Looking for a tube only radio or radio kit

It depends on the biasing of the tube. Capacitive coupling, together with a largish resistor to goround (grid leak) create a grid-leak detector, and its gain can be improved with positive feedback.

The grid-cathode diode is the primary detection element, and the incoming AM modulation can be retrieved from plate current (or voltage, if there is a suitable plate feed resistor).

Detection is achieved by a little nonlinearity in the stage.

NT

On Friday, June 17, 2016 at 7:39:17 AM UTC-7, Phil Hobbs wrote: ...

It depends upon which frequency you expect as output from the stage.

If you extract the output at the RF frequency, yes it is a Q multiplier.

If you extract the audio that results from non-linearity in the active device then it is a regenerative detector.

That was an extremely common arrangement until superhets became common.

kevin

Using a Q-multiplier as a detector sounds pretty far fetched to me. Any published examples? (I don't regard myself as an expert on early radio, but I've studied it because there are a lot of similarities with modern optics.)

Cheers

Phil Hobbs

It was the most common radio configuration during the 1930s.

NT

Get any tube-era ARRL Handbook (the older ones are called The Radio Amateur's Handbook). There is a long explanation on grid-leak detectors with and without feedback.

My first ham receiver was an old one built around 1947, a superhet with a fed-back grid-leak detector after the first and only IF transformer. For AM, the detector was run just below oscillation point, and for CW (Morse with just on-off carrier), it was run oscillating and providing the necessary beat frequency to hear the signals.

Any kits available these days will probably be expensive.

There's plenty of simple circuits online and tubes can be salvaged from gear that turns up at flea markets.

I tried finding one that used transistors and no all-in-one radio chip, and turned up nothing.

Ebay has some AM transistor radio kits, i.e., unbuilt

as well as a variety of tube radios (AM, AM-FM. & AM-FM-SW), all built

and some AM tube kits

one of which - a 7 tube AM radio - for $9 features:

two in the discharge standard circuit; Modulated at 465KHz Plastic shell for the new material, and never go back to feeding. Each test port circuit Ic levels. Schematics, assembly drawings, and the other parts list, technical documents are complete.

Despite the description, it uses transistors, not tubes.

Probably something lost in the translation. Just as in England instead of tubes they would be called valves.

Could be the instructions are also in Chineese.

I doubt you'd find a tube radio kit anywhere, too unpopular and too much worry about liability for anything over 50v. And of course reaction adjusted by the user is a no-no now.

NT

Try here:

kevin

Parts list and notes on the schematic are in Chinese (though parts within the schematic are Roman, C1, R5, etc. Transistors are labeled V1, V2, etc.)

Since the plastic case never needs feeding there is some slight likelihood of a translation problem.

You got a laugh out of me.

I noticed that, but that's good. It means I can go out of town without worrying who is feeding my case.

It also says Power: 3V (5 batteries)

That seems interesting.