The last thing my wife said to me as I left for Harpenden on Sunday was get me a Decca, I dont know why she said it, its not a KB or ITT.
So when I saw one on the bring and buy I knew I had to buy it.
I have seen photos of these round transistor radios before but in real life they are a lot larger than I imagined, in fact at just over 10 inches across I was beginning to wonder if it was a valve radio. Anyway it is transistor and they are designed to be wall hung in somewhere like the kitchen.
The service sheets say it has the OC44 range of transistors, but this example, which did look original, has all STC types, including the detector diode. The 6 STC transistors were marked Mixer IF IF2 TK1002C TK1002C TK1002C.
On testing the radio there was hardly a click from it when I connected the batteries, which I mistakenly took to be 9v at first.
There was no sound at all, not even a hiss from the speaker. Then I noticed a 100uF capacitor C31 was feeling very warm so I disconnected quickly and went to get the service sheets, better start checking what I was doing I thought..
If you see any of these blue Daly capacitors be very wary they are notorious for being faulty, just as much so as the Callins Capacitors.
It turns out that this radio uses 2 x 6 volt PP1 type batteries, connected in series but with the speaker going to the centre tap.
I changed the faulty cap and tested and changed a few others as well while I was at it.
As I didnt have any 6 volt batteries handy, I decided to adapt the circuit to run from 1 single 9 volt battery. This seemed easily done by the addition of 2 x 220uF capacitors, one from each supply rail to the speaker connection where the common of the original 2 batteries would connect.
The Radio was still dead, but the audio amp was working well. Nothing for it but to start tracing the circuit from the detector back towards the RF. First I checked to see if I could pick up the oscillator on another radio, which I could. So with the signal generator I injected a 472kHz signal to the IF side of the detector, nothing.
I tested the diode and it was open circuit. Detector diodes do go faulty from time to time but this was the first time I had experienced it.
I had an OA81 so fitted that in the circuit and was greeted with radio signals, rather quiet and a little distorted.
Slowly the radio started coming to life and the volume and quality improved dramatically.
I decided to leave the radio working on a single 9v battery and made a more permanent job of fitting the 2 capacitors. As the radio only draws just over 10mA quiescent current the PP3 battery should have a reasonable life.
Someone in the past had made an attempt at fixing the circuit board, which had obviously come adrift in the case, by drilling 2 holes through the front and using a couple of rusty screws through from the front of the radio. I made a slight improvement on this by glueing a couple of wood support/spacers for the board to be supported on. I found a couple of nice chromed domed head screws and used these to bolt through the front, spacers and circuit board.
After a clean it looks a little more respectable, and is working very well.
This seems to be another radio which I cant get to cover the full HF end of the MW band. I thought I had found the issue when I noticed the moving vanes on the smaller oscillator section of the tuning cap were not aligned with the other larger section, they were still slightly meshed with the fixed vanes when the cap was fully open and the aerial vanes were unmeshed.
I was able to force the vanes back into alignment as they were able to be rotated on the shaft, with a bit of effort, this helped the HF coverage but still not able to tune high enough to get Gold on 1548, the limit is Lyca Radio on 1458. Oh well never mind the wife doesn't listen to Gold anyway.
Mike
So when I saw one on the bring and buy I knew I had to buy it.
I have seen photos of these round transistor radios before but in real life they are a lot larger than I imagined, in fact at just over 10 inches across I was beginning to wonder if it was a valve radio. Anyway it is transistor and they are designed to be wall hung in somewhere like the kitchen.
The service sheets say it has the OC44 range of transistors, but this example, which did look original, has all STC types, including the detector diode. The 6 STC transistors were marked Mixer IF IF2 TK1002C TK1002C TK1002C.
On testing the radio there was hardly a click from it when I connected the batteries, which I mistakenly took to be 9v at first.
There was no sound at all, not even a hiss from the speaker. Then I noticed a 100uF capacitor C31 was feeling very warm so I disconnected quickly and went to get the service sheets, better start checking what I was doing I thought..
If you see any of these blue Daly capacitors be very wary they are notorious for being faulty, just as much so as the Callins Capacitors.
It turns out that this radio uses 2 x 6 volt PP1 type batteries, connected in series but with the speaker going to the centre tap.
I changed the faulty cap and tested and changed a few others as well while I was at it.
As I didnt have any 6 volt batteries handy, I decided to adapt the circuit to run from 1 single 9 volt battery. This seemed easily done by the addition of 2 x 220uF capacitors, one from each supply rail to the speaker connection where the common of the original 2 batteries would connect.
The Radio was still dead, but the audio amp was working well. Nothing for it but to start tracing the circuit from the detector back towards the RF. First I checked to see if I could pick up the oscillator on another radio, which I could. So with the signal generator I injected a 472kHz signal to the IF side of the detector, nothing.
I tested the diode and it was open circuit. Detector diodes do go faulty from time to time but this was the first time I had experienced it.
I had an OA81 so fitted that in the circuit and was greeted with radio signals, rather quiet and a little distorted.
Slowly the radio started coming to life and the volume and quality improved dramatically.
I decided to leave the radio working on a single 9v battery and made a more permanent job of fitting the 2 capacitors. As the radio only draws just over 10mA quiescent current the PP3 battery should have a reasonable life.
Someone in the past had made an attempt at fixing the circuit board, which had obviously come adrift in the case, by drilling 2 holes through the front and using a couple of rusty screws through from the front of the radio. I made a slight improvement on this by glueing a couple of wood support/spacers for the board to be supported on. I found a couple of nice chromed domed head screws and used these to bolt through the front, spacers and circuit board.
After a clean it looks a little more respectable, and is working very well.
This seems to be another radio which I cant get to cover the full HF end of the MW band. I thought I had found the issue when I noticed the moving vanes on the smaller oscillator section of the tuning cap were not aligned with the other larger section, they were still slightly meshed with the fixed vanes when the cap was fully open and the aerial vanes were unmeshed.
I was able to force the vanes back into alignment as they were able to be rotated on the shaft, with a bit of effort, this helped the HF coverage but still not able to tune high enough to get Gold on 1548, the limit is Lyca Radio on 1458. Oh well never mind the wife doesn't listen to Gold anyway.
Mike
- you only get five for a pound now instead of six, so, considering the much longer life you can expect from AAs, they still only cost £1.60 for 8. How much do you pay for your PP3s?
