Last week I came across a Home Brew radio that I have drawn up the circuit for. Does this look correct and have a chance of working? There were a couple of solid wires loose but because of length I think I was able to correctly locate and terminate them. I am not sure of the voltages as it looks like there have been a couple of variations done. ie - lots of holes, and the terminal caps for the connections could have been moved. The tuner is I believe a Variometer with another coil fed straight from the antenna attached to it. I have attached a picture in hopes someone can verify what it is. I have been looking thru many old radio books and have not seen one like this. This set does have an open secondary on the second output transformer. I did try to hook up as if the second 201a tube and transformer was not there and got a slight squeal but the tuners don't seem to affect it.
To cut the babble short - does the schematic look like it would work? Do I have the voltages correct? Any words of wisdom?



edit... circuit diagram removed as it had an error in it. See later posting.

Thanks

Why is the antenna coil not coupled with anything? Are those air-core transformers RF transformers or are they supposed to be iron-core AF transformed?

Oops - they are iron core.

As for the coupling - just drew what is there.

It may look that way but it has to be coupled to something.

I suspect it's one of the greenish coils in the variometer, isn't it?

There is a smaller dia coil in the right of the picture above that can be adjusted to just slide inside the primary or it can be adjusted to be tilted outside of the primary. I did not know how to draw it up but it is the coil shown connected to the antenna.

That's what I suspected was the case.
I'm no expert on those early sets but my guess is that's the primary, the large concentric is the secondary (going to grid), and the rotating coil is the regen tickler feedback from the plate. Antenna coupling would be adjusted by moving that primary in and out on axis and regen by rotating the other.

The variable cap connections don't look right to me. Were one or more of the 'loose wires' coming from one or both of those?

Also the grid of the detector seems to be grounded.

That was one of the loose wires that given it's length would only reach the grid leak and that end of the grid leak was connected to anything I connected it there. Maybe wrong.

Just looked over the circuit again and it is not drawn correctly.

Making the corrections now.

Corrected the schematic. I was way off - I did have a bad cold when I drew it up .

Hope this makes sense.

As is it still looks like the antenna 'goes nowhere' so I'd suggest you redraw the input coils to reflect the coupling. I.E. The two concentric coils in parallel coupling, like your interstage transformers, and the rotating coil horizontal next to, or over, them.

Not sure I understand the directive... I am a newbee please reword.

The coil as drawn from the antenna to ground actually is linked to the Variometer but not physically attached. Is that what you are asking?

If by "not physically attached" you mean there's no core it doesn't matter. They're air coils and all three of those green coils are coupled, as in a 'transformer'.

Here is an example of the principle I think they were using in that radio.
http://makearadio.com/tube/1-30.php

See? The antenna coil couples to the secondary coil on the grid (which is a grid leak detector) and the rotating (feedback) coil controls how much regen takes place. I.E. coupling is maximal on axis so as you rotate it off axis the amount of regen is diminished.

That yours doesn't have a 'cylinder' they're wound on is completely irrelevant as it's there simply for convenience in winding and then holding the coils in place but any method is the same as they're air coupled, not through any 'physical' process.

And your audio tube filaments are wired in series- can't be right.

Scott Todd

The way it is wired. I will change that plus the switch only controls the the filaments of 2 of the 3 tubes. Will change that also.

IT SINGS!!!

I bypassed the open side of the second transformer with a .05 cap and a 4K resistor and got a clicking/humming sound thru the headphones. I could touch the variable caps and the sound would stop. I at least knew I was getting a signal thru from that point. While looking over some old schematics I noticed that I had not connected the antenna ground to the A+/B-. As soon as I did I could pull in a couple of stations. Upping the B+ 45 to 90 I could now drive a drum speaker. Whata rush. Thankyou to those that guided me.

If the audio stages work well as is why change the filament connections as that might require a higher wattage variable resistor given you will have twice the filament current with the filaments in parallel. I do agree with making the switch control all three filaments though.

I have not got around to changing the filament wiring and since it does play well I think I will leave as is.

I wonder if that was done for a reason other than saving on filament current?

With the quantity of holes drilled in the mounting board this radio has had many changes. I am looking to restore this set with new front and mounting board plus doing most of the wiring using brazing rod as it is locally available for not too much $. I will revisit the filament but will likely leave it alone. It works.