I've worked on a few of these. Yep, the 811's are the best way to go. I
don't suggest the 572's as nothing is to be gained in power or life.
As to the filament not illuminated, I suspect a bad solder joint either in
the tube base or at the socket. Or the pins on the socket are somewhat
loose, allowing the metal to heat, thus opening the circuit to that tube.
Inspect the pins on the tube for any heating or discoloration. Same for the
socket. If the pin on the socket is discolored, likely overheated which
took the temper out of the metal. Solution, replace the socket.
You might try to re-flow the solder in the pins of the tube if you suspect
any heating or observe discoloration.
73
Bob, K4TAX
----- Original Message -----
From: "Steve Berg" <wa9jml@frontier.com>
To: <tentec@contesting.com>
Sent: Thursday, October 17, 2013 6:47 PM
Subject: Re: [TenTec] Failure Modes for 811a tubes?
I bought a nice Centaur amplifier from a list member a few years ago, and
finally got around to putting it on the air. I took out the 572B tubes
that were installed in the amp, and put the original 811A tubes in there
so that I would be less likely to blow up by 600 watt autotuner. I have
since bought a new 238C tuner from Ten Tec.
It was working fine, until the net last Sunday. Suddenly, the output
power dropped. I noticed later that the heater in the center tube was
out. I cycled the power switch, and it came back on for a while, then
went dark again. I have two sets of 572B tubes for the amp, but I am
curious about this being a common problem with 811A tubes.
Any pointers?
Steve WA9JML
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