Metropoulos Forum

Hi,

while looking for schematics for my High power twin build, I found two versions: 5f8 and 5f8a. They mainly differ in the grid stoppers (5f8 has 1k5 for each of the 4 6L6's, while 5f8a only uses 1k5's for one of the pairs, while the other pair is left w/o any resistor), and screen resistors (5f8 has 100R, while 5f8a has 470R).

5f8 schem:
http://ampwares.com/schematics/twin_5f8.pdf

5f8a schem:
http://ampwares.com/schematics/twin_5f8a.pdf

Apparently most Fenders from that era do not use grid stoppers (e.g. Bassman). I would like to add the grid stoppers to improve the stability of the circuit.

Bassman schem:
http://ampwares.com/schematics/bassman_5f6.pdf

The question is: do you guys have any personal experience with these amps oscillating? Would the 1k5 have major impact on the sound?

Thanks

1k5 might remove some 100.000hz

Yeah, the question is, why has fender used grid stoppers for only one of the pairs... Cost?

sloppiness perhaps?

My 5F8A copy had uncontrollable feedback at any volume setting over 9 with the 1K5 on each pair. I installed 5K6 on each tube sounds great now.