Re 572-B, 811-A

[Randy Kaeding]

The local FM station here uses two 4CX250B tubes as drivers for the
3CX15000A PA. We had a lot of problems with the transmitter suddenly going
off the air, and the status lights indicated a driver tube problem. As a
quick fix to get the transmitter back on the air, we just change the tubes.
One time the problem showed up while we didn't have any spare driver tubes,
so I tried some of the used ones still on the shelf. Through
experimentation, I found they all worked, even the ones that had failed
before.

I discovered that the Svetlana brand tubes exhibited the problem, while the
Eimac tubes didn't. As a last-ditch effort to find out what was going on, I
decided to check the tube pins with a micrometer. I found the pins on the
Svetlana tubes to be slightly smaller diameter than the Eimac tubes.

Anyway, just my personal experience with Svetlana tubes.

Randy, K8TMK

----- Original Message -----
From: Ron Bracklow <n6pww at EARTHLINK.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Wednesday, June 21, 2000 2:50 AM
Subject: Re: Re 572-B, 811-A


> If you use Cetron, Penta Labs, or Svetlana tubes, you won't have that
> problem.
>
> 73,
>
> Ron.
> ----- Original Message -----
> From: "Murray Leshner" <multi-volti at SOFTHOUSE.COM>
> To: <HEATH at LISTSERV.TEMPE.GOV>
> Sent: Tuesday, June 20, 2000 8:17 PM
> Subject: Re: Re 572-B, 811-A
>
>
> > Wasn't there a concern awhile back with the newer tube vendors on the US
> > market about whether the tubes are suited for horizontal operation
> > (otherwise grid could sag & short to cathode). I think it was a problem
> with
> > only one of these two tubes, and I'm sure the question has been answered
> > countless times since...I just never heard the history of the problem
> beyond
> > the initial discovery.
> >
> > Murray
> >
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