Re: Usage of Western Electric 350A?

On 30 May 2006 05:03:37 -0700, "izozaya" <izozaya@xxxxxxxx> wrote:

Hi!

I scored a dozen of WE 350A, but I am unsure as to what can really be
built with them.
First, I am unsure as to whether 350B specifications would apply to
350As, but also to what operating conditions would be more appropiate
for a good hifi amp. <snip>

350A: WECO-style 6L6 with 144A-type socket configuration and a plate
cap. Basically an early WECO 6146, designed as an RF tube, but almost
all characteristics are the same as the 350B (6L6), as follows:

"Normal" Operation Ratings:

Fil. V: 6.3
Fil. I: 1.6
Plate potential: 500V (350B was 450V)
Plate current: 85 milliamps
Screen potential: 250V
Power Output: 24 watts (350B max is 20)
Max plate dissap: 30 watts (350B max is 25)

Average Class A Operation:

Plate potential: 500V (350B was 450V)
Plate current: 55 milliamps (350B was 53)
µ: 430 (350B was 400)
Plate R: 67K (350B was 64K)
Gm: 6400 (350B was 6250)

Source: WECO General Bulletin, Vacuum Tubes, February, 1941

Does anyone know suggested operating conditions for this tube? <snip>

See above for all.

Have
there been commercial amps that have used this tube in the past? <snip>

The world's first negative feedback P-P amplifier, the WECO 101A of
1940, used 350Bs with octal sockets. What you have there is really a
bunch of early 6146s with WECO 144A sockets. Slightly greater µ and
Gm of the plate cap variety over the standard octal design would boost
performance just a tad. I owned two 101As with 350Bs...nice
amplifiers...not great, of course. They were good for about 14 watts
before clipping a fresh, matched pair. I sold them for $5000 for the
set, tubes extra.

You could build any 6L6 or 6146 amp with these tubes with excellent
results. A 6L6GC, however, will give you a bit more power. The
advantage of the WECO tubes is longevity. One of the 101A amps I got,
just out of service from the telco had a pair of 350Bs dated 1946 and
still tested good for Gm and cathode activity, and they'd been in
service continuously. Weak spot: output transformers were fragile on
those.

dB
.

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