20's neutrodyne valve radio

[Alan Douglas]

The capacitance would depend on the magnitude of the 180-degree-out-of-phase RF signal, where it's tapped off along the coil. For laughs I just measured a Fada "Neutrodon" from 1923; Fada was an early Hazeltine licensee. It measured from 1 to 6 pF as nearly as I can tell (subtracting the test-lead capacitance). It consists of a glass tube with two wires inserted, not quite touching, and a brass sleeve that slides outside but is not connected electrically.

[unrealdave]

Well I got this running yesterday, and it sounds OK.  Two things though.

It is a complicated thing to tune.  Once the Neutrodyne capacitors have been set correctly they are fine until you change the valves or the coils.  Once they are set though 3 stages of tuning means a lot of trial and error, although I guess once you have been through that stage a user would have experience and just know where to find stations.  We found 5 stations on mw that came in OK.

Getting the HT supply right was trial and error.  88v on the output valve and 44v on the 2 rf stages and the detector otherwise loads of howling and other awful noises.

I used two Mullard PM1HF’s for the HF stages, a Cossor 210HL for the detector and a Mullard PM1LF for the output stage.

All in all it sounds and looks great but I think Mrs Unreal thinks it is a bit big for the front room   .  It is impressive looking but takes up a lot of room and these things sometimes get broken up for the parts – they sell on ebay for £££’s but I think it will go nicely on a top shelf in the gym  

I tried to get a short video of it playing but my upgraded PC will not connect to my phone anymore.  I am looking at it  

[Crackle]

Excellent Dave. I think in the days when these radios were used tuning them was part of the mystique of using them.
I think some sets/people often used a chart listing the radio stations indicating the settings for each dial.

The image below is from a KB 156 Portable radio
Mike

[Alan Douglas]

Dials 2 and 3 should be very close.  There were jokes about three-handed owners, but some companies bragged about all their controls: The six-tube Federal 61 had sixteen knobs and dials and every one of them did something. Mohawk capitalized on the Scopes "monkey trial" that was a news media circus at that time:

       

[unrealdave]

I think in the days when these radios were used tuning them was part of the mystique of using them.

I agree - a bit like PC's in the mid 80's

[unrealdave]

Dials 2 and 3 should be very close.  There were jokes about three-handed owners, but some companies bragged about all their controls: The six-tube Federal 61 had sixteen knobs and dials and every one of them did something.  Mohawk capitalized on the Scopes "monkey trial" that was a news media circus at that time:

They are close
love the monkey