[John L Stewart]

Originally Posted by patrick-turner

On 12 Nov, 10:16, John L Stewart
wrote:
Here is a version posted by Yves Monmagnon & his collaberators Tomcik &
Wiggins to RAT on Sep 1/ 2004.

Hey Patrick, it looks like Yves has you beat by a few years. Such is
life.

Think of Darwin & Alfred Wallace on evolution. Few people remember
Wallace. Or what about Edison & the Brit Swan & the incandescent light?
Swan is now mostly forgotten except for their joint company Ediswan in
the UK. And development of the first jet engine(s), independantly in the
UK & Germany, only a few moths apart.

Cheers to all, John

I am lucky to invent things a few moths apart from other dudes. One
mustn't let moths into one's mind lest the intellectual larvae eat
holes in one's thorts and you end up with many holes in ideas, and
empty sockets on amps you try to build, and not knowing why :-)

But yeah, Yves beat me alright. I wonder who beat him maybe 40 years
ago, but only to also be ignored by everyone, and forgotten so much
more quickly due to an absense of searchable Internet stuff?

But Yves is using a 6V6 only, and has an unbypassed screen, with its
Eg2 supplied through 15k and adjustable pot. That just doesn't look
right. If g2 is bypassed to cathode, circuit becomes pure beam tetrode
with CFB, and isn't too bad, except for tetrode spectra that still is
there, but merely reduced by the NFB. Better, IMHO, is to have a shunt
regged and fixed Eg2 at about 3/4 the anode B+. Then the supply R to
g2 don't load the anode circuit, and NFB is applied to g2 circuit
because the 6V6 works as 20% UL in terms of its open loop gain.
Trouble is that hardly any OPTs with a 20% UL tap are ever made. But
quite a few are supplied with 40% tap. To then avoid having huge grid
drive voltages = say 50% of the Vak, the load value is kept a bit on
the lowish side, so that PO is high for the equation PO = Va-k
squared / RLa. Say you have 2 x EL34. Loads are Typically 3k6 per
tube, so for 2 parallel tubes the RLa = 1k8, and for the 18 Watts
easily available you have Va-k = 180Vrms, so that 40% tap gives Vk-0V
= 72V, and Vg-0V = 90Vrmsd, not too hard to do with an 6EH7 with about
10mA and CCS in triode and with gain = 45, so Vin without NFB = 2Vrms.
Rout with 40% CFB is low enough to not use GNFB, but that's also easy
to do if needed if driver = EL84 and a secind paralleled 6CG7 input
tube is used with normal type GNFB, and only 9dB max NFB is needed to
make sensitivty about a volt.

I guess if I tried to get to the moon before 1969, the yanks wooda
spent yet more dough and beat me and the Ruskies!

Patrick Turner.

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--
John L Stewart

It seems Yves was a busy guy back there 8 years ago. Here is another of his thoughts. The 4CX250 needs forced air cooling so having the plate at ground would help.

But lots of other problems!

Cheers, John