1967 Marshall Super PA KT66 screen voltage question

[Charlie Wilson]

Now I am confused. The Drake 1202-84 /4k primary impedance is the stock Marshall transformer for a quad of kt66. Same one that is in Hendrix's Monterey amp.
CW

[martin manning]

Yes, I edited after looking it up. It's really not a good place to be operating, but a little better at lower voltage. FWIW, Brian Wallace thinks either KT66 or EL34 will be fine with that transformer.

[Charlie Wilson]

Thanks Martin. Well the amp now has the Merren power transformer and the TAD KT66. I think I'll use the lower B+ 460v secondary taps.
CW

[Roe]

Hmmm, let me rephrase my original question. Will TAD KT66 take higher than the spec sheet 400v? As far as variacs and butchering vintage amps. This amp is to be sold and I feel better selling an amp to a buyer that can plug the amp into the wall than having to get a step up or variac and hope they know what they are doing. Obviously the original transformer is included with the amp and is easily put back in if they choose. Again, I repeat, NOS GEC KT66 are $1400+ if you can find them so that is not an option.
CW

yes 500v at the plates is no problem. how much screen resistance you need depends on the voltage really. many of these amps have been running for a long time with these new tubes with original 1k screen resistors and roughly 500v at idle (which will sag significantly under load)

[Roe]

Now I am confused. The Drake 1202-84 /4k primary impedance is the stock Marshall transformer for a quad of kt66. Same one that is in Hendrix's Monterey amp.
CW

yes, but el34s were introduced in february 1967 with the drake 1202-119 OT (1k75 Z)

[martin manning]

...el34s were introduced in february 1967 with the drake 1202-119 OT (1k75 Z)

1k7 is really too far the other way, and depends upon significant voltage sag to stay out of trouble.

[Roe]

...el34s were introduced in february 1967 with the drake 1202-119 OT (1k75 Z)

1k7 is really too far the other way, and depends upon significant voltage sag to stay out of trouble.

yes, this is pretty much the history of marshall 100w amps from 1967 until recently. redplating is all too common

[bepone]

3k4, 3k5, 3k6 is a standard for 2*EL34, half of that for quad

[Roe]

3k4, 3k5, 3k6 is a standard for 2*EL34, half of that for quad

yes, but in the case of marshall the problem is the 100w amps, not the 50w ones, due to voltage differences

[Reeltarded]

...el34s were introduced in february 1967 with the drake 1202-119 OT (1k75 Z)

1k7 is really too far the other way, and depends upon significant voltage sag to stay out of trouble.

As per my post '66 45 amps (JTM50) tube rectified or not and 34s with either OT configuration, 100s finally @1k7 like Roe says.

100w magic is 2k5 and 34s.Baaaaa WAAAAHHHHHRRR

[Reeltarded]

...el34s were introduced in february 1967 with the drake 1202-119 OT (1k75 Z)

1k7 is really too far the other way, and depends upon significant voltage sag to stay out of trouble.

yes, this is pretty much the history of marshall 100w amps from 1967 until recently. redplating is all too common

YES this.. poor screens..