|[AMRadio] 6U8 Subststute?|
km1h at jeremy.mv.com
Sat Nov 10 20:13:40 EST 2007
Actually the AC mains before a standard was set varied from 110-125V
depending on location. At that particular house I had a pole pig right
outside and my line was 121V most of the time. I also had a CE 100V which
was loaded with 6U8A's and they lasted just fine. The 20A was used to drive
Before jumping to conclusions that a tube swap has to be made check the
coupling and bypass caps for leakage. Do the voltages agree? The 290V plate
spec is a bit high and could be dropped down to 240-250 with little or no
effect. Has the PS been changed to SS?
The 6MU8 has a bit more pentode section dissapation at the expense of more
filament current; but the 6EA8 has more in the triode and even a tad more in
the pentode than the 6U8A. IMO it is a better plug-n-play fit.
If line voltage is an issue then install a small 12V transformer in a
bucking configuration with the AC line. Ive built bucking transformers into
dual duplex metal outlets at all my boatanchor operating positions and work
benches. Takes up a lot less room than a Variac which can then be used for
other purposes such as powering up BA's for the first time.
Glad to hear someone is still flogging those old CE's. I was always partial
to phasing rigs and would love to find a 100V again.
----- Original Message -----
From: "Jim Candela" <jcandela at prodigy.net>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Saturday, November 10, 2007 5:59 PM
Subject: Re: [AMRadio] 6U8 Subststute?
> ----- Original Message ----
> From: jeremy-ca <km1h at jeremy.mv.com>
> If the 20A is running them too hot then I'd check out the circuit for
> something causing excessive current drain. I used a 20A decades ago and
> never had that problem.
> Reply by Jim WD5JKO:
> Carl decades ago the line voltage was closer to 110-115 vac whereas now it
> is closer to 125 vac. A stock 20a plugged into todays AC mains will
> literally "cook" the tubes. Sure a variac is the right choice here, but
> the poor 6u8A is still the weak link. The 6MU8 is just a beefier
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