R109 Receiver Renovation

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Back in 1969 I bought an R109A receiver from a shop in Bolton that sold lots of ex-government radios. It was Arthur G3JJM that told me about it and he went to buy it for me at the knock-down price of 30 shillings.
The R109 covers 1.8Mhz – 3.9Mhz and 3.9Mhz – 8.5Mhz, I used it as my first receiver and listened on Topband and 80m every night. It was powered by two 6v motorbike batteries that I kept under my bench.

Here I am back in 1969 with my original R109A receiver.

I gave the R109A away after I got a Hallicrafters SX24 receiver. Since then I have never seen an R109A anywhere, I always wanted to acquire one as a renovation project, but they are very rare and although lots of searching over the years I have never come across one…until now!
This started with a conversation on 23cm with Dave G4JLG and Ross G6GVI. I was talking about the renovation of the Eddystone S750 when Dave mentioned that he had an old receiver in his shed that had been there untouched for over 40 years. He had no idea what it was except that it was square in shape. I suggested that it could be a CR100 or maybe an R109 as these were the only ones I could think of. Dave then went down to his shed to have a look, he came back and announced that it was in fact an R109. I nearly fell off my chair!
The next day Dave sent me some photos.

The front panel, almost unrecognisable. Note the yellow ‘T’ this identifies the receiver as a Tropical Version.

The inside of the R109…immaculate!

The outside was a mess and almost unrecognisable with the caked on dirt, however, this receiver is the R109T, which is the tropical version used during the war. When he opened it up the inside was immaculate as it was hermetically sealed, amazing! All the valves and wiring were as new, but there was no vibrator in the PSU. Dave managed to find a couple of old vibrators for me to try. He also sent me a manual and some notes on the R109.

Dave kindly let me have the receiver to be renovated, I couldn’t wait to try it out and bring back all those old memories!

Here I am 50 years on with the R109T ready for renovation.

Now where do I start with this receiver?

Well first of all I need a 6v battery!  A trip to a local motorbike spares shop got me 4AH battery very cheap. That will do fine for testing the receiver.

I removed the front panel from the main receiver ready for cleaning. This took a whole afternoon of scrubbing with warm water, detergent and toothbrush. The muck came off fairly easy and the more stubborn dirt was removed with some Sodium Bicarbonate. I didn’t use any harsh cleaner at all. When it was finished the front panel looked like new, even the decals were intact. The dial, fixtures and identification plate were removed and cleaned separately.

The finished front panel, written in pen on the yellow T is a callsign and name – G3RVR Dennis. Dave G4JLG thinks that this is where the R109 originated many years ago and was given to him.

The PSU is somewhat novel as it uses a vibrator unit in order to produce the HT voltage, also the valve heaters are directly fed from the 6v DC battery that powers the receiver. The PSU is a separate unit that can be powered on its own for testing. Close inspection of the capacitors showed that most of the electrolytics were either bubbled or leaking, so replacing these was my first job. The R109 is very well built, but unfortunately a lot of the decoupling capacitors are not easy to get to. Some are inside the IF cans that are welded to the chassis and others are hidden. I decided that I would replace all the decoupling capacitors that were accessible. It is the same with the resistors, I thought that I would leave them for the time being.

The R109 chassis with the SPU on the left and RF unit on the right.

The next job was the vibrator. I tested the PSU with both of the old vibrators that Dave gave me, but neither of them worked. Solid state vibrators are available from the 19 set group, but they are quite expensive. I did some research and reading about how mechanical vibrators work as well as finding out about the pin-out connections of the vibrators that I have. Taking the vibrators to pieces proved quite tricky, but I managed to remove the cans with a bit of brute force and ignorance! Removing the inside was quite easy and both in good condition. Using my multimeter it was obvious that the contacts of the vibrating bit needed a good cleaning. I spent around an hour carefully cleaning the contacts on one of the vibrators and then tested the unit….it works!
I put it into the PSU and switched on and monitored the HT voltage, then to my astonishment the receiver burst into life! Connecting an antenna brought in stations on both bands. All the controls are working and the BFO is also working, but very weak. The HT voltage is about 150v which is correct according to the manual.
This brings back memories of my original R109, I spent quite a long time trying to improve the receiver by aligning the RF and IF stages. I also added an S meter as well.

The receiver worked fine, but I noticed that the battery was only lasting for about 15 minutes before the HT voltage and LT started to drop. The receiver then began to shut down although the vibrator kept on going. Measuring the current drain on the battery told that it was drawing too much current. After a while the receiver stopped working altogether. After some fault finding in the PSU I realised that a 0.1uf capacitor across the secondary winding of the HT transformer had gone short circuit. After replacing, the receiver worked perfectly, now only drawing less than 2A from the battery.

A bit of touching up with the paint on the front panel, repainting the handles and painting the case green finished off the R109T.

The completed R109T receiver in all its glory.

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