DIY Remote Broadcast Mic Preamp c. 1950

Download a four-page piece from RADIO ELECTRONICS, March 1950, on the subject of Build Your Own Two-Channel Remote Amp.  Author is Richard Finkbeiner.

DOWNLOAD: RemotePreAmp1950

Again with those T-pads.  Anyhow, we have here two 6J7 pentode stages in series supplying a 6F6 (v v similar to a 6V6) output stage.  Here’s the schematic:

The schematic is a bit opaque due to the fact that this piece is designed, ‘at the touch of switch,’ to become a cue amp – to receive signal, via its Station-Link, rather than send signal.  Confused?  The article will make it clear.  Anyhow, if anyone has tons of time on their hands, it might be interesting to re-draw this schematic minus all of that circuitry.  I would be v curious to know exactly which output transformer the designer used: a 5K to 600 ohm transformer that can handle 3 watts of DC and remains flat 30hz – 15khz?  Sign me up.  (It sure looks like a Langevin, but as I don’t have the early 50s Langevin catalogs, I can’t say which model it might be)  I can tell you that even the modern Lundahl that I use in my BRDCTR can’t offer quite that level of performance, although Lundahl does promise it…

Also of note to all you builders out there:  the author observed a full 15 db less overall noise with a 1620 in the input position relative to a 6J7 in same.  I wonder for how much longer we’ll be able to easily buy NOS 1620s…


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