19 Set Restoration
As explained on the
Early Years page, a large part of my mis-spent youth was taken up with the
conversion of this venerable piece of WW2 history for use on the amateur bands.
Over the ensuing years, numerous modifications were inflicted upon the set based
on articles written in various periodicals of the day. The entire B Set (VHF
transceiver) and Intercom Amplifier was removed and the space used to
incorporate an anode and screen modulator so that the transmitter could be used
at a more respectable 40W input. Even further atrocities were committed
including the addition of a Pi network for PA matching (using a large variable
capacitor in place of the B Set tuning control) and even a transistor VFO to try
to improve frequency stability! The final insult was removal of 80% of the
moving vanes on the main tuning capacitor in an abortive attempt at bandspread.
At this point, the remains were abandoned to gather dust and eventually carted
off to the scrap heap when I left home for college.
Sadly, I thought nothing of this at the time -
the concept of maintaining an original bit of wartime history never even entered
my head. Furthermore, I had persuaded a couple of my schoolmates to follow my
lead, resulting in the butchering of two more sets.
After many years, completely out of the blue,
I was contacted by one the ex-schoolmates and eventually a re-union was
arranged. An excellent day out was had by all, ending up in his garage where a
very sad looking 19 set brought all the memories flooding back.
"Haven't switched it on for thirty years," he
said "Far too dangerous!" He was right, of course. In those schoolboy days our
fear of electric shock was almost none-existent. We'd get the odd belt and utter
a few curses, but we always seemed to survive (kids were tougher in those days).
It was nice to see the old set again, plus various other bits of equipment that
he had kept over the years. I resolved to look out for another 19 set although I
knew they were a lot more expensive these days.
A few months later, I got another phone call
from my friend. Would I care to go to a radio rally with him at a nearby air
force museum? And, by the way, was I interested in the old 19 set and some of
the other kit, as he wanted to clear out his garage. Well, to cut a long story
short, a price was agreed and I came home with a car full of ancient hardware,
much to the bemusement of my long-suffering wife! The 19set was duly dragged up
to my shack in the loft and the case removed to reveal the thirty-year-old
modifications.
I must say I'd forgotten just what a bunch of
cowboys we were in those days. Some of the wiring was, to put it diplomatically,
less than ideal (especially considering the 500V+ on the 807 anode)! There was
certainly no question of just putting another mains plug on the power supply and
trying it out! Over the next week or so I tidied it up a bit and when power was
eventually applied, the receiver came bursting back into life as if it were last
used only yesterday.
There was a lot of work to do, however. My
friend had done similar mods to myself, except that he had built an external
modulator. The B set and IC amplifier had been removed though, which was a
shame. I still remember that funny valve in the VHF circuit with the two top
caps. It always reminded me of a Dalek from Dr.Who! Luckily he had kept the
B-set's edgewise tuning knob so my first task was to remount it on a bent
aluminium plate in its original position. It didn't do anything but at least it
looked the part! I eventually acquired a pair of NOS 12 pin connectors from an
internet contact and wired them back in place (only problem is they look a bit
too new!).
I also re-instated the old Pye aerial sockets (we had all replaced them
with TV aerial types because we had no idea where to get the matching plugs!).
So now it looks like a real WS19 again - at least from the front. The only thing
missing is the B-set "Quench" control – maybe one day I’ll find one…
The next step was to de-modify the PA output
circuit. All the old components were still there so it was just a case of
rewiring back to the tapped tank coil arrangement. This was done with a little
more respect for the high voltages that would be present!
Restoring the old grid modulation was more of a challenge, however, as the original microphone transformer had been removed. The best I could do initially was to substitute a small low voltage mains transformer using its secondary as the input for a suitably biased carbon microphone. This is incorrect, I know, but at least it would get me back on AM with a reasonably authentic modulation level (I have now acquired an original microphone transformer and fitted it for use with correct dynamic "Microphone, Hand No.7".
Similarly, the receiver output transformer was
non-original, having been replaced with a loudspeaker matching transformer. I
did manage to get hold of a genuine item, but sadly, one of its secondary
windings was open circuit. Currently another speaker transformer is being used,
but at least this one has a third winding so MCW now works again! A replacement
transformer of the correct type has now been acquired (albeit from the Canadian
variant) but this has not yet been fitted.
Time to sort out the power supply. To start
with I had cobbled up a crude arrangement of transformers and solid-state diodes
(ugh!) that at least enabled me to test the set. To be honest this was only
slightly less dangerous than my teenage efforts – still lashed-up on a wooden
board! At the next National Vintage Communications Fair, however, I found the
genuine article. With a bit of haggling I became the proud owner of a PSU No.1
Mk 3 and a matching “dog-bone” lead. I’d always fancied running the set from the
original supply and heard many operators waxing lyrical over the sound of the
dynamotor running up. What I hadn’t anticipated was just how LOUD the dynamotor
would be. I suppose it didn’t matter much using noise excluding headphones in
the bowels of a Sherman tank, but it certainly made listening to the rather low
output from the mismatched speaker a bit of a challenge. And then, when you go
to transmit, the second one starts up….!
I have to admit I have now cheated lightly. I loosened the dynamotor clamps and
inserted some high density foam gaskets. The noise is now just about acceptable.
And I can even operate when the power fails - as long as I remember to keep the
battery charged!
So there we are – at least superficially it’s
back to the original. The set is up and running and seems to get good reports on
the VMARS net on 3615kHz on Saturday mornings. It’s only got 3W output, of
course, but the matched G5RV antenna is something of an improvement on the
original 12ft whip!
