Saturday, April 21, 2012

Topband Transmitter F.G.Rayer

In 1970 just before I got my Amateur Radio licence I built my very first transmitter. The circuit came from Short Wave Magazine and was produced by F.G. Rayer G3OGR. My first attempt was built on an aluminium chassis and my Dad made me a front panel out of mild steel. At the time Neil, G3ZPL had built the same circuit and it worked great! The circuit consisted of an EF91 valve in the VFO and another in the buffer. The Power Amplifier (PA) was a 5763 valve which could run about 15 watt input.

The AM modulator consisted of a 12AX7 (ECC83) and 6BW6 amplifier.


After spending weeks of painstaking drilling, filing and soldering I finally got the transmitter to work, but it had a problem. The VFO seemed to react with the PA. When I tuned the transmitter to the antenna the VFO would pick up spurious signals and shift up the band! Although I had an OA2 stabiliser valve this did not solve the problem. Maybe this was caused by the power supply dropping in voltage when the PA was taking more power.
Later I borrowed my transmitter to George G3ZQS and his antenna got hit by lightning which welded together the vains on the tuning capacitor! Not to mention the Power Supply which 'blew-up' - one of the smoothing capacitors exploded leaving a permanent dint in the roof!
When I got my licence I rebuilt the transmitter with a screened VFO in a separate aluminium box, and an aluminium front panel, this worked really well and was completely stable. The modulator used an ECC83 which had a high gain, I seem to remember using an ECC82 which had a lower gain, but same valve pin configueration.
F.G. Rayer produced loads of circuits and designs for transmitters and receievers in the 1960's and 70's. Almost every month had a design from this guy in Practical Wireless, Short Wave Magazine or Radio Communication. Most were variations of a theme and at the time he was the Enid Blyton of radio. I have to admire Francis G. Rayer, his designs were always well written and easy to follow. I recently found out that he also wrote science fiction books!
Thank you G3OGR!

2 comments:

Jon Hudson said...

just came across this great article when googling for G3OGR. I too built a transmitter, very similar, in 1970 before getting my license in March 1971! I posted a picture of mine on https://www.facebook.com/groups/hamradioconstruction/ and mentioned you - such a coincidence!

73 de Jon G4ABQ

FuzzyUK said...

I remember building something very similar to that too. I finished the front panel with a yukky green colour colour which I originally bought to paint my bike. Those were the days:
http://www.qrz.com/db/G3TFX