SUPER RARE NRG GEM

[teckniqs]

Are you using a switch mode or transformer supply? Love the new meter.

[Elopid]

That looks nicely built it looks good.

[Shedbuilt]

[quote="Techniqs]
Are you using a switch mode or transformer supply[/quote]
The same thing occurred to me, but I'm almost certain from the piccies it's analogue.

Tbh Mr Shed, im gonna have go back through it all from scratch!
Its a strange design and doesnt operate quite like any other NRG ive tested before?
the oscillator section is conventional but then feeds into two bf199s paralleled which from experience is prone to thermal instability?
Its most likely that ive made a blunder in the PA section, but also makes me wonder why Mr Moss scrapped this layout??

If you power up just the driver board (even if it's just by disconnecting the PA from the PSU), and get the radio close enough to get a good signal, you should be able to tell whether the driver board is generating Spurs, or whether it's some sort of self oscillation in the PA. It could be something with the oscillator, or it could be something else self oscillating.

[Albert H]

The pair of BF199s as the pre-driver was a nifty idea that was intended to balance the loading on the oscillator - the balance of the oscillator was crucial (something that Paul still doesn't understand).

You'll probably find one of two things - you might have too much drive to the final (unlikely) or you've got some low frequency oscillation going on in the power supply to the driver or the PA. Check your decoupling / supply filtering. We used to find that 100n in series with 47Ω from the supply end of each of the RFCs (driver and PA) to deck used to tame the LF nasties!

[sinus trouble]

Mr Albert!! Good to hear from you again Sirr!!

I have made some progress with this mysterious VFO! with some much needed help from others on the forum, il upload some more pics!
Do you know the history behind this board?

[Albert H]

As far as the history of this one is concerned - I believe that Stephen built a couple like this to try out his theories. He'd always come up with a paper idea and couldn't ever wait to get it built. We were up all night on some occasions trying things out!

The oscillator was a weird design, based on the "Kallitron" principle, and as long as the sides were dimensionally identical, the transistors were matched, all the passive components were matched and the loading was equal on both sides, the stability was an order of magnitude better than a standard single transistor circuit.

As an experiment, we built one of these oscillators with carefully matched parts and put it in a home made temperature-controlled oven, so that it ran at a very constant 50°C. The stability (once warmed up) was within 1kHz of the 100MHz we'd set it to (chosen because it made the ppm calculations easier!) and it always reached the same frequency every time it was run up! Obviously, this kind of construction wouldn't be practical for Real Life™, but it was a fascinating experiment.

We did other weird stuff too: My idea was to receive 198kHz Radio 4 (which is accurate to 1 in 10¹³), divide it down to a useful reference frequency and use it for high accuracy on Band II, since the DTI had complained about the inaccuracy of some RSL transmitters. One ferrite rod, a lot of very fine enamelled wire, an FET or two for the pre-amplifier, and then a dual-modulus divider to give us precisely 15.625kHz (the reference frequency for the PLL Pro III)..... We set the rig to 100MHz and used it to check the accuracy of a couple of frequency counters! That rig was subsequently used for an RSL, and I was able to demonstrate to the Inspector from the DTI that his counter was wrong!

Thanks for the welcome back, by the way!

[sinus trouble]

Nice one Albert! Its truely inspiring the work you lot produced together! in my younger days it was hard to find someone willing to show how things work? school was a waste of time regarding any serious electronics, wiring up a 12v bulb was the technical limit lol!!
Before the internet? all i had was books and a keen desire to rip things apart and experiment!
My dad wasnt too happy when he came home to find his new radio in pieces!! lol but supported me nevertheless!!!

[Albert H]

There's no substitute for experience!

I started out as a young kid with my Dad's Avo meter, some wire, batteries and light bulbs. I soon discovered electromagnets (wire wrapped around a nail or a screw), and electronics came soon after, when I was given a Philips Electronics Set for my 7th birthday. I soon graduated to building my own stuff, and begged broken radios from neighbours. Some got mended, and the ones I couldn't fix got scrapped for parts.

I discovered the joys of transmitting when I was 11, building a simple "top band" valved AM transmitter, re-coiled to put it into the top of medium wave....

The rest (as they say) is history!