Look what I dug out of the internet

[MiXiN]

Hollings' version of the PLL has a missing "balance" transistor. There should be four transistors in the oscillator stage - the two that generate the ½f signals and two buffers - one of which feeds the PLL and the other just provides a balancing load to ensure that the two signals are exactly equal, thereby giving the cleanest possible signal at the output frequency when combined. The PLL Pro III uses a pair of FETs for the buffers, earlier versions use BF199s (or even BF494s on the really early ones).

Hollings didn't understand the operation of the oscillator, and how essential accurate balance actually is. If the balance is degraded, lots of ½f breaks through, and there can also be an amount of 1½f as well.....

Thanks for the reply, Albert.

Upon inspection, the Oscillator stage in my PLL3 only has 3 Transistors like the version above, so it's an Hollings variant.

With regards the PLL unlock LED not fully extinguishing even when the board is in lock, where do you think I should start looking for the fault? I'm thinking a leaky collector/emitter junction on the Transistor that drives it, but apart from that I'm not sure where to look?

When in lock, the PLL lock LED is fully lit, and the PLL unlock LED is around 50-60% brightness simultaneously.

Operation appears fine, but it's just an annoyance.

I'm not sure on this, but I think it may be normal for the unlock LED to stay partially on. Are you (frequency tuning wise), in the middle of the oscillator's lock range ? I tend to doubt a leaky LED driver transistor, especially as the LED brightness is varying. I'm more inclined to think that the transistor is being held partially on.

I had one of these drivers a while ago, and I'm pretty certain the unlock LED was fully extinguished when in lock.

I'm doing this at around 100Mhz, so I'm roughly in the middle.

I'll have to get a voltmeter on the base of the unlock LED Transistor to see if it's partially biased, hence the LED being lit.

[Shedbuilt]

Thanks for the reply, Albert.

Upon inspection, the Oscillator stage in my PLL3 only has 3 Transistors like the version above, so it's an Hollings variant.

With regards the PLL unlock LED not fully extinguishing even when the board is in lock, where do you think I should start looking for the fault? I'm thinking a leaky collector/emitter junction on the Transistor that drives it, but apart from that I'm not sure where to look?

When in lock, the PLL lock LED is fully lit, and the PLL unlock LED is around 50-60% brightness simultaneously.

Operation appears fine, but it's just an annoyance.

I'm not sure on this, but I think it may be normal for the unlock LED to stay partially on. Are you (frequency tuning wise), in the middle of the oscillator's lock range ? I tend to doubt a leaky LED driver transistor, especially as the LED brightness is varying. I'm more inclined to think that the transistor is being held partially on.

I had one of these drivers a while ago, and I'm pretty certain the unlock LED was fully extinguished when in lock.

I'm doing this at around 100Mhz, so I'm roughly in the middle.

I'll have to get a voltmeter on the base of the unlock LED Transistor to see if it's partially biased, hence the LED being lit.

By the middle of the lock range, I meant the variable element of the VCO tuning (variable cap or variable resistor), the centre of where it drops out of lock on one side, and where it drops out of lock on the other side.

[Shedbuilt]

I think you might well also find, that oscillator balance, may affect the extent to which the unlock LED dims.

[Albert H]

Basically, the H******s version of the circuit doesn't work properly (and can't ever work properly). It might be worth adding (point-to-point) a balance buffer to see if it's possible to clean up that mess. However, that version drives the final stage into saturation in an effort to make it "no-tune", so its output is very "harmonically rich" (a euphemism for "dirty as s**t"!!). It's probably best stripped for parts, and a competent design constructed from the wreckage!

[Shedbuilt]

Agreed all round Albert. A retro fitted buffer would have to be point to point as you said I think, because when he decided the buffer was "unnecessary", it looks like the tracks were removed, and the board made narrower. Wiring it point to point (done well), would probably help with balance I'd think. In the original of course, Stephen Moss had visibly gone to a lot of effort, to make the PCB tracks for the oscillator, including the buffer and its mirror, symmetrical; quite possibly selected some of the components for matching too.

[Albert H]

I can confirm that the oscillator components were chosen - the transistors (for example) were supplied with a little blob of paint on top. You used the white marked ones in the oscillator pair (they were matched for Hfe and saturation voltage to within 0.5%). The transistors were selected by hand from a huge bag of thousands of them!

On the Pro III, I suggested using FETs for the buffer transistors (to reduce loading on the oscillator), and we found that we could get pretty good fundamental suppression by using just one FET buffer, but the results were still much better (by over 18dB) if we included the "balance" stage. You'll notice that the layout is exactly symmetrical - this was also found to be best. The six two-turn coils were machine-wound (by a company that made industrial springs!), and were all absolutely identical. When correctly assembled, the fundamental suppression was over 60dB, and the highpass filter at the oscillator output helped a bit more.

As an aside - I used this "Kallitron" oscillator configuration in a commercial exciter design, but used inductive coupling for the PLL input (it was simply convenient) and physically smaller coils (though with more or less the same inductance). The output of the oscillator was taken through a little ceramic bandpass filter (the Soshin ones) into a buffer stage, then through another bandpass filter. The purity after the second buffer was exceptional, with all other products better than 92dB below the carrier! In this instance, we used a TSA5511 PLL IC, because we could configure the same board layout for any frequency from around 45MHz right up to nearly 1GHz! The PCB tracks formed Lecher Lines at UHF, and conventional coils were used for lower frequencies. The gain of the second buffer was voltage-controlled, allowing an AGC function to provide the right drive level to the next stage. The output of the second bandpass AGC/filter fed a FET amplifier stage for 10 Watts output at pretty much any frequency up to 400 MHz, and 6 Watts above that. The first buffer stage could have its output switched off to provide out-of-lock carrier switching.

The other difference between our Kallitron and the NRG one was that we used a separate modulation varicap, because we could scale the bias voltage to give the same modulation sensitivity right across the band, allowing the same modulation depth control circuit to be used without adjustment at any frequency, completely preventing over-deviation, and without the PLL loop filter compromising the modulation frequency response at all!

Our exciter was as complex as the Rhode & Scwartz exciter product (that used the same PLL with a more conventional oscillator), but had a purity that was >12dB better than the R&S product!

[Shedbuilt]

Pyers was very good at copying Kenny Myers' gear!

Just had a flashback to some of Kenny Myers’ boards, bearing the words “Yes Eric, it’s another one”

[Albert H]

There were other messages on the "Myers" boards too.

Do you remember another builder from that era who used to use a penny dated for the year of manufacture, glued to the box of his rigs near to the output socket?

Just for the sake of amusement (and to show that my gear was worth rather more), I did a short run of rigs with 10p coins (of the appropriate date) glued near to the output socket.

I received one of these a few months ago to have its PLL reprogrammed to move it a couple of MHz down the band. I was astonished to see that it was dated 1981, and still produced its original 95 Watts! It was filthy (covered in brick and cement dust!), but was still working because it wasn't fan-cooled - it just had a big heatsink! Opening it up revealed that it was perfectly clean inside, but the "indelible" ink markings on the programming diode points on the board had faded. Other than that, it was just as it had left the workshop. A quick check showed that it had moved about 6 kHz low of its marked frequency - not bad for 42 years old! I moved the programming diodes and slighly peaked the doubler and filter stages, and it gave 96 Watts on its new frequency, with no extraneous products worse than -72 dBc. I also tweaked the reference oscillator trimmer to put it bang on its new frequency.
That particular rig (and its three predecessors) had been used at weekends for a couple of years. It was the last of its series, and the station closed down in 1984. I've been trying to remember the name of the station for a couple of months....!

[Shedbuilt]

There were other messages on the "Myers" boards too.

Do you remember another builder from that era who used to use a penny dated for the year of manufacture, glued to the box of his rigs near to the output socket?

Just for the sake of amusement (and to show that my gear was worth rather more), I did a short run of rigs with 10p coins (of the appropriate date) glued near to the output socket.

LoL. Nice touch. I jokingly talked (over a few beers), about using the alter ego / nom de rig, of “Chris Moore-Miles”.

Another trademark I remember seeing a bit later, was “Sprogtronics - still copying things”. That cropped up on a nicely built and implemented rig. The exciter and PA were on nice, neat PCBs, stable, filtered. It had a band I receiver which looked out of place; messy dead bug, but a competent design, with sensible layout, so worked fine. That rig stands out, because it was the probably the most powerful MOSFET output device I’d aeen at the time (I’knew they existed; the MRF141, 151 etc, had been around for a while, just hadn’t seen one for myself), and gain of about 16dB; from 2W to about 80W in one stage was impressive then.

[Albert H]

That's quite amusing. I built my first VHF FET rig (MRF150) in the late 80s. A certain gentleman with an unpronounceable African name used to go to his rival's sites and push drawing pins into their coax, blowing up their rigs and taking them off air. When he tried that with the MRF150 rig, it kept going and gave him a really severe RF belt through the drawing pin. The burn was so bad that he never tried that trick again!

On the subject of unusual rigs, there were a whole series of late 70s / early 80s Invicta rigs that had a weird transistorised exciter, on a square board, with a tall central coil former on it with three or four coils on the same former.... The output of that board then went into another compartment of the rig, with a QQV06/40 valve for the output stage! These things used to push 80 - 100 Watts, and on the relatively quiet band in those days, with a well elevated aerial, they'd cover much of London - often in stereo. Their programmes used to come from reel-to-reel tape recorders which they left up the block with the rig!

[radium98]

it kept going and gave him a really severe RF belt through the drawing pin. The burn was so bad that he never tried that trick again!

how did you know that .

[Albert H]

Simple - the guy who was with him up the block told everyone about it!

We used to take all sorts of precautions to prevent having the rigs crippled by malign action:

• We buried them in walls, with the cables running inside the brickwork
• We ran the aerial feeders inside the masts.
• Several rigs were built with the PA inside the mast!
• Rigs were put in inaccessible places, including inside water tanks (!), screwed to the underside of water tanks.
• Liberally infecting the cases of rigs with Shigella - anyone who touched the gear would regret it for several unpleasant days!
• Installing sacrificial "dummy" rigs that could be easily located, and when disconnected turned off the real gear (Gotts impounded any number of dummies!)
• Lots of other tricks - many of which are still in use, so I won't give details!