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RE: phasing issue

Posted by Tre' (P) on June 30, 2017 at 09:16:29

In Reply to: RE: phasing issue posted by vinnie2 on June 30, 2017 at 03:52:05:

No Vinnie, I'm not trying to tell you what to do.

I'm saying that if both cathodes are connected to the one common cathode resistor (BTW that is the right way to do it) and there is ONLY 8.8 volts at the cathodes then (according to the plate curves) there should be a lot more current flowing through the tubes.

Something is wrong or your tubes are worn out.

Please look at the triode plate curves that I posted a link to.

Look at 320 volts and 8.8 volts grid.....do you see where the current is?

"The tube manual says 67mA for the 6bq5"

That's Max current and not where you want to operate each tube.

Also, where the data sheet says 130 ohms cathode resistor for 2 tubes that's pentode connected. This is not what you are doing.

The data sheet shows a cathode resistor of 270 ohms for one tube at 250vdc plate.

That would be 135 ohms for 2 tubes but you plate voltage is higher so that's not what you want.

Again look at the triode curves. Everything you need to know is there.

The red dot is at about 8.8 volts bias and 320 volts plate and it's 80ma.

That would be for one tube but you have two tubes.

The way you have it now there should be 160ma of current total.

That's not what you want to do.

Again, the triode plate curves show that at 320 volts plate the bias should be at -15 volts to get about 33.5ma from each tube.

That should take a 223 ohms resistor to give the 15 volts bias and if it doesn't then something is wrong.

Tre'

Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 06/30/17

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