Eureka!?

[Shad]

This is for a36watter with a GZ34.

Voltages are taken at idle.
Cathode Voltage 10.88V
Plate Voltage 352V
Screen Voltage 349
I have 351V before the screen R, 350 after it, using a 130 Ohm screen R.
My Plate Current for one tube pair is 66.4mA

If I am doing the caculation correctly I am getting this:
(352-10.88*.0332) = 11.32W plate dissipation at idle.
AND
(349-10.88*.0038) = 1.28W screen dissipation at idle

Anything wrong with this equation? Thanks.

[Plexi]

If you screens ar running that hot..or there is only that much difference between the plate and screens,you have a problem. You might measure the 1.5k resistor make sure its 1.5k and not 1.5 ohm You should be dropping more voltage across the sections of the cap.

The EL84 screens..is a bit too much,and if you did get this to work,the tubes would really cook with the voltages you posted.

Richie

[Shad]

Hey. Sorry I am using the choke, not the 1K5 resistor across the cap. I am using 130 Ohm screen resistor shared per pair of tubes.
I have tried it with some other value shared resistors before the two screen resistors.

With that experiment I did get a much larger voltage difference, but again back to the equation thing, when I do swap values I get much less dissipation on the plate and much more than 2W on the screens dissipation. So right now I just want to be sure I can at least properly calculate the dissipation. Unless of course the screen voltage is more important than dissipation.
Sorry I know I said only one question, but isn't raising the screen resistor supposed to also change the dissipation for the better, not just the voltage?
So I don't doubt I may have other problems, but really need to be sure I have a grasp of this math equation, and it looks like either my math is still all wrong, or I am not grasping how the screen R affects things.

May I ask if you think a lower voltage, with higher dissipation is better for the screens than a higher voltage within proper disipation?
If I do have the dissipation math down could you look at the other values I have tried and let me know what you think I might try next.

I am prepared to try anything, I just want to be able to fully grasp what any changes I make are actually doing.

I am begining to suspect my choke. Should I try to remove it and replace with the 1K5 just to see what happens?
I know it doesn't really matter which is used but I did want to use the choke. I will ditch it if needed though. It was the only trafo that cam unlabled but I had thought that most any choke woudl do and so never suspected it as the wrong one or bad.

Many thanks for your time man, I am quite sure you could be doing a thousand other fun things besides helping me.

Any other math gurus want to give me a nod or nay on the math equation would be much appreciated.

[Shad]

Sweet!
Ok removed the choke, put in a 1K5 R across the cap and now my voltages are looking much better.

Cathode 10.10V
Plate 352V
Screen 323V

With my 130 Ohm screen R I have 3.8mA screen current per tube.

Plate current minus screen curent at 30mA

Plate dissipation at idle 10.49W
Screen dissipation at idle 1.18W

Should I be concerned about the plate voltage at this point?

I don't see that high a plate voltage listed on any of the voltage charts I have seen so far ,though I am sure I have read in posts about some folks having plate voltage this high.

Well, given that I have likely already cooked these tubes alot I am at least going to button it up and see what she is sounding like these days.
However I am curcious about opinions on the plate voltage. Should I think of upping my ctahode R's? I have 130's in there now.
Thanks again Richie you got me back on track.

[Moose]

Should I be concerned about the plate voltage at this point?

I don't see that high a plate voltage listed on any of the voltage charts I have seen so far ,though I am sure I have read in posts about some folks having plate voltage this high.

Don't worry about the plate voltage, as long as your dissipation is reasonable, a good set of tubes will handle it. EL84s are, theoretically, 300V tubes, but I've seen them run higher than 385V in reliable, commercially produced, fixed bias amps. And, I've got some amps out there running 350V+ cathode biased (including in an every-night touring band with a 36watter) without discernable problems.

Just keep an eye on the dissipation when you pop in a new set of tubes, just to be safe.

[Shad]

Thanks for all the help folks.
So I have found some new problems but I think I'll have them licked but tomorrow.
When I first charged up the caps I had an old telefunked recto that started humming around 50 volts and continued getting louder as I upped the voltage. This being my first amp I though "well maybe it does that because of ythe lowered voltage running through or the caps forming"...whatever, lesson leraned.
Bewteen the shoddy recto, and/or my choke/resistor mistake I have fried at least one cathode cap. So all new caps are in order, a fresh charge with the new GZ and some new tubes and we'll see what gives.
FWIW the only issue I seem to have left sonic wise is an oscilation that expresses itself as a doubled/mirrored note around the 2K area (and subsequent octaves higher or lower.
After swapping OT leads, twisting PI leads on pin 1 and 6, and all kinds of other jazz including increasing the tail of the PI as Aiken describes to try and fix crossover distortion resulting from blocking disortion.
This looked to work on my scope but in the real workd I would still have problems.
Oh and I could hear the tone of my signal generator rining inside the chassis!
Knock on wood I hope with fresh tubes, and caps, things will be right as they should be.
Anyway thanks for everyones help. Will report back after I get new goods on the board.