From tremolu–(at)–ol.com Sat Apr 8 11:42:49 CDT 1995
Article: 46965 of rec.music.makers.guitar
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: rec.music.makers.guitar
Subject: Re: Help: Did I Get a Bad Set of Tubes?
Date: 8 Apr 1995 03:30:24 -0400
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YES!!! Call and bitch!! You’re right on the money. Send them back in
exchange for tubes that are matched. Be sure you call them and be polite
but firm. Clearly explain the situation, and tell them you want a MATCHED
set next time, and you’ll tolerate no more than a 4 ma current difference
between the two.
I’ve seen this recently from Antique as well. A buddy bought 4 NOS GE
6BQ5s. Three were well matched, but the fourth was 12 ma hotter than the
rest. He called and bitched, and they agreed to refund his matching fee,
as well as try to get him a new set.
Sometimes Antique does a good job, sometimes not. Also, one thing I’ve
noticed about those Sovtek 6CA7s (and New Sensor, the importer, is aware
of), is those tubes exhibit high screen grid intercept. You’ll notice
little peep holes in the side of the plate structure. Look inside there
when the tubes are running. See if you can spot any screen grid wires
glowing red hot from beam interception. These tubes have a known grid
alignment problem. Also, you gotta get that bias current UP!! Try 35 ma
per tube!!! 25 ma is borderline overbiased. Anyway, if you have
incandescent screen grid wires, watch out. Screen intercept will increase
when you start driving the tubes with signal, which means these wires will
get even hotter. If one melts and flips out due to spring tension, and
touches the beamformer, catastrophic amp failure is likely. It will be a
screen grid to ground short. Resistors will instantly smoke. Hope to
hell your fuse blows before your transformer does. Sadly, there are known
problems with the 6CA7, so I recommend avoiding them altogether until the
Russians fix it. If you really want a 6CA7, Angela has the NOS
Sylvanias, but he’ll want about $50 each.
Regards.
From tremolu–(at)–ol.com Thu Jun 1 00:00:03 CDT 1995
Article: 1488 of alt.guitar.amps
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: alt.guitar.amps
Subject: Re: Tube questions
Date: 31 May 1995 01:32:11 -0400
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Reply-To: tremolu–(at)–ol.com (Tremolux)
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Of course, the local Sovtek types won’t shoot themselves in the foot!
They won’t mention the screen grid problems unless specifically asked. I
talked to New Sensor about it, and they said that they knew all about that
problem.
Specifically, it appears that the winding of either (or both) the screen
or control grid is sloppy. As you know, the screen windings is supposed
to be in the electron shadow of the control grid so as to minimize
interception (the grid wires are aligned). They miss in some spots,
because if you look into the peep holes on the sides of the plates, you
can see a couple of individual screen wires glowing orange, at idle. With
drive, the current rises, which would heat these wire segments even more.
If one melts, and flips out due to spring tension and touches either the
beam former or plate, fireworks.
Regards
