Posted by PakProtector [ 205.188.117.72 ] on January 16, 2006 at 15:48:34:

In Reply to: Re: In the proper Tube tradition... posted by Damir on January 16, 2006 at 15:01:08:

hey-Hey!!!,
I think the pentode can do a better job in the Galahad amp. This keeps the stage count low, and input impedance high( even at HF, unlike Miller-assisted triodes ).

I discussed a g2 driven triode amp a while ago. Connect g1 to the cathode, and drive g2. Seems that high gm, low mu g1-g2 valves are the best for this. Things like horizontal output valves. There are some *REALLY* beefy examples of this family. The result is high delta-plate current for minimum input signal. Since making the discovery that the E-Linear 2-stage likes this sort of thing, I feel the need to explore further.

In the pentode circuit, the common cathode is ref'd to the common g2 node. With an increasing g1 signal, the cathode node moves towards g2 by half the signal magnitude. The other phase, with a grounded grid sees its g2-cathode voltage try to increase while it is trying to decrease its plate current. The capacitor here keeps the two valves behaving like pentodes by keeping this cathode-g2 constant. Picking a valve that is most sensitive to this action might be just the thing...and maybe it won't.

I wonder how a twin anode pentode like the 829 would work here.....
cheers,
Douglas

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