On Tuesday, 27 August 2019 17:56:14 UTC+1, wrote:
After you have handled or been around in the mid-five-figures worth of vintage radios, you will learn not to reason from the specific to the general..
Magic words here a
1920s
Home Brew
Single tube
One can't always rule out an amateur builder working to their own outdated technical knowledge. But they clearly know enough to get a radio working, and it's not much more leap to bring the tech up to date.
a) Suspend all other expectations, and deal with what is in front of you.
O1A tubes come in several shapes, from globe to ST. I have seen one (1) "G" type as well, so anything is possible. There are also several other candidates that would do, including an OO, 30 and 112 amongst others. Some would require a different filament voltage. But, the O1A is/was the go-to as they were very common, and much cheaper than the alternatives.
useful to know.
b) Variable capacitors are/were expensive relative to fixed caps. So, your home-brew hobbyist likely picked a fixed cap at some value between that specified for a variable cap.
The one fixed cap on the ae input is in series with a variable cap! I suspect the variable was added later. The other controls are nice & symmetrical then then ae input VC is stuck round the side.
c) Fixed caps are/were expensive relative to nothing - so your home-brew hobbyist 'went without'. He/She (a great many of the earliest hobbyist were girls/women - why? Most of the parts were made by women). He/She was probably listening to a nearby "torch" station with little or no competition, so targeting to a specific frequency would be typical.
My homemade '24 set has lots of caps. But this one is, as you rightly conclude, a total cheapie job. The cabinet is nice but open the lid & it's clearly ill fitted pieces untidily glued together. The rest is similar.
Caps however were almost free. Take some paper & a little foil, tie with cotton & wax it and minutes later you have a cap. Any electronics book of the day explains this. A different history piece I have includes an HV cap made with plywood as the dielectric. I've never seen any graphs on how they perform
I guess it's still cellulose.
d) At the time, coils were either wound by the hobbyist or purchased to a specific range. If no plug exists, then your hobbyist was uninterested in, or could not afford that option.
e) At the time, there was no 'set standard' for radio parts, connections, hardware nor much of anything else. The typical hobbyist, working on-the-cheap as this one clearly was, would use what was lying around. Which might explain some oddball stuff.
It has 3 knobs, all clearly of the era but all different. I don't know for sure it was that way originally but it would not surprise me.
f) Note that the standard for *cheap* wire at the time was rubber/gutta-percha insulation. Which would crumble to dust in short order. So, PVC is no surprise.
I thought bare wire was the usual thing to wire up radio internals then.
"Waldo Semon and the B.F. Goodrich Company developed a method in 1926 to plasticize PVC by blending it with various additives. The result was a more flexible and more easily processed material that soon achieved widespread commercial use. "
So it could even be original wiring, though that's not likely.
On that one-handed coil - are there any taps on it? Commonly, a poor-man's SW or Airplane frequency coil would be done that way - one end fixed, and then tapped to the standard antenna for the alternate.
no taps. Looks like it was hand wound round a convenient round object, some sellotape added to keep it together & that was it. It has its own custom mounting made from the same material as the cabinet, so probably was fitted from the start.
Summing up, you have the equivalent of a fox-hole radio created with as few expensive parts as possible, following the general idea of the Armstrong circuit, which was 'all the rage' at that time.
Peter Wieck
Melrose Park, PA
Well, it's a fair bit better than a foxhole set but yes it definitely incorporates some 'whatever' parts, and some not.
NT