Possible layout error

[sergio]

In this layout the cathod resistors of reverb are inverted.

The right wiring are: 820 Ohm for Driver and 2k2 for Recovery.

[Normster]

I'll let Gary weigh in on this, but Fender, Mesa, and Pignose all used 2k2 on the driver and 820R on the recovery side. FWIW, they also typically used 25uF bypass caps rather than 5uF. I should have Moss do some bias calcs to see which way is correct.

[Firestorm]

Blackface Fenders used 2K2/25uF on the driver. The only reason the recovery amp had 820/25uF is because the cathode resistor was shared by two triodes. Equivalent for a single triode would have been the stock 1K5 (they used 820 because 750 wasn't a standard value).
Late '70s Fenders used unbypassed resistors as low as 470 on the driver (the lost common value was 680), probably in recognition of the fact that the driver was being run for power, not for voltage gain. The 5uF on the recovery tube was a tweak to reduce stage rumble from the tank.

[Normster]

Blackface Fenders used 2K2/25uF on the driver. The only reason the recovery amp had 820/25uF is because the cathode resistor was shared by two triodes. Equivalent for a single triode would have been the stock 1K5 (they used 820 because 750 wasn't a standard value).

Doh! Of course it should be 1K5 with a 100K plate resistor. I can't believe I missed the obvious for so long. Now you've got me intrigued by the unbypassed 680R cathode on the driver. Since I'm only driving the tank with a single (un-paralled) triode, would that help me drive the tank better? Also, would 680R be correct for a single triode?

[Structo]

Does this circuit use any NFB?
Or is that what the accent switch does?

[Firestorm]

Doh! Of course it should be 1K5 with a 100K plate resistor. I can't believe I missed the obvious for so long. Now you've got me intrigued by the unbypassed 680R cathode on the driver. Since I'm only driving the tank with a single (un-paralled) triode, would that help me drive the tank better? Also, would 680R be correct for a single triode?

The Fender 135-watt PA amp and the 75-watt Lead amp both used single triodes for the reverb driver. In the 135 it had an unbypassed 820R; in the 75 it had an unbypassed 1K. BTW, the Acoustic 165 knockoff of the Mesa Boogie (the one that got them sued out of existence) used a 12AX7 with an unbypassed 1K8.
I think you can play around with it pretty liberally. I actually prefer the sound of the unbypassed Rk because it seems less "boingy."