stewart - warner 300
 

I picked this up at kutztown for 8 bucks, clean and all there except for the tubes. Very good condition set. I hooked up a speaker, put in a set of known good 201's, hooked up the battery eliminator, and was greeted with static.
Could not manage to tune in a station. I assume the center dial is the "coarse" tuning and the others are "fine " tuning. Anybody have any pointers how to tune these?

I believe that one should rotate all knobs in unison so they stay at about the same position then when a signal is heard each one is tweaked seperatly for maximum volume. But what do I know, I've never owned a TRF set that did not have the three tuning caps connected together mechanically. So this procedure is merely a guess.

have you tried hooking up an antenna? IIRC, these sets need an external antenna to pick up much.

Yep, got a 100 foot long longwire outside...

Electronic M is right, you need to keep the three tuning caps in about the same position. Put a strong local station on another radio and look at how the tuning cap is meshed. Then put the three tuning caps on the Stewart Warner in the same position and try. Each will have to be tweaked to max the signal.

This hassle is why the mfrs. worked so hard to get one-knob tuning!

I'll try it tonight, thanks for the tips!

I checked it out more last night and it seems like one of the transformers is not getting power to it.

Sometimes the rosin in the solder used back then was a bit corrosive on the fine copper wire. Sometimes careful resoldering to bridge the break might fix it.

Worked on it tonight, I do have power in and out both transformers. Checked out everything else and did not find anything obvious. 2 capacitors in entire radio. No value listed on them or in schematic. Anyone know what value are these?

Caps are typically 1 or 2 mfd, rated for a couple hundred volts DC. On these 20s radios, typically you'll find the interstage transformers open. There are replacements available-I believe AES sells just the bobbin and windings so you can use parts from your old tf to keep things looking original. You can also bypass your tfs with some common value caps and resistors. I think the Philco repair website has a how to on that.

I did some checking on it tonight, it seems like one transformer is open.

Somewheres on the web I saw an article on using of all things a ringer from an old Ma Bell telephone as a replacement for such transformers.

Antique radios have replacment transformers. I'll have to order one.

Here are the notes on replacing the interstage transformer. On a radio similar to yours, I used modification C:

http://www.philcoradio.com/tech/audio.htm

It kind of reminds me-while most radios of this period are set up like yours, with the last two stages transformer coupled, I have an American Bosch radio from the same period that is entirely resistance coupled. Maybe Wa2ise can explain the advantages/disadavantages of these circuits.

It sings again!
 

Tonight I checked the transformers again. One was open both primary and secondary. The other one just the primary was open. Went to that posted link and bypassed the transformers and tied in the resistors and capacitor.
Fired it up and got stations! :banana:
Next step is to gut the transformers and mount these components in them.

They used transformer coupling in these sets as it gives more gain. R/C coupling will generally give better fidelity but less gain; however, you may be satisfied with the volume you get, and on a typical twenties speaker, the better quality may not be noticed anyway!

The volume is really good, in my opinion. I was surprised how loud it goes.

Are you listening through headphones or a speaker? I've found headphones (especially Baldwin type Cs) much better for critical listening on these 3 dialers.

Thru a speaker, with a good range of volume.

transformer teardown
 

Heres some pics of the transformer, the first is the temp circut I hooked up to test the radio, next is the coil of the tansformer. One winding is broken internally. The last pic is all the pieces of the transformer.
What I'm doing now is cutting the center tab out of each plate, so when it's assembled, it will be hollow to mount the resistors and capacitor inside.

The replacement core should fit on your transformer, as yours looks pretty standard for that era. I've seen little bits of wood used to snug up the fitting between the windings and the laminations. Don't expect a huge difference in performance. I replaced the transformers in a Neutrodyne set, after bypassing the originals with an RC circuit, and didn't notice much of a difference either way.

I'm not replacing the core, I'm putting the RC circut inside the transformer case.

here's he gutted out transormer with the 2 resistors and capacitor mounted inside. I think it turned out real nice.