SF twin reverb 135 watts needs refurbishing.

[g1]

The 1N4007 will be fine for rectifier and bias.
If you are keeping the Acc. AC socket, check the polarity, they are sometimes wrong. It helps to use a meter as it can be very difficult to see which screw goes to which terminal.

[g1]

Here are a couple layouts that have been edited. I'm hesitant to post them as I believe there may have been errors. So use them as a guide but not as gospel, verify any discrepancies.

[nevetslab]

I haven't seen a 135 MV schematic with a layout. This is the schem and layout that is closest to my 100W MV Twin, maybe it is similar to the 135W.

Here's my Fender SF 135W Twin Reverb Schematic: twin_reverb_sf_135_schem.pdf

[pdf64]

From the photo, it looks like the main speaker socket has taken a bash.

[Tom Phillips]

Here's my Fender SF 135W Twin Reverb Schematic...

That's the schematic I have too. There, does not seem to be a companion layout available but I find that the layout is very similar to the original twin reverb. You just need to follow the schematic to troubleshoot the ultra linear output section and the speaker impedance switching circuitry.

[rockman627]

Sorry too take so long. I had sciatica and was out for a week. In any event I'm back and back on the case. I'm waiting for parts then I'll rebuild the filter cap section, rectifier section and bias voltage section. I've already bypassed the ground switch , keeping the a.c. outlet. A few questions though. The rectifier diodes look like little beads. The tiny little line on one side still indicates cathode, correct? Also I have a dual bias probe. Whenever I bias a twin, I put tubes in only V9 and V8, measure plate voltage and bias to about 50%. I take note what the bias currents are, then pull the tubes and repeat exactly for the next two tubes. Then I try to place the tubes so V10 + V9 are close to V8 +V7. Is this a good method?

[Tom Phillips]

..The rectifier diodes look like little beads. The tiny little line on one side still indicates cathode, correct?...

I suggest you follow the rule of "Diagnose problems before replacing parts." This will save you time and, in some cases, prevent causing new issues. Those rectifier diodes are not known as a weak part of the design so I would not be replacing them if there is no direct evidence that they are bad. You can easily test them in circuit using the diode test function of your DVM. Furthermore, there is nothing in your previous posts that suggests any rectifier issues.

[rockman627]

It seems to me that if I'm going to replace the accompanying disc caps, I might as well put in some fresh diodes. Are the original diodes that good?

[Helmholtz]

I've already bypassed the ground switch ,..

I hope you didn't really bypass the ground switch.
Rather it should be disconnected and the cap removed.

[Tom Phillips]

It seems to me that if I'm going to replace the accompanying disc caps, I might as well put in some fresh diodes. Are the original diodes that good?

I would not expect to replace those disc caps either.
The diodes don't just wear out or get weak. A primary mode of failure is that they short out and, if that were the case, your amp would be blowing the mains fuse.

[The Dude]

I suggest you follow the rule of "Diagnose problems before replacing parts." This will save you time and, in some cases, prevent causing new issues. Those rectifier diodes are not known as a weak part of the design so I would not be replacing them if there is no direct evidence that they are bad. You can easily test them in circuit using the diode test function of your DVM. Furthermore, there is nothing in your previous posts that suggests any rectifier issues.

Amen!

[g1]

Your bias method will work, but no need to pull 2 tubes at a time. Run all 4 and check 2 at a time with bias probe.

[The Dude]

In fact, not only no need to pull 2 tubes, but makes no sense. B+ will be lower with all tubes installed than with only 2. You want to bias in operating condition.

[rockman627]

Yes I removed the wires from the ground switch. Black wire went straight to the fuse and white straight to the transformer. And thanks for the info about the bias and rectifier.

[rockman627]

I had some time today so I rebuilt the filter cap board. I guess I did it right as the caps did not explode and the fuse didn't blow. I would like to address the hum balance next. If you look at my first photo, the hum balance pot is below V2 . There are resistors going from the pot casing to V2 pins 4/5 and 9. There are 2 wires hanging from the pot unconnected to anything. Some diagrams have the middle post connected to ground and a wire from 1 post to V2p9 and the remaining post connected to V2p4/5. This makes sense to me but before I do it I want to ask if this is right.