Does anyone need an extra 700 volts?

[gui_tarzan]

I just finished a build based on the 5F6 Fender Bassman schematic and I have no sound. I do however have an extremely high surplus of voltage on pin 3 of the output tubes and I'm not sure why. According to the schematic I should be seeing around 440v there but it's almost three times that.

I've been through my wiring a few times looking for mistakes but I just dont' see any. What in the world would cause that?

[ToneMerc]

I just finished a build based on the 5F6 Fender Bassman schematic and I have no sound. I do however have an extremely high surplus of voltage on pin 3 of the output tubes and I'm not sure why. According to the schematic I should be seeing around 440v there but it's almost three times that.

I've been through my wiring a few times looking for mistakes but I just dont' see any. What in the world would cause that?

1100+ volts at pin 3, it's the flux capacitor

TM

[gui_tarzan]

Heh... but seriously folks...

[ToneMerc]

Heh... but seriously folks...

Ok, so you used the standard power transformer and wired it as indicated on the layout? If so, are sure that your VOM is accurate?

TM

[gui_tarzan]

I tried two different VOMs, a good one and a cheap backup unit and they read identical voltages. The transformer is out of a DuKane intercom amp that came with a 5U4 rectifier, a 12AT7 and two 5881 tubes. The B+ red leads read 365v to the CT and the yellow leads are 5v and both sets go to my 5AR4C rectifier tube.

The first cap reads 500v after a few minutes (it starts at 585v and drops to 500v) and the positive lead on the second cap reads 1192v. That's WAY too high.

[Leo_Gnardo]

The first cap reads 500v after a few minutes (it starts at 585v and drops to 500v) and the positive lead on the second cap reads 1192v. That's WAY too high.

Def. something goofy going on here. IF you really had nearly 1200V I think the second cap would have gone up in smoke by now.

[ToneMerc]

I tried two different VOMs, a good one and a cheap backup unit and they read identical voltages. The transformer is out of a DuKane intercom amp that came with a 5U4 rectifier, a 12AT7 and two 5881 tubes. The B+ red leads read 365v to the CT and the yellow leads are 5v and both sets go to my 5AR4C rectifier tube.

The first cap reads 500v after a few minutes (it starts at 585v and drops to 500v) and the positive lead on the second cap reads 1192v. That's WAY too high.

So just to confirm, you wired the rectifier as indicated below?

http://www.ceriatone.com/images/layoutP ... iatone.jpg

TM

[gui_tarzan]

Yes, but the Fender schematic doesn't show the resistors or that cap. And why are the two 20uf caps wired parallel instead of serial? That gives it 40uf but still only 600v, correct?

[gui_tarzan]

A 5Y3 rectifier shows the same voltages at the caps.

[ToneMerc]

[quote="gui_tarzan"]Yes, but the Fender schematic doesn't show the resistors or that cap. And why are the two 20uf caps wired parallel instead of serial? That gives it 40uf but still only 600v, correct?[/quote

Most likely because 60 yrs ago there was not a widespread range of values, so you paralleled two 20ufs to makes a 40uf. I tend to follow Fender's later design of using caps in series with 220K balancing resistors. For example, using two modern 80's in series to get 40uf.

TM

[ToneMerc]

The first cap reads 500v after a few minutes (it starts at 585v and drops to 500v) and the positive lead on the second cap reads 1192v. That's WAY too high.

Def. something goofy going on here. IF you really had nearly 1200V I think the second cap would have gone up in smoke by now.

I agree Leo for a PT that's supposedly, 365-0-365

TM

[gui_tarzan]

And that's exactly what I did. A 220K across each cap, caps in series to make 40uf & 900v. The PT measures 820v end to end, 410 to the center tap. The cap board is actually the one I put together for my Bassman 100. Do you guys think the PT might be too much for this? I guess I can try a different PT, but I was hoping this would be a good one for this amp.

[Blindog]

Yes, but the Fender schematic doesn't show the resistors or that cap. And why are the two 20uf caps wired parallel instead of serial? That gives it 40uf but still only 600v, correct?

Yep, in parallel you get 40uf, 600V. If they were in series, the voltage rating would increase, but you would only have 10uf

Mark

[gui_tarzan]

Right. I have two 80uf/450v in series so that's 40uf/900v.

[Blindog]

Right. I have two 80uf/450v in series so that's 40uf/900v.

Yep! Oops, my page didn't refresh, Tone Merc had already answered, my other post wasn't necessary