Pop’s Shed and the Kingsley Radio AR7
After my grandfather passed away I spent a lot of time recalling the good times I had spent scrounging around his CB shack and hanging out with Pop “down the shed”. If you’ve spent time around old motorbikes, retired lawn mower engines, vacuum tube electronics and inches of dust you know what the shed smelt like and probably have a pretty good idea what it looked like as well. I used to be able to send Mum into fits by embedding a combination of oil, grease, dust and grinding compound into the knees and sleeves of my good clothes after spending the day “over south” (South Geelong)
Even now I can still walk into any old auto mechanics and the smell brings back dozens of memories as clear as day … but one memory in particular had been bugging me for a while now. On several occasions I had used a magnificent rack mounted shortwave receiver that had been hooked to a long-wire antenna between the shed and the house. It had several plug in coils housed in bright metal boxes, one for each band as well as a unique tuning dial that had windows around the circumference with numbers that updated as the dial was turned.
|National HRO right? … Nope, its an Australian clone!|
For the longest time I was thinking what you are probably thinking now, I had been using a National HRO receiver right? Well, you’d be wrong … just as I had been for years! When I eventually asked my uncle about the receiver (I waited a long time as I feared it had been thrown out & honestly didn’t want to know if it had) he said, “The AR7?” … “Yes, its here in the garage covered in dust”. He went on to say that I could have the receiver if I could figure out some way to ship it … not a slight problem given the receiver, power supply and speaker are over 120 lbs!
Knowing now that I had been using a completely different receiver I set to work and found out what I could about this National HRO clone …
From : http://www.vk2bv.org/
The AR7 was produced during WW2 by Kingsley Radio of Melbourne for the R.A.A.F. These receivers were used in ground stations for long range communication over fixed circuits as well as for receiving signals from aircraft.
The AR7 was based largely on the National (USA) HRO model, a fact that did not go unnoticed by National. This was the subject of litigation during the war years. Over 3000 of these receivers were produced and for their time, produced excellent performance.
These sets were very popular with radio amateurs after the war and unfortunately subject to many modifications. The Wireless Institute of Australia station, VK2WI at Dural New South Wales was equipped with modifed AR7’s for many years. I seem to remember that very local operators could block the receivers completely, resulting in hurried phone calls!
An unmodified AR7 is a rare beast. The Department of Civil Aviation used these sets for many years in a highly modified form, requiring a new front panel. Refinements included squelch and crystal locked coil boxes.
From : http://www.shlrc.mq.edu.au/~robinson/museum/AR7/
The AR7 is a communications receiver covering LF and HF bands. It was made in Australia during 1940 and bears an extremely close resemblance to the National HRO receiver. The receiver has a tuning range from 138 kcs to 25 mcs, with a gap of 45 kcs either side of the 455 kcs IF amplifier. The internal design is a single conversion superheterodyne receiver with 2 RF stages, 2 IF stages, a BFO and an “S” meter amplifier. The sensitivity is quoted as 1 microvolt. The front panel is stainless steel and it is a very distinctive looking receiver.
It is a good performer, sensitive, has a nice feel, is easy to tune, but hard to find the correct frequency, by reading the frequency from the dial number and coil box graph. It really needs a crystal calibrator. I use it for the weekly W.I.A. (Wireless Institute of Australia) broadcast, so it gets turned on once a week, and is so stable, than I don’t have to retune. It is very clear for AM but a bit fiddly for SSB.
The controls are: RF gain, BFO note, AVC/BFO switch, Adjust “S” meter, Tone, Tuning, Noise limiter, Selectivity, Crystal IN/OUT switch, Crystal Phasing, Audio gain. The Audio gain control has an OFF position which removes the HT so that the coil boxes can be changed.
It has two 6U7G RF stages, a 6K8G mixer, two 6U7G IF stages at 455 kcs, a 6G8G detector/AVC/audio preamplifier, and a 6V6G audio output amplifier. It has a 6C8G twin triode as a BFO and “S” meter amplifier. It also has a crystal filter. The IF alignment should be done very carefully, as any misalignment will reduce the effectiveness of the filter. It is best done with a sweep generator. The 6 volt valve heaters are connected in series, for 12 volt operation.
The external power supply and speaker, are usually mounted in a short 19″ rack, the AR7 at the bottom, the speaker in the middle, and the power supply at the top. The complete unit weighs about 118 pounds. The power supply was switchable between 12v and 240v.
The receiver was used as a ground monitoring receiver for aircraft. It was extremely stable. The model shown has an R.A.A.F. nameplate, and serial number 1786. The manual I have is a D.C.A. (Department of Civil Aviation) version and is a 1947 issue.
It has 5 plug in coil boxes. The coil boxes are: band A 140-405 kcs, band B 490-1430 kcs, band C 1.420-4.3 mcs, band D 4.25-12.5 mcs, band E 12.5-25 mcs. The Army version had an extra coil box covering 50-150 kcs. The large dial is a 20:1 reduction drive and has graduations from 0 to 500. It acts like a flywheel when tuning across the band, and has an effective scale length of 12 feet. The dial shaft goes into a right angle reduction gearbox and has 2 output shafts that drive 2 dual gang capacitors. The graph on the front of each coil box is used to covert the dial reading to frequency.
AR7 nice classic receiver.I have just purchased one myself,needs full restoration.
Over the years it has had every modification possible fortunately there is no additional holes drilled in chassis or panel.Only one coil pack was available with
the receiver LF band.Will be seeking additional coil packs in the future.Well i hope
someone somewhere still has coil packs berried away.
Regards Paul vk5fpwa.
Hi I also am looking for a full set of boxes and also correct HRO boxes (mine uses the boxes with LH panel the frequency curve, RH panel the notes. The serial number of mine seems to maybe have gone with a pot hole being drilled in the chassis!)..I’d had a full unit when a teenager…Norm Beard, the decent secretary of the WIA in Atchison St charged me 10 pounds the lot…a really nice all correct numbers set.
My AR7 came with only one box and was very much modified. Without going through the whole story of searching for the mods…resigning myself to drawing the circuit…after many hours searching last night a web page came up with my set on it…not a copy, the original….along with several other modifications, one a 7 series mod. I printed and saved into favorites. Today cannot refind!!…and it is not in favorites.I’ll keep looking.The box used in the mod is itself mod’d and I’ve not yet checked it but hope it’s the one VK2JZ modified. Pleased to have any communications (and coil boxes). My regards
Hi After fruitless enquiries by amazing stroke of luck found the AR7 I wrote-of was the same set, not a copy, which was featured in AR7 August 1963 , with the numerous mods and circuitry from AS Mather (Silent Key) VK2JZ.I have a few notes from that era so can guide you to the several different mods. Have just bought an original (more or less) AR7 from eBay in working order but needing a good tidy-up. They were an uninspiring under-chassis at the best of times. My latest set came from Gympie originally, I’ll try to get some more history to give it a ‘soul’.
I’d like to get one of the VLF army boxes (50-150kHz) if someone has one. Get in touch if you want, Paul.
Having just lost all my work to a ‘go back and install your info’ command…why can’t you have a site which doesn’t lose all the work when something like that is forgotten…..surely you can fix that, if you think our time has value.
A good read.