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In Reply to: RE: phasing issue posted by Tre' on June 30, 2017 at 09:16:29
That's what my question was from the start, do I use 67mA or 33.5 mA per tube. Now that I know the answer I will adjust the value of the cathode resistor to give me about 30 mA per tube so I am not on the ragged edge. Thanks.
Edits: 07/03/17Follow Ups:
That sounds about right.320vdc times 30ma is 9.6 watts
The 6bq5 will dissipate 14 watts (12 for the plate and 2 for the screen grid)
You could go a little higher safely.
320vdc times 35ma is 11.2 watts and that would be 80% of max dissipation (still in the "safe zone").
BTW with 8.8 volts at the top of the 130 ohm cathode resistor each tube IS running at 33.5 ma but that just shows that something is wrong.With only a 130 ohm cathode resistor those tubes should be running 80ma each.
I think your tubes must be worn out or the plate voltage is not what you said it is or something else is not what you say it is.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/03/17
I have to go back and start at the B+ and work forward from there. I want to try the unit staying within the recommended limits in the tube amp, so I want to try 250 vdc on the plates. I will report back with some new numbers when I think I have everything right and see what you think then.
The GE data sheet shows 250vdc plate, 34ma., 270 ohm cathode resistor with a 3.5k plate load for single ended triode connected Class A.So for PP triode connected Class A that would be 250vdc plate, 34ma per tube, 135 ohm common cathode resistor with a 7k plate to plate OPT.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/03/17
Thanks. I will start there.
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