[Analogdino]

On Tuesday, 2 October 2012 21:41:59 UTC-4, John L Stewart wrote:
Analogdino;963098 Wrote:

Quick update:

Tried a pair of good 5881's, bias optimized, even balanced the cathode

currents to around 1.5 mA.

No good!

Max p-p volts across 8 ohms = 40 VAC, 200 Hz.

Thus, power = 25 watts.

Pretty much same as 6L6's, not really surprised.

We soldier on...

Cheers,

Roger



An intriguing solution to the drive problem can be found in the 6U10

triple triode. Triodes 1 & 3 look like a 12AU7 while triode 2 is similar

to 1/2 of 12AX7. All that makes possible a drive cct as used in the

Mullard 5-10 & 5-20.



Input gain stage uses triode 2 while the LTP consists of triodes 1 & 3.

No need for another hole in the chassis, just enlarge the existing hole

to accomadate the duodecar socket.



A much better drive for the 6L6's or whatever.



Cheers, John
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John L Stewart

Interesting idea, John, but there's a lot of chassis space for an extra hole. Also, that would give a bit more wiring space (the 6AN8 is already "tight".} Anyway, now it's all back together with "borrowed" EL34's (from my Leak TL/25) I now get over 40 watts RMS, max, so I'll not be redoing the front end as planned, will just leave it "as-is" (but with a 470K screen dropper replacing the original 1.5 Mohm) - this slightly increases the 6AN8 plate current to, IIRC, just over 1 mA - better, IMHO.
BTW, I've got a line on a couple of new Russian EL34's (that I can afford!), so the Leak TL/25 will likely get them and the W7-M will have to live with the present weak ones! Loud enough for me, for now...
Cheers,
Roger