Ultra TR-100 Six transistor radio 1958

The 1958-1960 made Ultra is their first transistor radio using 6 top hat style transistors (Mazda?) made I think and are very reliable unlike the competition at the time, but rarely lasted into the 1960's. It's fair to say the radio didn't work though when it arrived at my door during 'Lockdown' 2020. She has a steam moulded curved edged ply wood cabinet with a rose wood colour finish with a removeable easy access internal framed chassis, just held in place by two Philips screws underneath. The front and rear are made from thick white plastic with a back held in place with 4 screws (missing) so I used bolts. The band switch and on-off volume knobs are push held Bakelite type plastic that breaks easy (so take care). The tuning knob is held with two fixing screws with 1/2 moon recesses at edge of dial for long thin driver.

The repair

I first checked on-off switch, it's a two pole variety, and negative side was reading open circuit. No access to inset cleaner spay, so I drilled a 2mm hole at end and gave the inside a good clean. Problem number one, out of the way! The set uses a 9v centre tapped power supply. These 4.5v batteries are long discontinued and the modern equivalents are large and fairly expensive (£3 each), so I installed a battery box that holds 6x 'AA'  units that cost £2 for 24 (Pound Land). Make sure you get the tree wires the right way around.

Hole drilled in on-off switch to apply cleaner (blue and red wires battery I/P)

One battery's fitted and on-off repaired the radio radio sprung to life. MW was tuned to a weak signal and the MW trimmer capacitor tuned for maximum volume. LW was fine. 

Circuit and print layout for Ultra TR100

Most of the work here would be cosmetic. The tuning knob and control knobs were cleaned in soapy water with a nail brush. It's worth leaving them in the solution for 1/2 hour before to loosen 60 years of DNA from the controls. Brasso was used on the centre facia of dial knob.

After clean-up

When I found the radio the seller had only put this rear as the main photo and one of inside. So once she sent me a front image personally, I quickly made an offer and got the set quite cheap. It was very dull and dusty and the handle had a bodged repair in the past, but I like a challenge.

That brings me to the next job, removing the bronze handle for spaying. Three screws on the inside hold that in place. I stripped it down and sprayed it gold, that matched the brass fittings. I remove the horrible blue plastic wrap that had been fitted as a repair to  the handle and used white insulation braid to put that right, black would have been nicer, but I had a surplus of white, lol Next I removed the circular brass tuning dial. It had turned black with time, but Brasso re-launched it, some thinning of the text was inevitable, but it had to be done.

LED's fitted under brass dial

dial before clean

The on-arrival photograph

The brass dial is held by 3 tiny nails, take care not to damage bras bend brass when removing. I drilled 2 small holes in cabinet and brass to insert the LED's, both in series with each other and a 50 ohm resistor across the secondary of the on-off switch.

I've added alignment details and circuit diagram encase others need extra help. The new battery box I tucked behind a unused bracket in centre of the radio. The way the printed circuit is held in a frank is really quite useful when repairing the set, great design bet adds weight. The radio is quite large for a portable, over 12 inches wide and about 9 tall. The sound quality is nice due to the large size. A 4uF capacitor is fitted across the loudspeaker, I removed it to improve high frequency response.

Inside supported by it's own frame

A short video been added mainly for my Facebook page