British Communications Corporation BCC33 TX/RX

[glowinganode]

Thanks Graham, certainly a nerve wracking experience.
Progress else where has been slow and steady.
Sadly the PA stage had been robbed of its anode choke and various other parts. I've managed to cobble it back together using parts from the junkbox and educated guesswork. As you can see from the photo's, space is very tight.
The anode choke was wound on a home made 3/4" glass fibre tube former, which was fabricated from some tubes which originally came from a load of (tig?) welding torch spares. Two were split and inserted up the middle to re-inforce and over lap the joint.
A single layer winding would not have had enough inductance, so it was wound in 5 sections, each section slightly different to try to avoid undue resonances.
I have now had some HT on it with a 51 k limiting resistor in the screen supply, and using a very un-matched set of 6146's I've managed to get 10 W of rf out which is really promising. It's enough to get on with alignment while I source a new trio of tubes.
Cheers for now, Rob.

[BobGreen]

The first mention of Racal BCC seems to be in 1972. I recall visiting the BCC site near Wembley Stadium in the early 70s to discuss RF power transistors for SSB application.

[brenellic2000]

BCC was formed around 1946/47 by, it is believed, Polish-Jews. Dan D Prenn (of Truvox fame - a Belorussian-Jew) gained a major interest in BCC around 1949/50 - it remained his privately held company and through his RTT/C&C group (it's all explained in my book...!) merged in 1970 with Racal who had sought a merger with Prenn's businesses (Thermionic Products, BCC etc) for his military communications contracts. This was finalised in 1970; BCC's military side remained at South Way, Wembley but a new Racal-BCC business was also formed at Bracknell as part of the new Radio & Communications Equipment and Systems Division - essentially R&D and marketing - under Racal Electronics Ltd... this merger indirectly led to Vodaphone in 1985.

Dan Prenn was a visionary - his family-held business is better known for their Truvox floor cleaners (now owned by the Americans) - hence the book's title!

Barry

[glowinganode]

Thanks both, so definitely pre RACAL then.
Cheers,
Rob.

[glowinganode]

Bit of an update, had a spare evening so set about the RF stage tracking alignment. Firstly it took me a while to realise that with variable permiability tuning the coil is adjusted at the top end and the capacitor at the bottom end which is opposite to conventional variable capacitor tuning.
Finally after a good couple of hours, I had it as good as I could get it, optimised for the frequency ranges I'm interested in. I decided this was a good time to call it a night.
It was a few days before I came back to it and was disappointed to find the receiver was now deaf as a post.
After a bit of sniffing around, the fault was tracked down to the translator board, which mixes the received signal with three different LO's to give the required IF. Being a transceiver, the circuit is bi-directional and so is peppered with switching diodes. At first I suspected tin whisker as I was getting strange voltage readings around one of the mixer transistor, and 10 mA seemed to be disappearing into thin air. Temporarily the earth lead to the can was disconnected, but made no difference. Having spent nearly a weeks worth of evenings going round in circles, I decided the fault must lay in one of the filter modules. This was removed for testing out of circuit and indeed displayed some odd and fluctuating resistance readings. The filter unit is housed in a painted brass can with soldered seams, so a bit of careful brute force and a large soldering iron were required to open it up. Immediately the filter was removed from its can I could see the problem - the can contained about a teaspoon full of water! Normally the filter would sit vertically, so the water would have safely down one end of the can, however to do the alignment, I had to stand the set on one end so the water must have collected in a puddle around the filter assy.
To be continued...

Rob.

[glowinganode]

Have since dismantled the filter unit and found one end of one of the coupling windings had corroded away to nothing. I hope this doesn't become a recurrant problem.
This has since been repaired and performance restored once more.
Some photo's of the filter unit, and one of the PA stage together.
Rob.

[glowinganode]

The set is now virtually finished, and is on soak test while I sort out the cosmetics.
A new metal base cover has been fabricated and cooling fan fitted.
Had a bit of messing around with a really annoying case of feedback when I fitted the cover.
Turned out to be bad earths on a few of the connectors and the pcb mounting pillars. These are stainless steel which are riveted to the aluminium chassis. A couple of these had gone high resistance and were causing "rusty bolt" effects.
This was cured by discharging two very large caps in parallel through the pillar and chassis. After a few zaps, the contact resistance dropped from near 1 ohm to a few milli-ohms.
Thanks for following,
Rob.