Looking for a new or good used power on switch for an R-390A. Or perhaps someone can tell me where I can buy one from a vendor. Or maybe they are repairable? The R-390A that I have won't turn off.

Thanks, Ron

That is similar to one of my 200 ohm Shure mics which develops about 3.5 mVrms across a 1k load with a normal speaking voice at about 1" from the grill.

So your pre-amp has a voltage gain of at least 50 or 34 dbV.

Good deal.


Phil

"Don't let perfect be the enemy of good enough"

I think I'll hang that pic up in the shack!

Phil,
Sorry I misunderstood your question.  The RE27 spec quotes output per Pascal of sound pressure.  OK I guess if you know the sound pressure which I dont.  So I put the scope on it and measured 5 to 7 millivolts RMS in a normal voice with no load R.  Impedance is 150 ohms so it takes a bunch of gain to get to 500 mv.  This little pre-amp does it well with very low noise.

73s  Nigel

Para-sympathetic capacitance! 

is the bag of orange drops part of the circuit?

When you consider what stray inductances and capacitances can do, it amazes me all the more!

The measured impact of finger guards on fan noise!

This, and other fascinating application engineering information disclosures can be found here.

http://www.comairrotron.com/sites/default/files/files/COMAIR%20CATALOG.pdf

It’s called R & D! Love it

How to terrify a Klingon!