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…