I should have said the pentode has a high ra so the stage output Z is dominated by the load R. Unlike the triode, I suspect the overall output Z won't drift about with age as much as the triode would where the anode load is only slightly higher than ra, typically twice. I use 4k7 as my anode R. Great thing with the pentode is within reason, you can have any anode RIslandPink wrote: ↑Sat Jun 17, 2017 12:12 pm Yes I didn't spend any time measuring my phono, just measured parts and as you say, things like D3a's are tight tolerance. When I looked at values for pentode-driven first stage I remember that 3k or 4k anode load looked very feasible - so the output impedance wouldn't be that high . I think the D3a triode at 13ma as I have now, is over 2k Zout. Pentode did look good . Will be using something like that with the new LCR phono ( currently a top-plate and a big of bits ) although now the Gm amp idea from JC has come along and this opens up the possibility of a SUT-less MC input at the front end.
JCs ideas as always blow my mind. If you can get them stable, I'm sure it would be great. I just don't understand them too well, if at all.
And there's also shunt EQ that a pentode can do as well - no series R. Food for thought?
One day I hope to do an LCR (finances permitting) and I suspect that's the end of the road.
cheers,
Stephen