Newsgroups: alt.guitar.amps
Subject: Re: Stupid, stupid tube question....
Date: 20 Jun 1998 03:10:07 EDT
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Xref: geraldo.cc.utexas.edu alt.guitar.amps:110979
I heard it when I tested for it in the soundroom at GT, but only with a very
quiet power supply. Photons have energy, are energy, and when they strike
the plate, they impart noise. Normally that is buried in the sound floor or
too weak to even register. But when you have a tube way down at the start
of a high-gain circuit that is optimized for low noise, such as you have in
a tube amplified condenser mic system, photon noise can be a problem. It
depends on the sensitivity of the circuit and how quiet the rest of the
audio chain is. It's real enough that the Germans delt with it years ago in
the same manner as GT. That is also the reason the new GT mics do not have
holes in the case. A PMT (photo multiplier tube) is a vacuum tube optimized
to take advantage of this effect. You find these in use for optical
soundtracks on film and in some film to videotape transfer machines.
As the GT mics improved and we learned ways to lower the noise floor the
problem was revealed to us. We also got calls from mixers and producers who
ran into the problem. Consulting with audio pros helped to prove and
isolate the phenomena (too bad we didn't have some old Germans laying
around) (shut up, Roy) And the paint was a simple solution. Another simple
solution would have been to stop drilling holes and laser cutting logos into
the mic shells, but that was the visual ID of the product and, oh nooooo, we
could not mess with that.
Hifi guys who love to build tube preamps for MC cartridges also are aware of
this. I wish I could give you some references to look up, but I do not have
any off the top of my head and I'm too damn tired and stuffed up with the
latest cold to look. If you are still interested, I will make the effort
(to pick up the phone and ask someone, that is) to find some.
This is NOT a problem with guitar amps. We tolerate a noise floor level
that masks anything as low-level as photon noise. A monster 4 or 5
gain-stage preamp could reveal photon noise, but not with the noise floor
you usually get in a Mesa or whatever.
I have never seen sparks as a result of eating Wint-O-Green Lifesavers, and
do not know of it's effects with regard to vacuum tubes.
BTW, I said that damn tube was a Peavey when, of course it is Mesa. I knew
that. My brain caries the scars of the misadventures of youth.
--
To reply remove NOSPAM from address.
Lord Valve wrote in message <6mflf1$b3--(at)--jx-ixn2.ix.netcom.com>...
>In <6mf8ua$btk$--(at)--upernews.com> "profrets"
>>
>>I think that is the idea. It is shrink tubing, as far as I can tell.
>>When I was working for GT, it was discovered that light entering the
>>tube on the microphone products increased the distortion levels,
>>subsequently, they started dipping the tubes in heat resistant flat
>>black paint. This is a good case for tube shields,
>(snip)
>
>Lord Valve Speaketh:
>Man, that sounds like a load o' crap to me. I ain's sayin' it IS,
>but it sure *sounds* that way. Post details.
>
>Lord Valve
>Visit my website: http://www.freeyellow.com/members2/lord-valve/
>Good tube FAQ for newbies. Click the e-mail link and request a
>tube catalog. I specialize in top quality HAND-SELECTED NOS and
>current-production vacuum tubes. Good prices, fast service.
>
>"Ninety percent of everything is CRAP." - Sturgeon's Law (see above)
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