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In Reply to: RE: CCS set up for 1620 or 6SJ7 posted by GSH on February 22, 2015 at 08:31:05
"Here is the schematic of a driver stage using a 6BQ5 Pentode and CCS combo. Highlights of the circuit performance are gain of 125, output impedance of 500 ohms and distortion of .25% at 90 volts RMS. Not many driver stages can do .25% at 90V RMS! The operating parameters and measurements are on the schematic.
The performance speaks for itself. I guess I could just use a 6BQ5, but
I was hoping to adapt this approach to a 6SJ7 or 1620.
Follow Ups:
Ah hah! It's not "simple" CCS loading, which is known to be problematic.
If you want to adapt Gary's approach to a small signal pentode, consider the 6AC7. The EF86 and 6SJ7 run at low plate currents, which might be difficult to get right.
You said the mono tuner has an O/P of 0.1 V. There are pretty darned simple ways of getting the 20X or so gain needed. Gary's CCS setup, with a μ follwer O/P, loading a 6J5 is but 1 possible way.
Are you interested in trying Mr. Pimm's scheme, for its own sake?
Eli D.
Well yes, I am interested to try Pimm's pentode CCS technique, just to try something new. I wouldn't normally need so much gain.
I have used Gary's self-bias boards on 6J5, 7A4, 2C52 and triode C3o, with Very good results. But yes, these all have substantial current running through them.
So, perhaps a 6SJ7 is not a good choice with this idea.
I have a few 6BQ5's somewhere, seems like I should try that first.
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