Fender High Power Twin (5f8a) grid stoppers

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Ondrej
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Fender High Power Twin (5f8a) grid stoppers

Post by Ondrej » Mon Feb 18, 2019 2:28 pm

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

Roe
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Re: Fender High Power Twin (5f8a) grid stoppers

Post by Roe » Sat Feb 23, 2019 3:19 pm

1k5 might remove some 100.000hz
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Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

Ondrej
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Re: Fender High Power Twin (5f8a) grid stoppers

Post by Ondrej » Wed Feb 27, 2019 5:26 am

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

Roe
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Re: Fender High Power Twin (5f8a) grid stoppers

Post by Roe » Wed Mar 13, 2019 4:33 am

sloppiness perhaps?
http://www.myspace.com/20bonesband" onclick="window.open(this.href);return false;
http://www.myspace.com/prostitutes" onclick="window.open(this.href);return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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