Brown Face Fender Bassman Approximate age?

[jshag]

First Looking for approximate age since inside tube diagram is gone for all practical purposes.
Chassis stamp is BP06515 if that's any help. It is in a black tolex cabinet, could have been swapped.

Looking for schematic or quick wiring diagram of power transformer. I am getting heater voltage (6.6VAC) But no HT voltage.
Going to see if winding is open as it's not blowing fuses. Wold like to know where attachment points are so I can separate xformer from circuit.
Thanks

[The Dude]

Tube or solid state rectifier? Either way, I guess, you should be able to ohm the HT secondary without unhooking it. It's obviously not shorted or you'd be blowing fuses. Just find where the transformer wires feed the HT rectifier and ohm it out.

That said, these things rarely fail. I'd be more apt to believe you have a bad standby switch, rectifier tube, or something of that sort.

[jshag]

solid state rectifier 345VAC in 200VDC out.

[Justin Thomas]

Presence control? Because if it IS a brownface in a black cab, bet it's a 6G6-B. The Bassman was a slow evolver... the last of the "white" Nassmans went in black cabs. So if it's really a brownface (& not a dirty blackface), call it a 62/63 transition model. Presence control & barrel knobs are a giveaway. No presence control, call it an AA864.

Agree with Dude on "tranny is last suspect on list."

Justin

[The Dude]

solid state rectifier 345VAC in 200VDC out.

Is this measured or where did the numbers come from? I thought there was no HT voltage?

[jshag]

My mistake. Those are actual readings off the rectifier board. Just going to go through each stage like normal. Sometimes there are no shortcuts Transformer seems to be okay.
Brown face chassis has cream colored knobs, two channels with a presence control.

[The Dude]

That voltage is way low if measured correctly. What is/are your symptoms? What's wrong with the amp? At this point I'm suspecting bad filter caps given the low DC. How much AC do you have on the HT supply?

[jshag]

No audio output is primary symptom. Filter caps all have the beginning of a nipple at the positive side.
Just noticed black stamp mark DEC 2963 on wiring side of chassis. Could be Dec 29th 1963?
Visual inspection show gunk outside TR 2 125C1A. It is connected to standby switch output. Measures 100 Ohms in circuit.

[The Dude]

That part is a choke and should be fine. Let's back up here. First you said no HT and then measuring at the diodes you found HT. Albeit low, can you verify that you have ANY HT voltage to the tube sockets and that your standby switch works.

[jshag]

No HT Voltage to tube sockets. Standby switch checks out. Curious as I am reading 200VDC on standby switch when it is engaged I watch the reading go down to zero. (-0.8VDC)

[The Dude]

Does the voltage go down on BOTH sides of the switch or only the side connecting to the OT?

[jshag]

Voltage goes down on both side of switch when in on mode

[The Dude]

Ok, seems like we're going in circles here. The standby switch should connect directly to the output of the HT rectifier where you said you got 200VDC output. I assume that goes to 0VDC also then? What happens to the AC feeding the rectifier when the DC drops?

[jshag]

Sorry for the circular path here. And thank you for your help and interest.
Yes HT feed to stand by switch also goes to 0VDC. The output measured at the switch and the output of rectifier both go to zero and now on power up are almost at zero to begin with.
Input to rectifier remains at 345VAC both legs.

I have been draining caps by unplugging AC and shorting pin 1 of preamp tube #1 to ground.

[Enzo]

And is the center tap of the HV winding not grounded?