screen voltage compared to plate voltage

[arfy]

A friend’s Traynor Guitarmate Reverb measures almost 20 volts higher at idle on the screen of the EL84’s than on the plate. This one is the earliest version I think and the power supply has a 10 ohm resistor between the plate and screen supply instead of a choke. There are no screen resistors on the tube sockets.
Will this be a problem or should I leave it alone? I just did a cap job and put in NOS 6P14P-EV/7189A’s I got from Lord Valve, which are nice and stable at idle.
So, a bigger power supply resistor between the plate and screen supplies, screen resistors on the tubes or leaving it as is are the options.
What do you people think/recommend?

[jimipage]

from the RCA manual (RC-28, pp.99):

"When the screen-grid voltage is supplied through a series voltage-dropping resistor, the maximum screen-grid voltage rating may be exceeded, provided the maximum screen-grid dissipation rating is not exceeded at any signal condition, and the maximum screen-grid voltage rating is not exceeded at the maximum-signal condition. Provided these conditions are fulfilled, the screen-grid supply voltage may be as high as, but not above, the maximum plate voltage rating."


maybe this can help?

[CathodeBiased]

A friend’s Traynor Guitarmate Reverb measures almost 20 volts higher at idle on the screen of the EL84’s than on the plate. This one is the earliest version I think and the power supply has a 10 ohm resistor between the plate and screen supply instead of a choke. There are no screen resistors on the tube sockets.
Will this be a problem or should I leave it alone? I just did a cap job and put in NOS 6P14P-EV/7189A’s I got from Lord Valve, which are nice and stable at idle.
So, a bigger power supply resistor between the plate and screen supplies, screen resistors on the tubes or leaving it as is are the options.
What do you people think/recommend?

If I were you, I would replace the 10 Ohm with a 1K 2W (5W if it makes you feel better and will fit) in the power supply PI filter, and install 1K 2W screen resistors. I use this topology in my best sounding EL84-based design.

[Darkbluemurder]

A friend’s Traynor Guitarmate Reverb measures almost 20 volts higher at idle on the screen of the EL84’s than on the plate. This one is the earliest version I think and the power supply has a 10 ohm resistor between the plate and screen supply instead of a choke. There are no screen resistors on the tube sockets.
Will this be a problem or should I leave it alone? I just did a cap job and put in NOS 6P14P-EV/7189A’s I got from Lord Valve, which are nice and stable at idle.
So, a bigger power supply resistor between the plate and screen supplies, screen resistors on the tubes or leaving it as is are the options.
What do you people think/recommend?

If I were you, I would replace the 10 Ohm with a 1K 2W (5W if it makes you feel better and will fit) in the power supply PI filter, and install 1K 2W screen resistors. I use this topology in my best sounding EL84-based design.

Good suggestions. The 10 ohm is definitely low. Most chokes in that place have 150-200 ohms. You can also use a 330-470 ohm resistor in that position. I did that with my Guyatone clone to replace a (otherwise fully functional) choke with solder terminals (whatever hell tempted this manufacturer to use solder terminals with 500V on them outside the chassis - this is even worse than not using bleeder resistors in the power supply). 1k should work as well. I also advocate using 1k screen resistors (2-5W of any composition except carbon comp). Ideally the screen voltage should not be higher than the plate voltage although I don't know the technical reason for it.