On Tuesday, 27 August 2019 03:22:38 UTC+1, tabby wrote:

A little homemade 1920s 1 valve set with direct heated triode (unmarked). I've traced most of the circuit, looks very simple. Not tried to trace the main coil assembly with its 6 connections yet. The valve has a grid leak resistor for -ve bias without C battery. It runs high R phones, no speaker. 1st question is what sort of HT voltage and/or anode current should I aim for?


NT

From all the replies it seems I don't know much, other than to set it for an Ia of about 2-3mA. It's a 4 pin valve with a modern shaped envelope, so could be anything. I guess it's a dull emitter replacing the original bright.. There's no filament rheostat.

The circuit details are different to the Armstrong version here
https://en.wikipedia.org/wiki/Regenerative_circuit
-it's definitely a reaction set, no doubt there.

Apart from an input cap on the aerial there is NO other fixed cap anywhere in the circuit, so it's going to be horribly unstable, as if PFB on the edge weren't unstable enough already.

I reckon it owes more to 19 teen design than to late 20s, so I expect a very early 20s set. I expect the ae coupling cap, tuning & reaction will all interact some - not to metion headphone wire position affecting feedback as well. It's gonna be a fun one to use.

I presume the coil has a separate winding for the ae, and 2 more winds for the tank & pfb. PFB is controlled by a small varicap.

It got rewired at some point with pvc. Can't imagine why. The connections are all 2mm sockets, which seems anachronistic, but everything else is definitely original.

There's an extra hand wound coil that's only connected at one end. Can't see where it used to connect to. It connects to the ae input after the ae cap, and afaics the circuit ought to work fine without it in. Who knows.

The ae cap pretends to be something else, it's only marked as "the new and improved... stabilizer portable aerial... for better listen" and terminals are marked A & B. Will do some component testing later.


NT