[NostalgiaRadioTime]

I'm working on an Atwater Kent model 20C 7570 and am wondering what the plate voltage to ground should be for the UV (or UX) 200 & 201 tubes? I'm measuring 27 DC Voltage on the 200 and 94 - 97 DC Voltage on the 201 tubes. The 201's seem right where they should be, as I'm using an ARBE III Battery Eliminator and the B voltage is set for 90.

Here's a link to a PDF file of the schematic:
http://www.atwaterkent.info/TechData/Dra...570sch.pdf

I had to replace both audio interstage transformers with the P-T156's available from Antique Electronic Supply. If the secondary of the audio interstage transformer's polarity is reversed or in the opposite direction of the primary, is that critical?

And for the ARBE III Battery Eliminator if interested:
http://www.arbeiii.com/

Many thanks for any help you can provide.

[morzh]

What do you mean by measuring AC volts on plates?

[NostalgiaRadioTime]

Sorry meant DC voltage....

[gregb]

The detector plate voltage should be 22.5 volts but you are close enough it should work. Do you have that detector B+ lead connected to the 22.5 volt terminal on the ARBEIII? If so you should be go.

Gregb

[Mondial]

UV-200 tubes operate at low plate voltages, usually from 22 to about 45 volts. These tubes contain a low concentration of argon gas, and they must operate a low enough voltage that the gas does not ionize.

[NostalgiaRadioTime]

Thanks, Mondial. I was worried I wasn't getting enough voltage off of that tube (or too much, as they are hard to come by!)

Yes, GregB, I do have the detector B+ lead connected to the 22.5 volt terminal on the ARBEIII. I think I have to replace the .002 "phone condenser" yet with a .002 mfd and see if that makes a difference. But my gut feeling is it may be a reversed polarity on the secondary of the AIT. If anyone has any experience with those Antique Electronic Supply replacement AIT's, let me know.

[gregb]

What is the issue Greg? Is there no output? Do you have a signal tracer or a scope?

Gregb

[NostalgiaRadioTime]

There's hum, and the rheostats do change the output level, but I'm not receiving any semblance of a station. The 3 coils all check out fine, and none of the rotars or stators are touching on the tuning capacitors. I just came up from the basement shop tonight and will dig out the signal tracer tomorrow night and see if I can find anything with that. I was mainly concerned I may have the green secondary wires on the new AIT's reversed and that it could be causing problems.

[gregb]

Try touching the grid leak with a screw driver and see if you get the some buzz in the output, that will prove that side of the set.

Gregb

[NostalgiaRadioTime]

Well here's an update on what I found tonight. The audio output section is working fine, however I'm not getting a signal through the 2R section and back (RF section). When I touch the plate of the UX-201 tube in the 2R section I get no buzz only very faint change in static. The 3 coils all check out fine, both primary & secondary for continuity. The antenna connections check fine for continuity (but I get no change in sound when I touch the antenna connection lug with the set on). I'm thinking it has something to do with the tuning capacitors themselves. I know that the 1st tuning capacitor had 'fins' touching and I tried adjusting it a bit. More work tomorrow I guess. Funny how quickly 3 hours can pass when you're working in the basement on a radio

[Radioroslyn]

I believe the 20 has wire wound resistors in series with the tuning caps to prevent oscillation. Check to see if any are open.
Terry

[Ron Ramirez]

Bingo, Terry hit the nail on the head. The 20 does have wirewound resistors in series with the tuning caps, and they are probably all open.

If you haven't heard a properly restored three dialer in operation, you will be amazed at how well such a crude receiver can perform. Good luck - you will enjoy that 20 when you get it going.

[morzh]

Just out of curiosity....not doubting the open wirewounds but....why would those open unless the oxidation does it to them? Even a shorted tuning cap in this setup in grid circuits will not do anything bad to them.....is that it? oxidation?

[Ron Ramirez]

Probably. All I know is that I owned a 20C-7570 (Compact) several years ago, and all of those resistors were open. Once replaced, the set came to life and worked extremely well.

[morzh]

BTW it's a neat solution (I never dealt with battery tube radios so far) to only switch filament battery off by the Power switch. The rest do not discharge since there is no emission.