Fender 1975 twin reverb silver face, master volume push/pull circuit identification

[The Quadratus]

Hi all,

Hope you are all doing well.
I was hoping to ask the brains trust here about a bit of a query I have.

I have a fender twin reverb, dated to 75 (all the iron is 606-5-xxx).
Im trying to confirm which circuit I have, but, no schematic I have found shows what is going on in mine specifically and that has me quite confused. In particular V3, I've been looking at schematic AA270 and have the following similarities, discrepancies:

Pin 1-6 is jumpered, like my amp, pin 4-5 is jumpered, just like my amp. Pin 3-8 is jumpered, just like my amp. Pin 2-7 is jumpered, just like my amp. The schematic shows a capacitor on the eyelet board, in parallel with a resistor (cathode bypass I'm assuming) going from pin 7, mine has no capacitor. The difference my amp has is a capacitor going from pin 1 to pin 8 (560pf ceramic disc type) and then goes to the eyelet board with no capacitor on the board to ground.The resistor is there as per the schematic.

Want to understand which circuit I might have so I can order caps etc to refurbish it, still has the Mallory caps in the dog box and carbon resistors, one just cracked in half when I looked at it

Any help would be appreciated.

Thank you to anyone who responds.

[sluckey]

Quit looking at the AA270. It has no master volume! Look at one of these schematics instead...

https://el34world.com/charts/Schematics ... _schem.pdf
https://el34world.com/charts/Schematics ... _schem.pdf

[The Quadratus]

Quit looking at the AA270. It has no master volume! Look at one of these schematics instead...

https://el34world.com/charts/Schematics ... _schem.pdf
https://el34world.com/charts/Schematics ... _schem.pdf

Oh my god, I see the 560pf capacitor on the V3 tube!!!!
I will have to print this off and mark off exactly what I see to confirm. Thank you so much mate.
Which circuit would this be "officially" named?
Want to buy recap kits etc.

Thank you so much again

[sluckey]

Which circuit would this be "officially" named?

That info is on the schematics. Those schematics cover several models.

[The Quadratus]

Which circuit would this be "officially" named?

That info is on the schematics. Those schematics cover several models.

100w master volume. Got it was thinking it had similar designations to the previous circuitry AB763 etc etc.

Again, very appreciated.

[Stevem]

Please note before you purchase a re-cap kit that they only come with the electrolytic type caps that the amp has in it, they do not come with any coupling type caps or Ciramic disc type caps that are in the amp.

There are 3 non electrolytic type caps in the amp that you should replace because there known to go bad at times.

These are the 3 in the amps tremolo circuit that I have circled.

[Ten Over]

These might be of use to you:

Twin Reverb 75 Late AB763 Style.png

Fender Twin 100 1975 Layout.jpg

[The Quadratus]

Please note before you purchase a re-cap kit that they only come with the electrolytic type caps that the amp has in it, they do not come with any coupling type caps or Ciramic disc type caps that are in the amp.

There are 3 non electrolytic type caps in the amp that you should replace because there known to go bad at times.

These are the 3 in the amps tremolo circuit that I have circled.

Thank you so much man, it genuinely is appreciated. This community is
I have the blue ITW branded caps, that look like the orange drops..... Except blue I've heard they're not so bad in terms of values and drifting? Every other cap (and resistor it seems now) is going to get replaced.

[The Quadratus]

These might be of use to you:
Twin Reverb 75 Late AB763 Style.png
Fender Twin 100 1975 Layout.jpg

Mate........ I can't tell you how appreciated this is.
Was pouring over the rev g schematic and couldn't reconcile the v5 pin 7 connection with my amp's circuit. Had bits of the 135w schematic on my circuit that just didn't make sense.......

The drawing and the schematic you just provided are, well, saved me a lot headaches.

I cannot convey how thankful I am for this.
Thank you sooooooo much.
The drawing is identical to what I have on my circuit.

[Stevem]

To me the with what you have have there I would only replace the plate load resistor to start off with, as these carbon resistors when they go bad produce a bacon frying sound in the audio and they will add even more hiss.
I would replace them with 1 watt metal film types and the two on the PI section plates I might go up to 2 watt types.

It’s rare in these era Fenders, but when the the 68k resistors on the input jacks go bad they produce a ton of hiss when you have something plugged in and the switch built into the jack is open.

This is a critical place to use a metal film type resistor.

[The Quadratus]

To me the with what you have have there I would only replace the plate load resistor to start off with, as these carbon resistors when they go bad produce a bacon frying sound in the audio and they will add even more hiss.
I would replace them with 1 watt metal film types and the two on the PI section plates I might go up to 2 watt types.

It’s rare in these era Fenders, but when the the 68k resistors on the input jacks go bad they produce a ton of hiss when you have something plugged in and the switch built into the jack is open.

This is a critical place to use a metal film type resistor.

Thank you so much for your input. So far, the resistors on the input are reading fine.
Every other resistor has drifted a lot. I have been reading on getting metal film resistors (Vishay) and upping the wattage on all of them.

Appreciate your input, Steven.

[The Quadratus]

These might be of use to you:
Twin Reverb 75 Late AB763 Style.png
Fender Twin 100 1975 Layout.jpg

Would you happen to know where I could find a BOM for this?

[Stevem]

I am not 100% sure, but I think it’s highly unlikely that you will find that or have someone supply you with that .

[martin manning]

"If you give a mouse a cookie, he's going to ask for a glass of milk."

[nuke]

I have only occasionally seen the tremolo oscillator capacitors go bad in Fender amps. The 70's era film and ceramic caps are usually good and stable.

The electrolytic capacitors though, would be ripe for complete replacement. That means all the dog house caps, the filter caps in the bias supply and all the cathode bypass capacitors.

I'd recommend troubleshooting any problems the amp might have first, then proceed with the electrolytic re-cap.