[R-390] Tubes glow blue

[Roy Morgan]

At 10:46 AM 9/19/2005, mikea wrote:
>Roy's otherwise-excellent post unaccountably omits mention of one
>particularly-to-be-avoided form of glow in tubes.

Oh, goodie..something of interest to hear about!  Thanks, Mike, for helping 
with this technical stuff.

>When a metal 6L6 starts glowing visibly, then you have a serious
>problem and need to investigate it *IMMEDIATELY*. That's especially
>true if it's glowing blue. I've never seen one get past glowing red,
>and then only for a fairly short time.

Ah yes. This reminds me of the article (was it in QST?) many years ago of a 
set of 6 or 8 6AG7's being run to a KILOWATT peak input in a linear by 
being inverted in oil and run with some 1000 volts on the plates.  I think 
they experienced "reduced tube life".

It also reminds me of the 6550's in a Western Electric audio amplifier I 
have here that ran (briefly!) with one pair of plates quite red.  I really 
must replace those old coupling caps and check the bias supply....


>... hadn't
>thought it would be fast enough to stimulate Cerenkov radiation, but
>it sure is the right color.

"Cerenkov radiation"? Hmmm.... www.dictionary.com says:
"light produced by charged particles (as electrons) traversing a 
transparent medium at a speed greater than that of light in the same medium 
called also Cerenkov light "

*I* think the electrons whamm the glass which un-glomms some blue photons 
it's been keeping.  Did you know you can buy 6550's with blue glass?  They 
sound much better, some say.  AES has 'em from JJ Electronics. Only $40 each.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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