Sunday 6 December 2015


I have just given in to the pressure of the last six weeks' relentless TV advertising and decided (with great reluctance - Bah Humbug) that it might be time to turn on the Christmas lights at m0xpd...

As you see, these this takes the form of a 12AT7 double triode.

Obviously, this is all a childish and rather shallow lie - I was using one of the 12AT7's two triodes and the warm, pleasant and (fashionably) early glow is an entirely spurious collateral benefit.

But whatever was I using the triode for in the first place?

Well - life is seldom "One equal music" and I felt I could do with a break from all the endless grind of serious hard work and digital precision. I needed regeneration so, inspired by re-working the PCBs for the next production run of the URMSTON Regen receiver, I took it literally. I made a new regenerative receiver...

I gathered together some pieces of junk, screwed some solder tags into a piece of MDF and hooked up a simple regen. The active device is the "Christmas light" you see above - which was the first triode in the box - which just happened to be a 12AT7.

The results are seen below...

The whole shebang is intentionally "quick and dirty" to reflect my mood - I was trying to leave behind any thoughts of all the rest of the stuff I've been doing for a day or two and just "regenerate". Great fun.

I had already made the plastic "carrier" for the tuning capacitor and the reduction drive, so I could just screw it into this new project. The only less-than-trivial things I did were turning a wooden plug for the end of the water pipe coil former (the work of moments) and making a little mounting carrier / stand-off for the valve socket - similarly a matter of a scrap of PCB material, a drill and a few minutes labour.

Controls are as labelled: a variable capacitive coupling for the antenna, a regeneration level potentiometer and the main tuning capacitor. I am running the 12AT7 on about 40V and the ability to adjust this voltage on the bench power supply is another useful "control". I am taking AF from the circuit into my desktop PC's audio input for amplification - old meets new in a spectacular culture clash.

The original tuning coil (the uppermost of the two windings seen above) placed me in the 2MHz ball-park, so I stripped off wire in-situ, until I could tune to the 40m band.

The first station I heard last evening was Laci, om2vl, in Slovakia. The antenna was the yellow test cable you can see in the photo above - it is about 18 inches long.

Some people just don't get the point of regens. They fail to see their quirky, simple charm. Hopefully those people have plenty to satisfy their (limited) imaginations in all the rather blunt, direct and crude technologies like DDS which feature on many other pages of this blog.

Talking of matters regenerative - I realise that I haven't reported how some folk explored regens in the beautiful surroundings of the Calder and Hebble Canal a few weeks ago...

or - more correctly - they had opportunity to explore building them in the context of the Buildathon at the G-QRP Mini-Convention...

I hope the people who built the URMSTON regen get some pleasure in operating it.

After the Mini-convention, I took off for a week's holiday in North-Yorkshire, staying once again in Whitby. I had chance to go back to Pickering, to put a bend in a new (that's to say, old) fly rod that you will hear about next year. I came back from Pickering to Whitby on the NYMR. I also spent another self-indulgent afternoon at the MPD at Grosmont...

It occurs to me that there's something of an analogy between receivers and locomotives... 

If you "drive" a modern receiver, it is a matter of turn on and go - stable, dependable, accurate. Very much like driving an electric locomotive. If, however, you "drive" a regen, you face an entirely different proposition; you might have a control labelled "Tuning" - but it is not the only control which influences tuning. Rather like a regulator and the "cut-off" on a reverser and (all those myriad other factors that will decide whether or not a steam locomotive will move or continue to move...). 

I like steam engines. Perhaps that's why I enjoy playing with regens. Sometimes. For fun. When I'm not in a hurry.

When I need regeneration

...-.- de m0xpd

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