TOWER 5 Transistors Walkie talkies from the 60s - The ones that ignited my radio/electronics hobby.

Tale of my first transmission : 27.125MHz - CB Channel 14.

When I was young (late sixties, first seventies) I got a couple of black TOWER walkie talkies.
They were shiny and looked like rocket science objects.

My actual units

It wasn't long before I realized they weren't usable: communications with a friend were difficult, if not impossible, even between rooms.
On the other hand, however, one evening, I heard voices coming out of one of the radios. They were people who chatted about this and that using esoteric language...as well as coded words (CQ, QTH, QRZ, YL, 88, Roger, K, ...).
I tried to make myself heard, but no one could listen to me.
Suddenly, while I was desperately trying to make myself heard, (are you listening? Hello, ready, are you listening?...) one of those voices answered me. He greeted me, welcomed me and ... explained to me that I had a "super regenerative" radio in my hands and that it could simultaneously listen to many frequencies but only transmit on a single one. That's explained me why I was hearing many voices but I had difficulty make me listen.
After a few days I met that person: he was an OM with a shack that looked like a spaceship to me.
BINGO. Since then I have been CB for years and have become passionate about radio and electronics.
Eventually I also got an ham license.

The radios 

I recently (Jan 2024) bought back a pair of walkie talkies identical to my original ones. I did some research and here are the results:

• they were "Made in Japan";
• they were sold under many brands: TOWER, Bevox, Royal, Teletone, Tempest, Torre Tsushinki Co Ltd, Granada and Caprice;
• they are super regenerative receivers, covering between 26.5MHz up to 29.5MHz;
• when transmitting they output an AM modulated 50mW signal at 27.125MHz (CB channel 14);
  
• There are two models that are aesthetically identical but with slightly different circuit designs. One, identified by model no. 5T-105 (or ST-105) and the other identified by model no. 5T-202 and part no. TR-05. They seem to be one the evolution of the other. They in the RF module; furthermore the first features a single ended AF power amp with a single output transformer, while the former is a push-pull topology with a couple of transformers (one for the driver, one for the output).

    Here are the schematics:

 

Schematic diagram 5T-105 walkie talkie

 Please note as the two AF stages separated by C7 feature an inter-stage DC coupling.

Schematic diagram 5T-202 (TR-05) walkie talkie

Please note as the first AF stage transistors are DC coupled.

Restoration

My actual units are both working but suffer serious problems because of defective push-to-talk switch and volume control. It not only a matter of dirt.. they are mechanically defective.

Volume control

The volume control was first replaced with an external one to prove the internal was bad.
The resistance value of that pot is neither marked on the pot nor indicated on the schematics. With a trial and error approach I've chosen to use 4.7Kohm.

volume pot removed

 

I had been able to procure a new replacements .. but only from China. 

When arrived I had a bad surprise: I ordered 12mm pots instead of 16mm. Uh!

I managed to install one of them, but the result did not satisfy me at all.

So I ordered a 16mm set. Installed, and now they are satisfactory:

 

Push-to-talk switch

To clean and fix the push-to-talk switches I have teared them down to crumbles level..

The surgery was successful, still I am looking (with no success) for brand new replacements. They are 6pdt with 18 pins in 3 lines. Can you help me about this?

That's all, folks!

Emanuele.