This is one of the first portable transistor radios ever. Although it isn’t a valve set, it’s quite an attractive little thing and I’d promised to restore it for a friend.

  • Circuit Diagram

On inspection I found that the mechanical tuning dial arrangement of pulleys spindles and tension chord had come apart, this was fixed first.

Secondly, it appeared that all of the transistor legs had corroded away, so I was faced with finding the following equivalents:-

V6/R4M (OC44)
V6/R2 (OC45)
V6/R2 (OC45)
V10/50B (OC71)
V10/50B (OC72)
V10/50B (OC72)

The image above shows the original PYE transistors big missing legs

I have found some near replacements on eBay and got ordering.

20/4/20

A pair of OC45 transistors turned up, so I was able to replace the two IF amplifiers. It’s a good thing that they came with long legs because the PCB layout it’s helpful for their leg placement, see the pics below:-

Had to add sleeves to the legs on this one

23/4/20

The remaining transistors turned up and after fitting sleeves to all the legs, I was able to begin refitting.

I was quite methodical with my approach, starting only with the RF transistors, powering up the set and examining the signals with a scope. I noticed that although I could see that the local oscillator was working and that the the actual tuned frequency was present at the tuning cap, I couldn’t see a clean I.F. signal (should be 450 kHz).

It turned out that, by not having the volume control variable resistor connected, the automatic gain control circuit was open and therefore the gain of the I.F amplifiers was off. I discovered this after reconnecting the volume control and the single class A audio driver transistor. Once these were in, I could hear output via a crystal earphone and see a lovely strong I.F on the FFT function of my scope.

This view shows all of the transistors in place. The audio output transistors on the right are in heat-sinks.
This the rear with the back on, the shop it was recovered from is visible in the label top-left.

The cabinet didn’t need much work as it was already in quite good condition. The brass work was cleaned up with wire-wool and WD40. Some small repairs made to the woodwork with superglue, wood glue and some dark wood stain. The top and sides were treated with some Danish oil.

The front face of the cabinet
Danish oil used on the top and sides

Overall, I’m really pleased with this set and will be sorry to give it back to it’s owner.

Radio Playing ‘Five Live’