low voltages with 5y3 and fender original 5e3 PT

[pietro_moog]

hi guys. i built a sort of 5e3, with the 5y3 and the fender original PT, which is rated 325-0-325. i was expecting something like 360v out of the rectifier, but i measured just 308v. everything is good, the amp works. how comes?
i tried my gz34 and i see around 370v. my meter is good. the voltage on the wall is 230v. i don't understand..

[Tom Phillips]

hi guys. i built a sort of 5e3, with the 5y3 and the fender original PT, which is rated 325-0-325. i was expecting something like 360v out of the rectifier, but i measured just 308v. everything is good, the amp works. how comes?
i tried my gz34 and i see around 370v. my meter is good. the voltage on the wall is 230v. i don't understand..

You are correct to expect higher B+ with a 5Y3. First thing to try is another 5Y3. Have you done that?

You said that the transformer is "rated" 325-0-325. Have you actually measured that? I doubt that low output from the PT is the problem since you get 370 Vdc with the GZ-34 but it's always good to know the actual readings.

[pietro_moog]

i measure now 635v across the PT secondaries. and i have 323v on pin 8 of the rectifier. unfortunately i have just one 5y3 for now

[pietro_moog]

tried my gz34. 604v across the PT secondaries and 354v on pin 8. 216v ac on the wall.
i don't understand

[Jazz P Bass]

You can't get something for nothing.

Your 5Y3 has a lower output, therefore there is less of a draw on the PT secondary & the secondary voltage is higher.
That does not mean that it is bad, it is simply lower.
Most probably the cathode is limiting the output.
If it is an old tube, that makes sense. It is wearing out.
If it is a new tube, that also makes sense as it seems current tubes are being made by idiots.

The 5Y3 would be good for making an amp 'Brown'.

[pietro_moog]

cathode? you mean the cathode resistor? i have a bigger one, 390Ω instead of the 250Ω in the schematic. do you think it is a problem?

[Jazz P Bass]

No, not the cathode resistor.

The cathode inside the rectifier.

The electron emitter.

[pietro_moog]

ok. so what i'm getting is: the amp is fine. the PT is so-so, the rectifier is crap. ok.

[Tom Phillips]

ok. so what i'm getting is: the amp is fine. the PT is so-so, the rectifier is crap. ok.

You are likely correct on all counts. It could also be that one half of the 5Y3 is dead which would mean that you are only getting half wave rectification. That's just a guess but it would cause lower output under load. Your low wall voltage will also contribute to a lower B+ reading.