Bassman 5F6-A voltage check

[DC Music]

Hi guys,

I'm just after a quick check on some voltage readings I got for a home-built Bassman, circuit 5F6-A. NOS Sylvania "Fat Boy" 5AR4 rectifier. I'm unsure of the power tubes, they are stamped RCA but they are brown-based 5881's so I'm guessing Canadian GE's or similar? I don't think they're matched. I'm able to bias them to get 35mA at V4 and 31mA at V5.

Wall voltage is 242VAC
B+ at standby switch = 470V
Heater voltages 6.7VAC

V1
Pin 1 - 110.3
Pin 3 - 1.87
Pin 6 - 113.5
Pin 8 - 1.87

V2
Pin 1 - 123
Pin 3 - 0.82
Pin 6 - 225.2
Pin 7 - 123
Pin 8 - 124.5

V3
Pin 1 - 285.3
Pin 2 - 25.15
Pin 3 - 41.2
Pin 6 - 274.1
Pin 7 - 26.87
Pin 8 - 41.2

V4
Pin 3 - 470
Pin 4 - 470
Pin 5 - (-)45.9
Pin 6 - 470

V5
Pin 3 - 470
Pin 4 - 470
Pin 5 - (-)48.5
Pin 6 - 470

V6
Pin 2 - 470
Pin 4 - 372VAC
Pin 6 - 372VAC
Pin 8 - 470
Heater (2 & 8) 5.31VAC

Filter caps
A - 470
B - 470
C - 431

Do you guys think these are healthy numbers?

[Enzo]

Probably.

You get it to bias up to a reasonable setting? And the amp sounds OK?

Then it works.

[loudthud]

Voltages look acceptable. Although they are not what you see on the Fender 5F6A schematic, I don't see anything to indicate a bad tube or wiring error. V2 pin 8 looks a little on the low side. The voltage on pins 2 and 7 of V3 will not measure correctly because the meter changes the bias on the phase inverter while you are taking the measurement.

[DC Music]

Thanks for the replies guys, I appreciate it.

[DC Music]

Probably.

You get it to bias up to a reasonable setting? And the amp sounds OK?

Amp sounds great, very much like a Bassman!

[MWJB]

Your preamp voltages at V1 & V2 are low, very low. What tubes do you have in V1 & V2, if 12AX7 I'd expect over 200v on the plates of V1. Even if you had 12AY7 in V1 & V2 I'd espect more like 170vdc+ on the plates.

If you have used a larger than 10K preamp drop resistor, maybe for harp use, then that may explain the readings?

You mention filter caps A, B & C...if that is B+, screens & PI, what is the reading at the preamp filter (usually mounted on the board, next to the 10K preamp drop resistor)? Should be ~350vdc.

[DC Music]

Turns out I had a couple of mis-labelled bags of resistors. The 10k, 1watt bag was actually filled with 47k, 1watt. So my preamp drop resistor was too high! Problem solved.

Thanks again for your advice everyone.