Philco model 222
 

Just picked up a Philco 222 in excellent condition. Haven't been able to track down a schematic yet though.

That's a Canadian model not covered in Riders or the other common schematic sources I have access to.

Just Radios should have it, but it's not free: http://www.justradios.com/

Depending on originality and experience level a schematic often is not necessary.

If I have a basic AM set like yours that has never been opened I don't bother to look for the schematic unless a labels missing or post recap/general parts testing there is some odd issue. If as set has been worked on and the work is sloppy or some modification, or there is some tough dog problem that is where a schematic becomes needed.

Of course I can hash out a good portion of the average AA5 circuit (and many other circuits) from tube data and memory of similar schematics...Granted I've probably had 250-500 radios come through my hands, and probably better than 175 cross my bench...When you do that many things start to stick in memory.

Just Radios occured to me. Have ordered hard to find Electrohome schematics from them, lots of parts as well. Great folks to deal with.

This is a battery model.

How easy is it to implement a battery workaround with DC wall warts etc.?

Thanks

Larry

Depends on voltage and what you want...
Most new wall warts are switch mode supplies that create too much noise to use with AM radio (some supplies are so bad they will jam any set in the house even battery powered portables). Also many switch mode supplies are too low voltage.

If you are okay with somewhat complicated design/build work, look for older wall warts that contain an actual 60Hz power transformer. Most radios can be supplied by 2 such transformers and a hand full of small cheap parts.

Make sure your first wart supplies low voltage AC (or crack it open and remove the diodes and cap). Take the transformer out of the second wart and wire it's low voltage winding to the other transformer's low voltage winding, then feed the second transformer's high voltage winging to a diode bridge rectifier and LC filtering (add a LM317/LM337) regulator to reduce voltage if necessary)...That will be you 'B' supply. Add a diode b ridge to the low voltage winding a LC filter and a regulator (same part as above) wired (or made adjustable) to produce the voltage you need for your 'A' supply.

Remember DC rectified from an AC RMS voltage and filtered will come close to being DC(V)=1.414 x AC(V rms).
You want to choose transformer voltages carefully. A transformer has an AC voltage ratio Vout:Vin a typical step down wall wart may be 120V in 7.5V out would be 1:.0625. Your second transformer may be 120V to 12V that would be 1:0.1, but the second transformer is connected 'backwards' (from winding order perspective) and becomes a step up with a ratio of 10:1 so the pair would be (120VAC*0.0625*10)=75VAC RMS which rectified and filtered will give roughly 106VDC (should have about enough head room after being loaded down for a 90V B+).

You can select different transformers for different voltage targets. Always have a bit of head room, watch for sagging, and make sure your first transformer can source ~2-3 times the current the second is rated for on the low voltage windings of both (to prevent the first from overheating).

I greatly prefer designing the supply for more voltage than desired and dropping it to what is needed with a linear regulator like mentioned above it reduces sagging issues and creates a much less noisy supply.

If I had the battery voltages you need (the current draw of the set would be nice to have), a couple of data sheets, calculator, a pen and a napkin infront of me I could design such a beast with schematic and parts list in 5-20 min. :nerd: ...In fact I've done this design exercise before several times for various things. :D

Thanks Tom!

One battery radio I bought a while back had a Permapower Model A converter with it. It has AC in and five DC outlets. Would likely need some component checking but it could be made to work I suppose. Are you familiar with that model or that brand of converter?

You could just go on ebay and find a bench type power supply to use, that way you'd always be able to power up an old battery set regardless of whether it needs 67.5 or 90 volt "B" power.

Eico made a couple of models way-back-when that included 6.3 and 12.6 volt filament taps along with a 0-400 volt variable supply. I haven't looked lately, but I would venture to guess these are still around for a decent price.

I got lucky and bought two of those at a swap meet, earlier last year.
One is just like yours and the other is a Silvertone Powr-shiftr, their spelling.
Look in N/A for Spiegel model A and under Sears for 138****, don't remember the exact number, but there's several versions for different radios and different power inputs.
The "A" supply has large value Electrolytics, at 3 volts, that are really large.
It also has a choke and bridge rectifier.
The older model uses a 6J5 as a B+ rectifier.

The Spiegel number is Model P compact.
The Sears numbers are under Power-Shiftr.
IIRC, there's a schematic inside the cover of unit. :scratch2:

Including the tube compliment would help.

Here's the tube compliment:

1LG5

3LF4

1LA6

1LN5

1LH4

You have 300ma of filament current, the battery eliminator should handle it with the 5 & 6 tube jumper in position.
There's several different versions of those battery eliminators built through the years. The same firm seemed to make them all. :scratch2:

Assuming the filaments are in series, the string would draw only 50ma.

The portables had the tubes in series, the farm radios were all in parallel.
IIRC, in all the real large battery packs the "A" cells were all in parallel supplying 1.5 volts. Those battery packs were really large, heavy and unsuitable for portable use.