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AT5/AR8 in USA
The wireless forum is rather slow needs some input
This is an interesting thing . An Australian WW2 era radio on the air in the USA . The radio set was made by AWA in Sydney , primarily intended for aircraft like the Wirraway , Hudson and others . It was also issued to the army , the army nomenclature, WS 112 . AWM pics depict these sets in use in the SWPA mounted in Jeeps . And the Chevy Aust. signals van . And small vessels .... air sea rescue maybe Mike Thought you'd find this of interest.... -----Original Message----- From: milsurplus-bounces@mailman.qth.net [mailto:milsurplus-bounces@mailman.qth.net] On Behalf Of David Stinson Sent: Tuesday, April 17, 2012 1:39 PM To: milsurplus@mailman.qth.net; ARC-5 List Subject: [Milsurplus] Progress on Auzzie AT5-AR8 Set The WWII Australian AT5 / AR8 set is on-the-air, transceiving and making contacts. I have had a great deal of help from our Australian members, for which I am very grateful. http://home.netcom.com/~arc5/AR8AT5/AR8AT5.jpg Above the transmitter is a temporary junction box I built to provide microphone bias, antenna and RX/TX switching. I've connected them for 12 VDC operation. The AR8 receiver is powered at 90 VDC using a homebrewed, regulated 12V-to-90V DC/DC power pack. The radio has excellent, loud audio and good operation. I see no reason to pound the old veteran with 250 V so I intend to keep it running at 90V, even if I am fortunate enough to acquire an original power supply. I'll just regulate it down. The AT5 transmitter is running at full 550V B++ and 300V B+ using a rebuilt Hallicrafters 12V mobile supply. While I have the normally-included external antenna tuner unit which, in the original installation, handled antenna and T/R switching, space is unavailable in the upcoming display to include it. Adding the third box would give a footprint half-again bigger than an ART-13. I need them operational for HamCom, so I built a small external junction box to handle these functions. When I build the permanant rack for my station, I plan to install the ATU on a shelf above the TX/RX, similar to this installation in an RAAF rescue launch: http://home.netcom.com/~arc5/AR8AT5/..._AR8Launch.jpg Here is a diagram of the homebrew switching box: http://home.netcom.com/~arc5/AR8AT5/AR8AT5JB.jpg Notes on the AR8: I went through this set several years ago and it's been in the "Round Tuit" que until now. IIRC, every cap in it was good. If I changed any, it was one or two. It needed the usual lubrications and De-Oxits. The MF dial is cracked so I reenforced that. The BFO needed to be re-centered, which was easy. The dial calibration on HF is a little off. Since it needed no other alignment, I decided to leave the glyptol-locked adjustments alone and live with a little "mental correction" on the dial reading. Replaced a couple of short "rotten insulation" wires. One curious thing: The filaments are strung to either be wired for 24V or 12V, DC or AC. When running them 12V, the manual calls for power pin 1 to be A+ and to tie pins 3 and 4 together for A-. These A- leads get "earthed" in the external power supply. However- in my set, if you connect it this way, the chassis becomes +12 volts to "Earth," and if you ground pins 3-4, you have a short. I don't know why yet. I simply reversed the wires, using 3-4 as A+ and 1 as A-. This worked fine and there's no electrical reason not to connect it thus. It's actually OK with me, because I had to do exactly the same thing with the AT5 transmitter, but for other reasons. Notes on the AT5: Unlike the receiver, the AT5 required a nearly complete re-capping. The original antenna connector is broken, so I've installed a temporary "N" connector (no metal changes, of course). I put a small screw between two turns in the tank coil, effectively removing a turn and making the tank suitable for loading a 50-ohm antenna: http://home.netcom.com/~arc5/AR8AT5/AT5TANK.jpg This delivers 25-30 watts of grid-modulated AM and 50-60 watts of CW out to my 50-ohm dummy load. Rig is chirpy on CW, even when running original crystals. I haven't looked into that yet. In the original design, the microphone element is not run against ground; it is series-connected between the microphone supply in the external power unit, the microphone element and the microphone transformer primary, which then goes to "earth" via the A- and thus "earthed" filament string connection to power connector pin 3. U.S. designs place the microphone power running through the mic transformer, a dropping or divider resistor, then the microphone element and thence to ground. Since I'm using one of the microphones I have on hand, I connected power pins 3 and 4 to A+ and pin 1 to A- (the manual calls out the opposite) and that provided A+ through the mic transformer primary, out to a voltage divider/audio bypass and then through the mic element to "earth." This worked well with good modulation and plenty of audio and the filaments operate either way. The transmitter VFO is surprisingly stable after warm-up. For Safety's sake, I will be adding one actual modification: if the plate blocking cap, C24 leaks, B++ will show up at the antenna connector. I'm going to add a 2.5 mHy choke from the antenna connector to ground so any such leakage will be safely shunted. One problem I have run-into: a low-frequency parasitic oscillation which is creating low-level "spurs" either side of the carrier. You can see it on the monitor scope and hear them on a monitor receiver. While I haven't worked on this yet, I'd bet coffee and donuts the problem is the missing transmitter case and covers. All these long cables running around and next to the PA are causing low-frequency feedback. Covers for these sets are made of "unobtainium" so I'm going to fabricate covers for the transmitter and watch the parasitic go away... I hope ;-). Speaking of parasitics, I need some advice: The PA plate leads lack VHF parasitic suppressors and are made in such a way that it would be destructive to attempt to insert them at the plate caps of the 807s. Should I decide they're needed, I'm thinking small ones in the cathode and/or screen leads would work as well. What do you think? Now to build the display stand and work on those covers... 73 OM DE Dave AB5S P.S. More AT5 / AR8 operational photos, courtesy of our Australian members, at: http://home.netcom.com/~arc5/AR8AT5/oppics/ __________________________________________________ ____________ Milsurplus mailing list Home: http://mailman.qth.net/mailman/listinfo/milsurplus Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Milsurplus@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html _____________________________
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1940 cab 11 C8 1940 Morris-Commercial PU 1941 Morris-Commercial CS8 1940 Chev. 15cwt GS Van ( Aust.) 1942-45 Jeep salad |
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....also supplied to US Forces under Reciprocal Lend Lease (RLL) arrangements.
Mike C |
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Yes
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Ah yes , true The Australian radio industry manufactured various equipments for the US forces in the SWPA. A few Aust. sets have turned up in the USA . And, one of the GMH ambulance Jeeps has turned up over there as well . Seems like the yanks took a few things home when they left. I have seen US army markings on these Aust. radio types AWA AT21 AWA 3BZ AWA AMR 101 Radio Corps. ATR4 I believe they also used the locally made mobile radar sets , because they were better than the US made sets. There was a few articles published in EA magazine years ago on this topic, the Aust. designed and built mobile radar sets were considered the best . Until the rest of the world caught up and overtook . Mike
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1940 cab 11 C8 1940 Morris-Commercial PU 1941 Morris-Commercial CS8 1940 Chev. 15cwt GS Van ( Aust.) 1942-45 Jeep salad |
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Ah, yes, the LW/AW radar sets (Light Weight/Air Warning), super-secret at the time, and mostly destroyed rather than sold off at Govt auction when no longer required. Thankfully one set survived, and is now on display at the AWM in Bradbury Aircraft Hall. They were 'super secret' because of the cavity magnetron that was the 'heart' of the system. Old hat, now, of course: every microwave oven has one, but not so at the time.
The RLL scheme was interesting and the range of things Aust supplied to US forces is astounding, including all those radios and radar equipments you listed above. I seem to remember that Australia supplied 3/4 of the US$ value of Lend Lease items received, back to US Forces as RLL items: everything from clothing and food to small ships. The books were still in the USAs favour, of course, but not bad for such a small population with a relatively narrow - and small - manufacturing capacity. Interesting thread, Mike. Mike C |
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