[Boatanchors] 'Ruggedized" 12AX7's ??

[sdaitch at kuw.ibb.gov]

Microphonics and TT preamps rang a bell.

Another source of microphonics, well, more
precisely, audio feedback, was between the
studio monitor speakers and the turntables.

Under some gain, levels and monitor volume
settings, we could have a low level oscillation
set up by any rumble in the TT system, amplified
by the monitor speaker system, then vibrating the
record disk and that could be picked up by the 
phono cartridge and back to the speakers.

It was mostly a problem if the studio monitors
were being fed off the modulation monitor, 
high volume levels for the monitors, low level
passages in disk material when the AGC equipment
between the control console and the transmitter 
pulled the audio levels up.  

Had not thought about that in many years.

73
Sheldon

----- Original Message -----
From: Alex Whitaker <ehscott at sbcglobal.net>
Date: Friday, December 31, 2010 1:23 am
Subject: Re: [Boatanchors] 'Ruggedized" 12AX7's ??

> I have heard from friends of mine who were in the broadcast 
> industry back when it was all tubes that 12AX7 tubes are a 
> perpetual source of trouble.  I guess that they kept a stash of 
> them in the control room for the turntable amps....the tubes would 
> get noisy and microphonic with use and frequently needed 
> replacement.  
> 73,
> 
> Alex 
> AA9XY
> >