1948 A.R.C. Tom Thumb Portable Radio

[vortalexfan]

Hello everyone, yesterday afternoon I went to the Antique Mall and picked up an Automatic Radio Company A.T.T.P (Automatic Tom Thumb Portable) Radio from about 1948 that can run off of either Battery AC/DC wall power or Rechargeable Batteries. the "A" Batteries are just normal "C" Batteries but the "B" Battery is of the 67 1/2 Volt variety.

I have 2 issues with this radio:

1.) There is a .02 µF 400V paper capacitor hanging loose on pin 3 of Right rear tube socket (3S4?) and the other side of the cap is cut out of circuit and I can't figure out where it would of went to originally as the Rider's for it is not too clear about the different pins tube sockets, and also there don't seem to be any .02 µF capacitors in this radio according to Rider's only .002 µF or .05 µF in that general area of the radio.

2.) This radio uses a 67.5 V "B" battery assembly which as we all know are no longer available, and I know that with the 90 V "B" Battery you can just Daisy Chain 10 9V Batteries in Series to make 90 V but a 67.5 V battery you have to use 45 "AA" or "AAA" batteries in series to make 67.5 V which isn't very easy to do because most "AA" or "AAA" Battery clips only hold 4 batteries at a time I haven't seen any "AA" or "AAA" battery clips that hold 5 at a time.

My question is, what have you guys done to make a modern version of the 67.5 "B" battery and how do I figure out what the loose hanging capacitor in the radio goes to without access to a very good schematic?

Thanks for your help.

[old_coot88]

Pin 3 of the 3S4 is control grid (G1). The only cap going to it should be the coupling cap from the plate of the 1st audio stage. Maybe someone was trying to hack in a feed from an outside source(?).

[Electronic M]

I have a Motorola radio that used that voltage of battery...I just used the closest multiple of 9V (seven batteries in series). The radio didn't care that it's B+ was about 5V low.

If you can identify cathode(filament in this case), grid(s) and plate leads on the riders and you know the tube is a 3S4 (or some other number) just Google the tube number plus the word datasheet the datasheet will tell you which pin numbers correspond to which elements of the tube. I've done that to figure out blurry/vague riders before.

[jr_tech]

Perhaps make a battery:

https://m.youtube.com/watch?v=j1vMEHobTBc

or buy a replica:

https://www.ebay.com/itm/Reusable-67...edirect=mobile

jr

[Phil]

I use 12 volt batteries, type A23. They are readily available much smaller than a AA and last for a long time when providing B+. The holders are available on eBay cheaply. 5 in series would give you 60 volts which will work just fine. You may find the original battery is still available. The B+ battery for my Motorola Pixie is still available, although they are very expensive.

https://www.lowes.com/pd/Exell-Batte...ies/1000682769

[jr_tech]

Exell also makes a near full size “467” battery, but it is very expensive.

https://www.amazon.com/Exell-Battery...d670b6bc&psc=1

I’m going to try A23s for my next replacement... perhaps two sets if 5 in parallel for longer life.
jr

[vortalexfan]

Thanks guys, I'll see what I can do. Also what is that "white mold" stuff that is all over some of the early plastics like Bakelite in some of these old radios and TVs, and can it be safely and permanently removed without damaging the plastic?

EDIT: After looking around on the internet, I figured out that the tube socket I was looking at with the loose capacitator, it was actually pin 3 of the 1T4 tube that the capacitator was coming off of, and according to the schematic its supposed to be a .05 MFD and someone installed a .02 MFD in its place (they apparently cut out the old one and j-hooked it without soldering, and the other side was to go to ground) there was also another loose cap in the radio apparently that I just discovered a .1 MFD (which seems to be a replacement because the riders doesn't show a .1 MFD Cap anywhere.) Its looking like someone had picked this up as a project and gave up on it.

[jr_tech]

Some Tom Thumb models used a .1 instead of a .05 from pin 3 of the 1T4 to ground.

jr

[vortalexfan]

Originally Posted by jr_tech

Some Tom Thumb models used a .1 instead of a .05 from pin 3 of the 1T4 to ground.

jr

OK, interesting, maybe mine is a newer model that had circuit changes that weren't reflected in the Riders?

Either way it looks like a botched/given up on restoration project, because of the sloppy component placement/hacking going on in the unit.

Also I'm in the process of getting a new furnace installed in my house right now and trying to get my Workshop setup in my new (to me) house that was built in 1921 and it has a couple of work benches intalled in the basement but no electrical outlets installed in them, so I'm waiting to figure out how my dad and I want to configure/install those outlets and some additional shelving to store my test equipment when its not in use, which will have to be a winter project (and also I need to save up some money which right now in this current economic mess we're in is darn near impossible. Lets Go Brandon!)

[dieseljeep]

Originally Posted by vortalexfan

OK, interesting, maybe mine is a newer model that had circuit changes that weren't reflected in the Riders?

Either way it looks like a botched/given up on restoration project, because of the sloppy component placement/hacking going on in the unit.

Also I'm in the process of getting a new furnace installed in my house right now and trying to get my Workshop setup in my new (to me) house that was built in 1921 and it has a couple of work benches intalled in the basement but no electrical outlets installed in them, so I'm waiting to figure out how my dad and I want to configure/install those outlets and some additional shelving to store my test equipment when its not in use, which will have to be a winter project (and also I need to save up some money which right now in this current economic mess we're in is darn near impossible. Lets Go Brandon!)

Now that you have your own place, you can collect all the goodies you want.