As some of you may remember - -
I have stripped an old destroyed Gates
board that I found in a radio station
dumpster years ago. Most of it had
been reduced to unusable junk.
The old vacuum tube insides all
came out and will not be used
again.
There is a lot on line about
12AX7 preamps. I am considering
putting one in the board just for fun.
I see some of these circuits take a rather low
plate voltage - - down in the 30 to 50
volt range. Am I missing something?
It seems to me I would need 120 to
130 volts.
???
Brooce
If you Google "build a 12ax7 preamp" you'll get a craload of plans, kits, and info.
TIB
Back when the world began I built my first audio mixer board which served for many years as the heart of my recording studio which brought in the rent.
I think I had 6 input channels with the largest circular knobs money could by and the best pots... Duncan-Bradley I think.
The circuits where all mounted on cut-out aluminum from cookie sheets.
The audio booster amps were 12AX7s with circuits copied from a Gates Yard-Bird (if memory serves) at an FM station where I worked nights.
I can't remember what the mic pre-amps looked like, but they were probably also 12AX7s.
I never could figure out what was different about 12AU7s because they also worked.
Although they may have the same electrical connections, the power and gain figures are very different.
Here's a link to some info:.
Perhaps you mean....Allen-Bradley pots...??!
I worked at 2 stations that used the Gates Yard boards....both 8-channel mono (AM stations, LONG before C-QUAM!!!)......the external power supply for this unit was installed under the control room "desk"/console --- and was a real dust trap!! (no one ever thought to take a vaccuum or dust pan and broom into that "black hole"!!!!). BUT -- the boards chugged on for many years, until (finally!!) replaced with Solid Statesman units....
Ya, I think the board I copied 12AX7 circuits fromk was a Solid Statesman.
In another project a machinist re-tooled the capstan and head fittings of a Wollensak tape recorder so it would run at 15 IPS, and I replaced part of the recording circuit with a 12AX7 circuit copied from an Ampex tape recorder.
It was sort of a dumb machine because it only held 7" reels and had a 1/2 track head.
Running a spool of tape at 15 IPS took 15-minutes.
I will probably have more things
to post here as this goes along.
One way or the other - a 12AX7
preamp is going into this old
Gates Studioette.
Brooce