Fender Silver Face Pro Reverb

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Fender Silver Face Pro Reverb

Postby RobW on Tue Nov 08, 2016 8:47 pm

Hi I would appreciate any help.

Repairing a late 70s Silver face Pro Reverb with master volume. It has a ultra linear output transformer. The power supply delivers about 188 0 188 AC on the power supplies secondary winding, delivering a B+ of 252DC. The schematic does not say what the secondary AC voltage should be just that there should be 500 DC at the standby switch, I get half that. Does this amp have a voltage doubling circuit? The centre tap from the mains transformer is connected to between the reservoir capacitors which are 200uF not earth so it could be but I'm not sure I've never come across this circuit before. I have looked for the exact mains TX and according to the spec it should be delivering 190 0 190 AC as this one does.

Any help appreciated.

Rob :)
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Re: Fender Silver Face Pro Reverb

Postby Dean Jr. on Tue Nov 08, 2016 11:12 pm

You should be looking at something like this for that amp---see below.....over 300VAC on each leg of that secondary feeding the rectifiers. I don't know where you got that 190-0-190VAC spec. Your amp has some problems. I would lift the B+ feed from the filter cap section. IF that still looks bad, I would lift the red secondaries from the rectifier and see what is coming from the PT.


http://www.classictone.net/40-18029.pdf

http://www.hammondmfg.com/pdf/EDB290DX.pdf
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Re: Fender Silver Face Pro Reverb

Postby stratele52 on Wed Nov 09, 2016 9:40 am

Which schematic do you use, any link ?

Pro reverb Ultra linear here;
http://bmamps.com/Schematics/fender/Pro ... linear.pdf

Before working on a old amp, check if the fuse is the right one. Too many people put a too powerful fuse and power transformer may burn.
Be careful, lethal voltage in tubes amps can kill you

Low B+;

1- No there is no voltage doubler
2-Check solid state diodes rectifier
3-Remove all tube, and check for a higher B+
5-Check heater voltage with and without tubes. you must have 6.3 volta AC or very close

Disconnect AC secondary from solid state rectifier and read AC volt from ground

Report all these reding
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Re: Fender Silver Face Pro Reverb

Postby RobW on Wed Nov 09, 2016 7:32 pm

Thanks to you both for your replies. Finally got there and got it working today at just over 500 volts now. I only found the problem by accident. The bus wire that runs under the sandwich board between the rectifier and the lug where all the B+ outlets are connected had burnt out. The 250 DC voltage I was seeing at the standby switch and that lug was from the transformer's centre tap which on this one connects between the two reservoir caps. I never tested at the rectifier outlet lug just the B+ lug next to it about 10mm away, it was showing 250 DC. It was due to your suggestions that I disconnected the B+ wires and found that there was no voltage at that connecting wire, thanks. I have my theory about it. When I received the amp to repair the voltage selector was on 100 volts not 240 as it should be here in Wales so the wire may have fused, thanks for the help.

By the way yes that is the schematic and the transformer is this one, http://www.tubeampdoctor.com/en/shop_Ma ... 70_75W_102

Rob :cheers:
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Re: Fender Silver Face Pro Reverb

Postby Dean Jr. on Wed Nov 09, 2016 8:10 pm

Good find.
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