Marshall 2061 Build - Screen Resistors?

[GregS]

The schematic I'm working from is accurate to the original Marshall 2061 circuit that was made from the late sixties to early seventies. There are no screen resistors in the schematic for the EL84 power tubes. From the research I've done, it seems a modern EL84 needs a screen resistor of at least 2K to prevent the screen from burning up. I also read that amps of the past typically used low value screen resistors or none at all. The way the tubes were made back then this was possible.

All this made sense and I was about to order screen resistors until I looked at a closeup picture of the inards of a new Marshall re-issue 2061 - no screen resistors!
Now I'm totally confused. Could it be that the screen supply voltage is not high enough to need them?

I'd rather not make changes to the circuit if I don't have to as I want this to sound as accurate to the original as possible. However, I also need this amp to be reliable and have reasonable tube life. I sure don't want to fry the Mercury Magnetics OT in the case of a tube meltdown and short as it's quite expensive. Perhaps some sort of compromise screen resistor value is the best way to go?

Any help with this would be greatly appreciated.

Thanks,

Greg

[GregS]

The schematic I'm working from is accurate to the original Marshall 2061 circuit that was made from the late sixties to early seventies.

I believe I'm mistaken about this. The schematic I have is from the re-issue model made only a few years ago. I guess screen resistors are not needed with this design.

Greg

[mooreamps]

I think the use of screen resistors is a new trick for guitar amplifiers, as I have read in the TUT series published by London Power. I personally use a value of 2.7 K 3 watt in my EL-84 based power amplifiers.


-g

[GregS]

I personally use a value of 2.7 K 3 watt in my EL-84 based power amplifiers.

Do you find using this value affects the sound much compared with a low value or no screen resistors at all?

I want to use screen resistors so that the amp is easier on tubes but want to retain the sound/character of the amp as much as possible. Would a lower value like 470R or 1K be a good compromise? - offer at least some protection for the screens without changing the sound too much?

I have a number of 5W resistors from 470R to 2.7K I can try out.

Greg