From: military-radio-guy Full-Name: Dennis R Starks To: military radio collectors#2 Fcc: Sent Date: Wed, 31 Dec 1997 07:41:24 Subject: Militar Collector Group Post, Dec.31/97 Message-ID: <19971231.074015.4903.0.military-radio-guy@juno.com> X-Status: Forwarded X-Mailer: Juno 1.38 Militar Collector Group Post, Dec.31/97 Index: The AT5/AR8; From Australia, By Steve Hill Vacuum Tubes For Sale or Trade; HUMOR; ******************************** The AT5/AR8; From Australia, By Steve Hill The AT5/AR8 was designed by Amalgamated Wireless Australasia (AWA) according to a Royal Australian Air Force (RAAF) specification. This company (based in Sydney) was a radio pioneering company, and was responsible for a large proportion of Australia's radio production during World War 2. The RAAF specification called for a general purpose 50 watt air/ground transmitter reciever, also to be used for D/F and homing applications. What resulted was a set that was used in a huge variety of applications by all three Australian services, and also by foreign services. The set itself consists of three main units and power supply. The transmitter, receiver and ATU are in boxes each roughly 12x13x10 inches. Power is derived from a separate power supply. The two power supply types were the type G and the type S. The type G runs on either 12V or 24V DC. HT is derived from two motor generator sets. The type S power supply runs on 240V AC, and uses 866s to make transmitter HT and a selenium rectifier for reciever HT. HT is 550V DC for the transmitter and 250V for the receiver. A voltage divider is used to make 300V minor HT for the transmitter. A vibrator power supply is also known to exist which could power the reciever. A junction box was used to interconnect the control signals from the various units. Other units which could connect via the junction box were a remote control unit and a pulse generator. Connections for an intercom system with up to five telephones are provided on the junction box. The AR8 receiver is a MF/HF superheterodyne receiver, and covers the ranges 140-740kc, 765kc-2Mc, 2-20Mc. The unit is fitted with connections for a loop antenna, and can perform DF operations on the MF bands in both AM and CW modes. The receiver consists of two separate tuning sections, one each for the MF and HF bands, mounted next to each other in the upper part of the receiver. The front panel of the reciever is dominated by the two round vernier dials which AWA used in much of its equipment. These tuning units feed into a common IF/AF unit. The front panel has all controls for DF operations, as well as band switches for the MF and HF bands. The MF and HF bands are each split into three sub-bands. Tone and volume controls are provided, as is a BFO pitch control. A primitive front end protection system is also included. The receiver is normally muted by the keying relay which opens the cathodes, but this can be overidden to allow the monitoring of sent signals to be heard. The AT5 transmitter also covers the MF and HF bands. In HF it consists of a 6V6G as oscillator, another 6V6G as the modulator/sidetone oscillator, an 807 as the buffer amplifier, and two 807s as the finals. In MF the HF buffer amp 807 is used as the master oscillator. The transmitter has a VFO, or can operate on one of six crystal positions. Keying is achieved by grounding the cathodes of the valves, which is done by the keying relay. The bandswitch selects harmonics of the oscillator, thus highest power will be achieved on the fundamental frequency (about 50watts). A switch allows the rf signal to be connected through to the ATU, when the switch is off, a resistor is added to the screens of the finals allowing tuning of the transmitter itself to be performed at low power. When the transmitter has been tuned, the rf is switched to the atu, also increasing screen voltage so that full power is output. The atu is designed to handle a random wire on HF, and a trailing wire antenna (longwire?) on MF. A rather large variometer and tapped coil dominates the unit, taking about half the space inside the atu. This is used for MF tuning. The tuning procedure involves first selecting whether parallel, series, or direct coupling is required. Control signals from the MF/HF switch on the transmitter determine whether the MF or HF tuning section is used for tuning. The transmitter can then be tuned by using the antenna tuning and coupling controls. An aerial ammeter gives a tuning indication. The set saw widespread use with the RAAF. I know for certain that it was used in Hudsons, Beaufighters and the early Catalinas. The RAAF also used the set for ground-air control, and in many other ground based applications. For example; No 1 Air Support Unit, Madang ADHQ control tower, 89 OBU for point to point communications. Many larger units used the AT5/AR8 as backup equipment. For example ADHQ Morotai had 4 units for emergency use. The RAAF not only used them in the air and on the ground, but also at sea. The RAAF crash launches used the AT5/AR8. Service was not restricted to the RAAF however. The army version was known as the 112 set. I know very little as to the army use of the set, but I do know that it was used by 9th division signals. It saw applications mounted in radio trucks and also mounted in the back of jeeps. The Navy also used the AT5/AR8. HMAS Diamantina had one as an emergency set in her emergency radio room. I can only assume that this was the case on many other ships, and that the set was used as a primary set on smaller vessels. Many a radio mechanic cut his teeth on the AT5/AR8. One person I spoke to trained on them, and was required to draw the circuit from memory as part of the training. The AT5/AR8 also saw service with the US in a modified form. It was known as the TW12, and was basically a transmitter and ATU mounted together. I believe it was HF only, but can't be sure. Another US version was the AMT150, but I know nothing about this set. The AT5/AR8 also saw service with the British forces, but I don't know if this was official or not. I do know that an RAF unit procured a set to go into a truck as a homing beacon from their Australian counterparts. This was done by swapping it for a peice of their own equipment. After the war, as with other types of equipment, there were large amounts of radios that weren't required. Many AT5/AR8s were used by hams in the fifties. Modifications were available to make them more ham friendly, such as changing the keying system to grid block keying. I have also been told that they were used on commercial airplanes after the war. I have one example of the AT5/AR8, which was my first ever, on the air rig. Initially I used it aboard HMAS Diamantina. When I got my ticket I brought it home and still use it on the air occasionally. I didn't have a lot of trouble getting it going, just an open circuit resistor in the transmitter's oscillator HT line. It uses the 26V type 'S' power supply with two MG sets, and draws about 15A on transmit. I've found the receiver to be quite ordinary. Its not particularly sensitive, and the tuning is too coarse. It drifts for an hour or so after being turned on. I use another receiver whenever using the AT5 (an Admiralty B40 reciever, 1946 vintage), and use the antenna changeover relay in the atu. I don't know how the reciever would be if I serviced it. It's still full of paper caps, and I haven't done on work at all on it. The transmitter is quite good. The VFO is very chirpy, so I have to use crystals which minimizes this tendency. It is only slightly chirpy with a crystal. I've put a zener on the oscillator HT supply which has slightly reduced chirp. I believe the chirp happens for several reasons. The oscillator does not have sufficient isolation. The motor generator set slows down every time you hit the key (ie voltage changes). The oscillator HT is derived by a resistor divider, that is when key up the voltage rises. When the cathode is grounded on key down the voltage has to fall to the 60V ht supply. Thus every time the key is pressed, the main HT voltage falls (mg set), the voltage on the anode falls due to the resistor divider, and the oscillator is pulled. I tried to alleviate this by running the oscillator and buffer amp all the time, and only keying the finals. This removed most of the chirp, however it caused the metering to be interfered with, and running the oscillator tends to deafen the receiver. Thus I use the rig as it was intended but with a crystal, not the VFO. According to an RF power meter I get 45 watts out on 7mhz. I've worked the US using the rig when it was aboard Diamantina. My biggest challenge with the rig came recently. I'm relatively new to radio, and missed out on the valve era by a long shot, so I'm a bit lost when it comes to repairing this stuff. Well, one day I thought I'd give the old AT5/AR8 a run. Fired up the MG sets as usual, put the thing into tune mode. Went key down and the pa anode current meter deflected. Tried to tune it, nothing happened. Hmmm, why is there smoke billowing out the back of the transmitter! The problem I had with trying to fix it (a problem I still have with other broken rigs) was not knowing where to start. I eventually bit the bullet, and decided firstly I'd pull all the tubes, and measure the HT volts. Did this, volts looked OK, smoke still billowing from transmitter. Of course you seasoned valve techs have probably guessed what the problem was by now, but not me. Don't forget this is the first valve repair job I've ever done. OK, I thought. Lets start from scratch and see if the oscillator is working. Put the valves back in (heaters are in series so it wont work without all valves - BTW we don't have toobs in Australia), but no HT on the 807s. Turned a convenient receiver on, and there it was. OK, so the oscillator works, and now I'm stuck again because I don't know what to do next. In desperation I get the transmitter down on the floor so I can see right into the guts of it. After much peering, there it was. A resistor with rather charred looking plastic cover around it. Turns out that this was the screen resistor on the 807s in the finals that's used to drop output power when tuning. The problem, of course, was that the paper screen bypass capacitor had failed. I replaced the capacitor (or condensor as they were called back then) and the set started working. I suspect that resistor has gone a bit high because PA anode current is lower than it used to be when tuning, but its not used when operating so it doesn't really matter. This looks like perhaps a days work, but it actually took me three months to finally find the problem and fix it. I've had a lot of fun with the AT5/AR8. I love to get a bit of history on the air, and there are plenty of hams who are WW2 veterans who used this rig. I have been privelaged to work some of them. They get a real buz hearing their old rig on the air, and so do I. I've no idea how many AT5/AR8s are on the air in Australia. Mine is the only one I know of for sure, but there surely must be others. I just hope that rigs like this can stay on the air for many years to come. I'm doing my best to make sure this one does anyway. Steve Hill VK4CZT 39 Banbury St. Carina. 4152. Brisbane. Australia. ----------------------------------------- Ed) is it possibly the TW-12 Steve mentions in the text is actually the Bendix TA-12? ******************************** Vacuum Tubes For Sale or Trade; 1. (5) Eimac VT-127A, also marked GG1107A. 2. (8) VT-165, also marked 1624. 3. (1) 4E27 4. (2) 249B 5. (1) VT-143, also marked JAN CRC-808. 6. (1) VT-143, also marked CVE 805. 1943 military labelled carton. 7. (1) 2AP1 CRT 8. (3) 3BP1 CRT 9. (4) VT-4C GL-211. 6-30-42 military labelled carton. 10. (2) VT-225 307A 11. (2) FG11 Items wanted: 6AZ8, 6U8A, 12AT7, 6DC6, 6BN8, 6EB8, 6AU6 (For KWM-2A) 516F2 power supply, or the speaker enclosure. Schematics for TRC-77. "Junker" or inoperative GRC-106 amplifier section. Mark Gluch mg60005@sterling-mail.shmi.trw.com ******************************** HUMOR; The following was published in a local newspaper evidently originated in Boise, Idaho. Administratum Alert The heaviest element known to science was recently discovered at the Lockheed Research Center. The element tentatively named Administratium, has no protons or electrons, and thus has an atomic number of zero. However, it does have one neutron, 125 assistant neutrons, 75 vice neutrons and 111 assistant vice neutrons. This gives it an atomic mass of 312. These 312 particles are held together, in a nucleus, by a force that involves that continuous exchange of meson-like particles called morons. Since it has no electrons, Administratium is inert, however, it can be detected chemically as it impedes every reaction it comes in contact with. According to recent discoveries, a minute amount of Administratium caused one reaction to take over four days to complete, when it would normally occur in less than one second. Administratium has a normal half-life of approximately three years, at which time it does not actually decay, but instead undergoes reorganization-vice neutrons, and assistant vice neutrons exchange places, some studies have shown that the atomic weight actually increases after each reorganization. Research at other laboratories indicates that Administratium occurs naturally in the atmosphere. It tends to concentrate at certain points such as government agencies, large corporations, universities, and can actually be found in the newest, best maintained buildings. Scientists point out that Administratium is known to be toxic at any level of concentration and easily destroys any productive reactions where it is allowed to accumulate. Attempts are being made to determine how Administratium can be controlled to prevent irreversible damage but results are not promising. Happy New Year! Ken Sakamoto ------------------------------------------------------------------------------ Nerds in Season... This truck driver hauling a tractor-trailer load of computers, stops for a beer. As he approaches the bar he sees a big sign on the door saying: "NERDS NOT ALLOWED-ENTER AT YOUR OWN RISK!" He goes in and sits down. The bartender comes over to him, sniffs, says he smells kind of nerdy, asks him what he does for a living. The truck driver says he drives a truck, and the smell is just from the computers he is hauling. The bartender says OK, truck drivers are not nerds, and serves him a beer. As he is sipping his beer, a skinny guy walks in with tape around his glasses, a pocket protector with twelve kinds of pens and pencils, and a belt at least a foot too long. The bartender, without saying a word, pulls out a shotgun and blows the guy away. The truck driver asks him why he did that. The bartender said not to worry, the nerds are overpopulating the Silicon Valley, and are in season now. You don't even need a license, he said. So the truck driver finishes his beer, gets back in his truck, and heads back onto the freeway. Suddenly he veers to avoid an accident, and the load shifts. The back door breaks open and computers spill out all over the freeway. He jumps out and sees a crowd already forming, grabbing up the computers. He can't let them steal his whole load. So remembering what happened in the bar, he pulls out his gun and blasting away, felling several of them instantly. A highway patrol officer comes zooming up and jumps out of the car screaming at him to stop. The truck driver said, "What's wrong? I thought nerds were in season." "Well, sure," said the patrolman, "But you can't bait 'em." ----------------------------------------------------- The sex life of an electron. One night when his charge was at full capacity, Micro Farad decided to get a cute little coil to discharge him. He picked up Millie Amp and took her for a ride in his megacycle. They rode across the wheat stone bridge, around the sine wave, and into the magnetic field next to the flowing current. Micro Farad, attracted by Millie's characteristic curve, soon had her field fully excited. He laid her on the ground potential, raised her frequency, lowered her resistance, and pulled out his high voltage probe. He inserted it in parallel and began to short circuit her shunt. Fully excited, Millie cried out, "ohm, ohm, give me mho". With his tube at maximum output and her coil vibrating from the current flow, her shunt soon reached maximum heat. The excessive current had shorted her shunt, and Micro's capacity was rapidly discharged, and every electron was drained off. They fluxed all night, tried various connections and hookings until his bar magnet had lost all of its strength, and he could no longer generate enough voltage to sustain his collapsing field. With his battery fully discharged, Micro was unable to excite his tickler, so they ended up reversing polarity and blowing each other's fuses. What a sad ending! ******************************** EDITOR; Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN military-radio-guy@juno.com When finished reading use browser back button or go to http://www.prc68.com/MCGP/MCGP.html