube.
With correct 5Y3GT B+ should be around 40V lower.

[Helmholtz]

Transformers

PT is correct.

[Chuck H]

But high supply voltages won't cause low output.

Ah, but... Since the preamp in an AA764 doesn't clip and the class A power tube can't be center biased this might have an influence. I did interpret anemic output to mean "Champ". Which means low output anyway. But I also "no clipping". Which I also interpreted as part of a possible misdiagnosis simply because the power tube wasn't clipping. I thought it was possible the lack of clipping was the main culprit for the description of the weak sound.

[Chuck H]

Well this might have been easier. See post 15


We've been diagnosing with incorrectly reported or possibly changed circumstances. Why?!?

Like Helmholtz said then. Put a 5y3 in the amp. Leave the 470 ohm cathode resistor in place.

[ca7922303]

Well this might have been easier. See post 15


We've been diagnosing with incorrectly reported or possibly changed circumstances. Why?!?

Like Helmholtz said then. Put a 5y3 in the amp. Leave the 470 ohm cathode resistor in place.

So is it safe to guess that if 5y3 drops 6v6 down to 399v, I should notice even more output and clipping?

[Helmholtz]

So is it safe to guess that if 5y3 drops 6v6 down to 399v, I should notice even more output and clipping?

Rather somewhat less output and a bit more clipping.

You need to measure output power.

If 6V6 grid drive is healthy and output is really low, you might have a bad OT.

[Chuck H]

If 6V6 grid drive is healthy and output is really low, you might have a bad OT.

I didn't know they ever had good ones

Functional, maybe, but all Champs with a tone stack and the stock OT sound "weak" to me. Of course I agree about measuring output once the amp is put right otherwise. Maybe just my opinion but I would consider a bad OT a mixed blessing. Extra expense, yes. But also an opportunity to greatly improve the amp with an upgrade.

[ca7922303]

So, installed new JJ 5Y3 rectifier tube and 6V6 now reads(395v), notice more clipping and not much volume difference to my ears. 6V6 is a GE and 12AX7 is a RCA. GZ34 was also a GE. Serial number winds up being a '66.Thsnks for the help.

[glebert]

Seems like at this point you could measure output power at the speaker with a sine input and see how much you are getting.