[codefox1]

Well, it looked pretty good on E-Pay, and arrived as a "Kit" with the cabinet in 4 pieces. A barn special at best. Again, split veneer on part of the top, but at least the buttons are still good. This one has mechanical tuners for the pushbuttons where you tune a station, lock the button by squeesing it shut, and it "remembers" Cool.

Also, this set uses two 1A5 pentodes in parallel for the output. I've never seen this arrangement before in a radio, but with a little digging, I see that there were also Philco's that used a similar arrangement. Why. I'll never know, since each pentode would give .1 watt on it's own. And, remember this is a battery set, wasn't there a better way to do it?

Anyway, one of the 1A5's is missing from the set, and I am wondering if I can get by with just one. I know the volume would be diminished somewhat. I was also thinking about making a socket adapter to run a 3V4 to do the job of both tubes, which would be 100% reversable.

Building a little A-B power supply should be trivial.

I am wondering if anyone out there has tackled one of these before.

Box number 2 of the same auction has not been opened yet. Equally bizarre , I hope. Stay tuned.

[Texasrocker]

Hello Codefox. I looked for the Sparton schematic ( mod 813) in JF Riders, also known as Sparks-Withington chassis, both American & Canadian versions and couldnt find a mod 813 listed. However, since it is a battery-type set, the tube-filament string needs to be complete ( replace the missing tube) before attempting powerup, so the filament voltages "add-up" to correct incoming DC current are correct before attempted powerup at all. Otherwise, you risk the chance of ruining ( burning-out)all the other tube filaments in the filament string in the 1.5 volt types tubes, if your set has those type tube thru-out the circuitry. If you want to use only 1 audio tube, if you have a spare 3V Audio type tube to replace 2- 1.5v types, ( check your RCA tube manual for a good sub), change out to "1" audio-tube (correct socket basing)socket that uses a 3-volt filament audio-tube doing necessary-socket wiring mods under chassis first also. A 3v filament tube will replace 2- 1.5 volt filaments tubes in some sets by careful mods. It would probably be worth your while to check all your tube-filaments with a (1.5 Only) volt battery type continuity-tester, and replace all tubes that have "open" filaments ( if any), and go ahead and add another tube of proper type to replace your missing audio tube before trying any power-up attempts! Those 1.5 v filaments are very-fragile, and can be permanantly damaged very easily! Those type tubes arent as "forgiving" as the 6.3 v types tube filaments for "testing" at all. If you use a continuity-tester to check your remaining tube filaments, make sure your not using a continuity tester powered with a 9v battery! That can fry the remaining orig tube filaments in a heart-beat! The orig 1.5 v tubes are generally cheap$$, except for the 1L6 types. Since I couldnt find the schemat for your Sparton radio, do you have one already? Perhaps I overlooked something here. Just trying to help. Good luck, restoring your vintage Sparton Radio, and yes, building a suitable DC pwr supply isnt hard at all !

[codefox1]

Thanks

It is in Riders vol 10, got the schematic from Nostalgia Air Archives. All the filaments are in parallel on this set, withi from pre-August 1939. It is, of course a battery set and there is a selector for 1.4 or 2 volt feed to the "A" supply. I guess on the farm they would use a lead-acid battery for the "A" supply, and a carbon-zinc battery for the 90 volt "B" supply. When toggled to the 2 volt position, there is a dropping resistor in the set to supply 1.5 to the filaments. Again this is the first set I've worked on that has parallel output tubes, although I've seen plenty of these designs in literature, and have even built a couple of PPP power amps (killers!) It occured to me that being the "hottest" device in the set, perhaps the two tubes were used as a fail safe mechanism to keep the set running for a long time, or maybe the original instructions specified removal of one when operating on a "A-B" battery pack, which there is a plug for on this set. At least the mice who lived inside didn't smoke, so the chassis cleaned up easily.

I'm going to build the power supply from the .gif attached, which I found floating around on the web. It uses the old trick of a 120/220 control transformer wired so that only one leg of the primary is used as the input, the other one is isolated from the line and used as the B source. Only 1 of the secondary windings is used for the filaments, and regulated output voltage is obtained for the 1.4 volts needed for the filaments. Since the amount of current needed for the set is very modest, a small cheap transformer can be used. I've used the same trick on a couple of phono stage projects, and it works out very nicely. DC for the filaments too!

Just waiting for the LM317s to arrive. (I know I have some, but I can't find them.)

If I ever get the cabinet together, I'll post a picture.

[Texasrocker]

Sounds good Codefox! Ive rebuilt several of the old farm-radios yrs ago and have a few in my collection. I built a ac/dc power supply in a old 30s Motorola car radio metal cab ( looks kinda cool), and I use it to power up my old farm sets occasionally. I intend to get around to installing a seperate ac/dc supply into each radio individually someday.
I remember when radio-shack used to carry the transformers in-stock for a few $ ea several yrs ago that worked for these type ac/dc supplies. Im not sure they would still have them anymores. They probably stopped stocking them to make more room in their stores for cell-phones or Ipods.
Sounds like you will be enjoying your Sparton very soon!