Vintage Homebrew 80/160M AM/CW Transmitter.

[Racalfanatic]

Hi All,
I picked this transmitter up, on an online auction, a few weeks ago.
It consists of a 12AT7 oscillator, EF91 frequency doubler/buffer, 6BW6 driver, 6BW6 clamp and 5763 PA. The modulator has two ECC83 (12AX7) driving a pair of 6BW6s and modulating the PA through a modulation transformer.
The heaters were wired for DC use, so today I re-wired them for AC and built a power supply meaty enough to run it.
It runs 5W unmodulated carrier and peaks at about 13W with full modulation. You can easily over modulate it!
The VFO has an OA1 stabiliser and it is astoundingly stable.
Here's some photos taken before the electrolytics were replaced and the heaters re-wired and decoupling capacitors fitted.
Who ever built this, did a really excellent job of it.

[kalee20]

Very nice!

I wonder if it was one of F G Rayer's designs? I seem to recall one in Practical Wireless using push-pull 6BW6's in the modulator.

[Brian R Pateman]

That certainly does have the look of FGR about it. My PWs are not easily accessible at the moment but it puts me very much in mind of one that I have seen in one of the early 1960s magazines.

Very nice build quality as Ian has said.

[Skywave]

To me, it looks like it was built - and probably designed too - by a person who was professionally employed in electronics & radio at the time. Obviously I may be wrong, but it just doesn't quite look like a PW / FGR design to me . . . .

Al. / Skywave.

[David G4EBT]

Philpots of Loughborough often made cabinets for popular homebrew projects in those far off days when amateur radio was an experimental, technical and constructional hobby, rather than an 'out of the box' 'plug 'n play' hobby. For example, Philpots did the cabinets for the G2DAF RX, TX, Linear, and they'd do anything to order as a one-off.

Some of FGR's projects were hugely popular.

Many of those who designed and built stuff were ex Services or in the radio/TV trade, and were skilled, and it has to be said, that AM/CW gear was simpler to construct. Components were more readilly avaiable than were commercially made amateur radio gear - most stuff that amateurs used - particularly receivers, had a former life in a military role.

I've lost count of how many 1155s and 1154s I pulled to pieces - sometimes just for vaveholders nuts at bolts. Just ex-WD junk at the time! Happy days.

David

[Racalfanatic]

Thanks for your input gents.
David could well be right about the chassis. The front panel has had a legend removed and it looks like it said "G2DAF". The only badly made part is the top cover which is very flimsy. The VFO housing is very well executed and tremendously stable.
The two panel meters are ex-Air Ministry dated 1942 and 1945, so they were obviously surplus.
The back, of the unit, has an auxiliary B9A socket for an external modulator. The heaters wire wired such that the modulator and transmitter had separate heater supplies.
It makes a lovelly vintage station along with my Eddystone S888A, which is now working properly with excellent stability.

[Ed_Dinning]

Hi Ian, have a look at the designs in the RSGB books of the 60's if you have them. I'm sure I've seen something like this in there.

Ed

[AlanC]

Also, if you've got any old ARRL books- in some ways the design looks to me very American- the paint finish on the chassis, and the use of the term 'plate' instead of 'Anode' on the PA tuning and the meter. Looks beautifully made though, someone took some real trouble over this. I would expect it will work well.

Alan G0NFY

[HamishBoxer]

I would also say looks American.

David GM8JET

[Skywave]

Originally Posted by AlanC

. . . and the use of the term 'plate' instead of 'Anode' on the PA tuning and the meter . . . [looks American]

Alan G0NFY

Indeed! What a give away! (How come I missed that, first time around? ) And that mod. transformer has a certain "USA look" about it, too.

Al. (Skywave).

[Racalfanatic]

But the two panel meters have the Air Ministry markings on them. The valves are all British, as were the electrolytics.

[AlanC]

Ian, agreed- but where did the design come from?? that was my point...

Alan

[Skywave]

Originally Posted by Racalfanatic

But the two panel meters have the Air Ministry markings on them. The valves are all British, as are the electrolytics.

Hmm - I see what you mean, Ian

So - and this is a long shot - it's a UK design, built with UK-sourced parts, but built by someone, living in the UK, but who started life as a USA citizen?
Or perhaps the UK builder simply preferred USA nomenclature.

Whatever, there's a fascinating story hidden in that box of tricks somewhere, that's for sure!

Al.

[HamishBoxer]

Still,very nicely built.

David

[HamishBoxer]

5763 was certainly a favourite back in the 60s.

[RobinBirch]

Very nicely built with an 1154 mag feed meter.