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Old 30th August 2003, 01:33 PM   #11
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You probably missed the 6V6 PSE appropriately illustrated with a diode
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Old 30th August 2003, 05:52 PM   #12
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Default Re: On third thoughts....

Quote:
Originally posted by dhaen
The input transformer's secondary is at the 6V6 control grid voltage.
Actually, if the bias control is set at -150V and the output is at 0V, the two grid leak resistors divide the voltage to -100V.
You'll note that if the grid were at 0V, the plate would have to be pretty close to 0V as well.

I'd love to breadboard this thing but I don't have a 300VCT power supply, hmm....

Tim
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Old 30th August 2003, 08:35 PM   #13
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Well I have the power supply for it but the single gain stage hasn't sufficient gain for what I would need without the step up transformer which I don't have, plus I don't really have the time.

Thanks very much for the circuit though I might adapt it to my own use later.
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Old 30th August 2003, 09:22 PM   #14
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Maybe you should try say, 12AX7 or 6AU6 for gain, and a sufficiently big triode for the CF, just cap couple the stages so you can get enough signal going. (Neg. supply still needed for the CF of course - unless you use a choke load.....)
Bias to the output tube by varying bias either to CF or output tube grid (when using choke; note this uses a coupling cap between CF and grid ).

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Old 31st August 2003, 11:46 AM   #15
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Yes that is what I am doing using the 6em7. section II is the choke loaded (plus resistance to assist juggling the output potential) direct coupled cf driver for the 212 output stage. The grid of stage II is grounded via a 100k voltage pot which enables me to fine control the bias on the 212.

The circuit is nothing new or special, and it hasn't enough gain (single va stage and no step up transformer) to drive the 212 to the full 40 watts, but it can party at over 20 watts effortlessly.

As I said what I liked about your idea was the possibility to use a single power supply for that part of the circuit. I am using one power supply for section I and the +/- supply for section II. Also I must isolate the two sections, but for that I have some Russian Teflon caps so they shouldn't be too big a loss of quality. The important stage for direct coupling is the driver to power stage. That is as long as safe operating points for sturdy valves are chosen.
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