tubes age 202
the power high for a 390? If you don't have a wattmeter, measure the B+
voltages. Maybe the regulator failed high. IIRC, there are at least 25 tubes in a
390. What tube functions were OK? Just the facts, sir.
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Date: Thu, 21 Jun 2007 11:41:00 -0400
Subject: Re: [R-390] maintenance
My experience with much simpler (fewer tubes, less "excess gain") radio is that
I often get the radio with the original factory (e.g. Hallicrafters-branded tubes in
a Hallicrafters or Daystrom-branded tubes in a Heathkit) tubes. The radio
works fine with the tubes. I pull the tubes and run them through the
transconductance tester and every single tube is below the acceptable number,
often two or three times low. I put new tubes in and the radio works fine too.
Maybe the AGC action is a little different with the new tubes. Now a 390 or 390A
has so so many gain stages (if not labeled gain then the mixers still provide
gain). There is no shortage of raw gain available from the tubes. Many of the
stages are operated with considerable degeneration and you will simply not
notice if the tube is considerably low in transcondunctance.
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Date: Thu, 21 Jun 2007 08:42:58 -0700 (PDT)
Subject: [R-390] re: maintenance
I think that you must be a victim of a *surge*. Vacuum tubes do not tolerate
overvoltage or mechanical trauma well. Operating them at design voltages in a
stable environment is the best way for a reasonably long life of 10,000 hours
(1.14 years if left on 24 hours a day). Adding a cooling fan in hot environments
is a very good suggestion. Bill Kleronomos wrote a real good article in ER in
1994 (vol 66 page 10) entitled *Electron Tube Survival Primer*. Perkins Electro
Acoustic Research lab in Canada ran some tests in which they found that
running a 6AK5W at an envelope temperature of 100_C resulted in a 50% tube
survival at 5000 hours, but 80% failed by 2000 hours if run at 253_C.
In the same article, they found running heaters at 5.04VAC gave the longest life
(albeit at lower emmisions); running at 6.30VAC had a 85% 5000 hour survival,
but running them at 7.56VAC led to a 20% 5000 hour survival. Hope this helps.
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Date: Thu, 21 Jun 2007 12:19:01 -0400
Subject: RE: [R-390] re: maintenance
I live in Florida and have a R-390 with a Johnson Invader 200 and a
HB4CX1500A amplifier. I don't leave any of them on any longer than absolutely
(14 pages)
(10 pages)
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