Mic Kaczmarczik's TubeInformation - The Blue Guitar

From detritus@ix.netcom.com Thu Sep 21 10:15:02 CDT 2000
Article: 276885 of alt.guitar.amps
Path: geraldo.cc.utexas.edu!newsfeed.cs.utexas.edu!cpk-newshub1.bbnplanet.com!news.gtei.net!newsfeed.skycache.com!Cidera!cyclone2.usenetserver.com!newsout.usenetserver.com!newsfeed2.earthlink.net!newsfeed.earthlink.net!news.mindspring.net!firehose.mindspring.com!not-for-mail
From: Lord Valve
Newsgroups: alt.guitar.amps
Subject: SOVTEK TEST REPORT
Date: Thu, 21 Sep 2000 01:41:49 -0600
Organization: MindSpring Enterprises
Lines: 140
Message-ID:
NNTP-Posting-Host: c7.ae.e9.a4
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Server-Date: 21 Sep 2000 07:37:07 GMT
X-Mailer: Mozilla 4.04 [en] (Win95; U)
Xref: geraldo.cc.utexas.edu alt.guitar.amps:276885
Lord Valve Speaketh:
Just got samples of two new tubes from Sovtek...
the 12AT7EH and the 5751. Both of them look
just like the 12AX7LPS/EH inside and out, so
obviously the plates are made with the same
tooling and the bottles are the same. I only
got two of the 12AT7EH and four of the 5751s.
I did preliminary testing on them with my Hickok
752, and came up with some curious numbers; as
a control, I pulled two each of the NOS JAN 12AT7WC
by Philips and GE (at random from my untested stock)
and four NOS JAN 5751 by Philips. It seems that
the transconductance ranges on the Sovteks don't
match up all that well with the original American
tubes. Here are the numbers for the 5751s, in
umohs, per section:
SOV #1 - 1840/1900
SOV #2 - 2020/1880
SOV #3 - 1800/1860
SOV #4 - 1920/1840
NOS #1 - 1500/1460
NOS #2 - 1400/1420
NOS #3 - 1280/1280
NOS #4 - 1380/1340
It would seem that the Sovteks have higher
transconductance numbers than the NOS parts...
and that the NOS tubes are more tightly matched
>from section to section. (Close section matching
is a specification for this particular tube.) In fact,
the lowest TC measurement for the Sovteks is higher
than the highest TC figure for the NOS by a considerable
margin. Of course, this doesn't matter; you just need
to bear in mind that the Sovteks will have more gain
than the NOS will. I tried all of the Sovteks out in
my test rig...two of 'em had noisy sections. (One
case of Niagara Falls Disease, and one Harley Davidson
Infestation.) The two good ones were fairly free from
microphonics, and very quiet. Many of you who have
used NOS 5751s have found out that they tend to hum
in some circuits, especially high-gain front ends;
the Sovteks were remarkably free of this. Since
they're "hotter" than "real" 5751s, they will produce
more gain than the NOS; depending on what you're
looking for, this may or may not be a good thing.
When I get a few in the field, I'll have more to
say on the subject. So far, the reject rate (50%!!)
is not encouraging. Of course, the sample was very