Month on the Air is our day-by-day list of what’s happening on air – DXpeditions, Special Event Stations, Contests, etc. Here are the latest two month’s editions.
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Going back to the bad audio output transformer, I gave some thought as to why it had gone bad. Measuring it, not only was it leaking from primary to secondary but the primary was actually open circuit. The thing is epoxy coated and so looks perfect, no signs of overheating.
Those of you who work with valve radios will know of the infamous component known as “that capacitor”. This is the capacitor linking the audio driver valve, from the anode at high voltage, to the grid of the output valve which should be at zero volts. If “that capacitor” goes short or leaky the grid goes positive which turns the valve on hard causing excessive anode current which flows through the output transformer…. which is not designed for such abuse, and lays down and dies. In the worst case scenario the mains transformer and rectifiers can also be damaged. So let us check “that capacitor” in this circuit.
Now that is what I call a leaky capacitor! It might not even be a capacitor any more, whatever, straight into the bin with it.
These two radios both have an intercom audio system as well as the radio audio and both systems use the same pattern transformer in very similar circuits. The other three capacitors in question all read in the low tens of megaohms leakage so all were changed, it is just not worth leaving them in place when a replacement costs pennies.
Why do they fail? There are a number of possible causes, mainly old age combined with old fashioned materials and construction methods by modern standards. Remember these components are knocking on 70 years old, well beyond their design life. And yes, there will be others in the sets in a similar condition but none in such a critical location.
To recap, now both sets are receiving with the same sensitivity. My set does not transmit AM and the ex-Kuwait set has a bad intercom output transformer. Both sets have issues with the in-built crystal calibration system.
As my set does transmit PM and CW there is obviously nothing fundamentally wrong so it is time to think about switch contacts and wiring faults. Ooh look! Our friend Mr. Bodger has been at this set as well, he gets around doesn’t he?
I also found the two wires going to the tuning meter were disconnected. Maybe this is why the calibration system does not work. Then I saw this…
I think our friend has changed the meter but not finished the job. And why butcher the edge of the mounting plate? We won’t ask about the missing mounting studs; the two on the other side hold the plate in well enough. As to why he cut the co-ax instead of unsoldering it, who knows? The end is only an inch away from the cut.
So repair the co-ax, refit the earth tag and reconnect the meter. We now have AM transmit. Result! And there are signs of life on the meter as well now.
The final stage of tuning shows a nice swing of the meter from left FSD (full scale deflection) to right which is correct, it is tuned for centre zero. But the first two stages do not. They use a 100 kc/s (kilocycles per second, this radio predates kilohertz) crystal and according to my oscilloscope it is not oscillating. Swap the module with the one from the other set and all is now hunky dory. One set now fully operational.
The first job is to find where the HV belt is coming from. It happens as the audio gear is plugged in so I opened up the case to look for trapped wires. None were seen, so out with the voltmeter and… look! 175 volts on the headphones! This is not right! In this set there are two audio output transformers, one for the radio and one for the intercom*. Both are floating with respect to ground but do have a common connection. I soon discovered that the intercom output transformer was leaking the 175v HT on the primary side through to the secondary. So, disconnect both secondary wires and all is now good. Very fortunate that it was the intercom, which I can live without, and not the radio side which was at fault.
Looking at the ex-Kuwait set’s power supply I noticed all the spare fuse caps were missing, as was one of the in-use fuse caps. The other two in-use fuse caps were the wrong type. Hmm. Oh look, what should be 1 ¼” glass fuses are in fact mains plug fuses with bits of wire stuffed under them to make them fit. Our friend Mr. Bodger has been here. The in-use fuse with the missing cap should be a tiny wee thing – see the picture with a standard 20mm fuse for comparison. These wee fuses crop up in a lot of Clansman equipment and I have never found a source of them. Chris G6HTH tells me the Post Office used to use them as well.
So, replace the mains fuses with correct ones and power up. I knew the receive power would not work because of the missing fuse but the transmit supply vibrator hums away nicely. So far so good. Fit a polyfuse in place of the missing mini-fuse and power up again. Not so good, the polyfuse trips straight away. Maybe it is the receive vibrator stuck, not an unknown thing to happen with elderly vibrators. The transmit and receive vibrators are the same so swap them over and now there is receive power but not transmit. Open up the vibrator and yes, two stuck contacts. Clean them up with wet and dry (it is nice and thin for slipping between narrow contact gaps) and all is now well, two working vibrators.
This picture shows the inside of the vibrator showing some of the contacts. Note that the case is brass, not the more usual aluminium.
* Being designed primarily for armoured vehicles, there is an intercom system built into the radio so that the crew members can communicate with each other.
With my well-known love of green (ex-military) radios this summer, I came by a C13 set. This is a British Army set in what is known as the Larkspur range, which puts it into use mainly in the 1960s and 1970s. It is of course full of valves. It is a mobile set designed for soft skin and armoured vehicles and is built like a tank. It takes me two hands to lift the power supply and another two to lift the set itself. It is an primarily an Amplitude Modulation (AM) and Continuous Wave (CW) HF set going from 1.5 up to 12 MHz although it will also do Phase Modulation (PM) which the army thought might be useful. It wasn’t. The nominal power output was 10 watts on AM and 20 on PM and CW.
So quite useful for an amateur as it will do top band, 80m and 60m and 40m. And mobile of course if you have a 24v system in your car capable of 6 amps.
The Larkspur range – both VHF and HF – was a major technical advance over previous wartime sets such as the WS19. The cases were hermetically sealed and strong enough to stand on, indeed in a number of armoured vehicles you stand on the radio to get in. All the sets in the range had built in crystal calibrators for their Variable Frequency Oscillator (VFO) tuning, removing the need for separate calibrators for accurate tuning.
Tuning the set is a multi-stage process similar to amateur sets such as the Yaesu FT101. At each stage one tunes the relevant control for a centre zero in the tuning meter. This is unlike the usual amateur set such as the FT101 where one tunes the various stages for a maximum or minimum on the meter.
My set, on receipt, worked pretty well considering the age, one tuning stage does not do the centre zero bit properly and it does not work on AM. CW and PM are OK.
Last week I acquired another one – not for me this time but for the Saladin armoured car at Hever Castle. This set was recovered from a target wreck in Kuwait shortly before the first Gulf War and shipped back to this country. So, plug it in, turn it on and it also works, more or less. It does produce power on AM so there is scope here for making a good one out of the two. It also gave me a belt (175v) so it needs looking into.
Neither have not been opened up yet so watch this space for future developments.
Finally we need an aerial tuning unit for one of the sets if you happen to know of one. Beware, they are hot from a radiation stand point. Do not take them apart unless you really, really have to. And here is one of the beasts, less all the interconnect cables:
Members of West Kent ARS and invited guests celebrated the 70th anniversary of the Society on Saturday the 19th of May. Among those attending was the Mayor of Tunbridge Wells, Cllr. Julia Soyke, who was a special guest at a gala dinner held at the Spa Hotel in Tunbridge Wells, to celebrate the 70th anniversary of the West Kent Amateur Radio Society.
In addition, Mr John Gould G3WKL who is a past President of the Radio Society of Great Britain RSGB, was also present and gave an address following that from the Mayor, recalling his earlier days as a young boy and having been a member of the Society back in the 60’s, he was able to recall many of the founding members.
From copies of the Wireless World magazine, the Society has discovered that a Tunbridge Wells and District Wireless Society was formed, under the leadership of Mr. H. Featherstone AMIEE on the 14th of April 1921, but this appeared to cease in the run up to WWII and the rescinding of amateur radio licences by the Post Office during the time of war.
The current Society was formed after the war in 1948, and a key figure who became President at the inaugural meeting and remained in that post for 21 years, was Mr Bert Allen MBE, G2UJ who lived in Tunbridge Wells.
Bert was a very active radio operator, designer and builder of radio equipment and wrote many technical articles for the RSGB magazine. Other founding members at that inaugural meeting in 1948, included Laurie King G4IB and Frank Barnard G4FB, both of whom were very active in directing the society’s activities in the early years.
West Kent ARS were invited to operate Mills-on-the-Air from Nutley Windmill on Ashdown Forest, over the weekend of the 12th/13th of May 2018.
HF operation with SSB and CW modes, was using an Icom 756 with a doublet that was mainly used on the lower bands due to propagation being poor on the higher HF bands. Operation on VHF was on FM and SSB, and used an Icom 746 with 50w to a 9 ele portable Yagi.
The stations attracted a number of on-air contacts as well as some visitors to the site, despite the appalling wet and windy weather for much of the time.
The Radio and Electronics Fair opened at 10am as scheduled with a long queue of radio amateurs waiting to enter, and over the duration of the event several hundred visitors attended making it a success.
The traders were arranged over two halls, with the photo above showing some of the traders and visitors in the main hall area, though we could have done with more space to accommodate all of the traders that in the end wanted to attend.
Plans are being made to host the REF again near Tunbridge Wells next year, with the date and venue to be confirmed asap so that the event can be placed in your diary and for bookings to commence early in the New Year.
Feedback comments were received from many of those that attended, with the comments below being a small selection;
“thank you for a wonderful day today. Well organised, clean, bright and airy. A good mix of stalls and great catering.”
“A very nice, clean, bright and airy venue with masses of parking. Plenty of traders selling new and second hand gear. Reasonably price food and refreshments”
“Just a short note to say how much we enjoyed the Radio & Electronics Fair today….very well organised.”
“A good day out. If you can get the same mix and number of traders next year that could make this a “must go to” rally in the area.”
The organisers of the West Kent ARS are grateful to all of the traders and visitors that attended this Fair, and we hope that we will see even more attend the event in 2015.
If you have any questions or want to be kept informed of the plans for next years REF, email email@example.com
The West Kent ARS was judged winner of the 2012 Club-of-the-year award for Region 12.
As regional winner, the club was invited by the sponsor of the award – Waters & Stanton, to attend their open day on the 28th of July 13 to receive the winner trophy, a signed certificate and a bottle of champagne.
The club entry that was submitted recognised the increased level of club activities in 2012, comprising more active contesting, participation in JOTA and with special event station operation and the local training that commenced last year supported by a number of local amateurs.
Congratulations to all club members in winning this award through the increased level of activities, and we look forward to developing the club further to build on this recognition.
Further information and photos of the award presentation can be found in this YouTube video of the Waters and Stanton 2013 Open Day, courtesy of Essex Ham.