The Amp Garage

Update: Well got a new tranny in it and it sounds great. Voltages are good now tubes and screens are happy. Had one custom made at Pacific Audio Magnetics. Basically it a stand up version of their 100watt plexi replacement.
Thanks to all that gave input and suggestions.
On to the next build.

Not at the amp right now but I beleive it was 394v. I'll check the ohms tomorrow.

Sorry Martin guess I read your response wrong. Spec's sheet states 120v on primary places 350v on secondary loaded. lt places 388v on secondary under load. Of course when applying my full wall line voltage 125.5v when test was conducted that sent the secondary higher. To get the secondary down to 35...

By using a variac and monitoring voltages.

Update:

Ok the Hammond transformer was not at spec. So order a new tranny. I have used Hammond for years and never had an issue. Guess there quality control is going to crap to.

well before the tubes warm good the voltage is around 516v then as the tubes warm it falls. Now that i have it bias at 70% it settles around 494v but this is putting to much on my screens. Screens settle to around 486v. Now that i found the data sheet on the tubes max volts on screens it 425v. Any w...

no i was not running a variac. but measure voltage ac secondary 191.4 each. wall line 125v. Maybe I should and see how the voltage lines up.

Ok that was my fault I did not explain that well. My meter is a Bench top Keithley it is AC powered. I'm studying lord valve pages and other sources to try to under stand this and find a solution.

Not bad battery bad math. Meter is ac and calibrated a month ago.
2.98 /2,200 = 0.0013mA

490*0.0013 = 0.637mW screen dissipation.

Yell it seems off.

Ok added 2.2k screen resistors
plates 496v
screens 490v
screen resistors volt drop 2.98v
g2 and k is 490v
so if i calculated right screen current 4mA and screen dissipation 1.96 watts.
monitor screen voltage hit a hard A chord screens sag to 347v the preamp is heavy modded and very hot.

Wow Place in new tubes and screen voltage drop another volt Plates at 491 and screens at 489. Was checking volts drop across screen resistor to get the info to start calculating dissipation and shorted a tube socket out. What luck, but all seem to survive, but the socket and ht fuse after checking t...

ok lets take a step back. What started this all was over voltage mains. Max voltage on g2 is 500v's before the pole transformer was fixed I think it was 540 on g2. Is it possible I burned the screens out on the tubes. just a thought.

Thats what I'm banging my head over. I also never seen just a couple of volts between the plate voltage and grid2 voltage. Thanks for the math example that cleared the formula up for me.

If its clicking in my head measured k and g2
g2 = 499v
g2 and k = 498
so if I found the right formula 1.14ma x 1 = 1.14mw or is that watts
oh my 5watt 56k resistors on the screen caps is getting warm not hot but warm. sure if the amp was playing they would be very hot.

Back to the build, Ok calculated screen dissipation at idle using formula P=V²/R
Voltage drop across the resistor is 1.143v
Screen resistor = 999 ohms
Comes out P= 0.0013 mw
Does this look right?