|[AMRadio] 100TH and 250TH advice and or comment|
Brett.Gazdzinski at verizon.net
Tue Aug 25 18:26:18 EDT 2009
I have a modulator that uses four 100TH tubes, it has had the same tubes for
the last 25 years, they look clear, and work fine.
I have a bunch of spare 100 TH and TL's, all look ok last I looked...
I have noticed a bunch of white tubes in the 7 and 9 pin tube stashes, maybe
the seals fail, the pins rust, or something happens and the air gets in.
You have a lot of thermal cycling on tubes that get used, from cold to very
hot, to cold again, but tubes just sitting going bad?
----- Original Message -----
From: "rbethman" <rbethman at comcast.net>
To: "AM Radio List" <amradio at mailman.qth.net>
Sent: Tuesday, August 25, 2009 12:06 PM
Subject: [AMRadio] 100TH and 250TH advice and or comment
> I have noticed that the 100THs and 250THS that are in their original
> boxes, either not used at all, or maybe use for less than an hour to
> test them, seem to be doing fine.
> Their envelopes are crystal clear an can not see any sort of defect.
> Then the ones that are in one of the two BC-610s that has the hours on
> it, even though it last performed flawlessly, now appears to have gone
> gassy with some milky white inside the envelope.
> Is this perhaps due to over heating or maybe I should phrase this as the
> convection cooling of these radios since they do NOT have fans.
> Ideas? Comments?
> It has always been metered and watched with a scope for observing
> waveforms, and the wattmeter is the newer Model Bird with peak reading
> built-in. (However true they really are!)
> Bob - N0DGN
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