With all due respect to those more experienced than I, don't get too wrapped around the axel with accuracy on those 1 ohm resistors. If you are using a typical DVM to measure them, the resistance in your test leads will likely introduce more than 1% error into you measurements.
Just assume 1 ohm and...rock on!
And...if it's any consulation, I link up with a couple of old salt EE's from time to time (retired AF officer and defense contractor) who go back to the vacuum tube heyday and they always chuckle when I start discussing component and power tube biasing tolerences and such.
Their standard fallback comment to me is...."Dave..ya gotta understand that in the vacuum tube realm...+/- 10% don't mean shit!". Meaning that these systems are quite robust and have pretty wide operating range tolerences.
Personally, I start with a powertube bias that approximates 70% max dissipation with 1% cathode resistors and tweak it to taste from there. As long as there is no red plating...it's good to go.
I maintain an acquaintence's JCM 800 and he likes the tone at 90% of max dissipation. He plays out 2-3 times a week and is using the sampe power tubes (JJ's) that I installed 2 years ago.
Now...a quick favor to ask: Any chance that you could measure the voltage drop across R20 and R21 before you make any changes to the B+ string? I would like to know the screen current at your present conditions so I can do a reality check on how I am interpreting the tube performance curves. Set your DVM to ~20VDC and slap one lead on each side of the 1K resistor. Polarity doesn't matter much as we are looking for a differential voltage.
Obviously...use extreme caution here as you will be in close proximity to lethal voltages!!!
Sure wish that this thread started ~3 days earlier. I had just placed an order with Mouser for the final parts for my express build and would have gladly bulked it up for your stuff and saved a few quid in the shipping for you.
![Mad :x](./images/smilies/icon_mad.gif)
Cheers,
Dave O.