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Thread: Motorola MOTRAC

  1. #1
    August Johnson No Longer Registered

    Default Motorola MOTRAC

    I have this old UHF 80 watt MOTRAC T64MST-3100A that I'd like to make work again for some strange reason. I've got the complete system, radio, cable, mic, speaker and control head. Does anybody know if it's at all possible to get these to move into the 440-450 Ham band? I also have the problem that I have to get into this thing, something is broken, the key turns but it sounds like something is not engaging and the lid won't unlatch.

    August Johnson KG7BZ


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    Welcome August.

    Motracs - I wouldn't attempt to move it out of it's current band. It's a crystal set. MST may even be new enough to have channel elements. So, that's your first challenge - finding crystals. You'll want a manual too so you can wade your way around it's circuit boards and point to point wiring.

    Locks - the radio slides into the mounting tray. The key turns a simple blade latch which you can see on the bottom whether it's engaged. Sometimes the trays were really tight, and it took some judicious prying with a screwdriver to get off.

    Good luck with your Motrac. They were a real workhorse, and I worked on far too many of them to ever want to see another personally. But, cleaned and painted, they were an impressive looking piece of iron. Now you need a 65 Fairlane to go with it.
    Bow wow wow yippie yo yippie yay

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    Those cases were always a pain to get off.

    but I agree with not touching it. Channel element type and very expensive to re crystal and change PL codes. Forget about DPL

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    the lock engages the base tray. you may have to take off the front if that is broken.
    I think there was four screws that held on the front and you may be able to work that off if you can tilt the top away from the radio

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    The transmit side is fairly simple, with a hand full of padding capacitors to get max performance. But if you are only going down to 448 or 449 for TX you likely won't need to do that. The real problem is the receiver - those used the "old time" engineering design of filtering the incoming RX signal first, then amplifying it, so as to not be amplifying all the adjacent junk unnecessarily. Most receivers today go the other way around, amplify first and then filter out the unwanted stuff. Any how, the front end preselector assembly, a cast metal container with 5 coils in it that comes from the T/R relay, is extremely sharp in cutoff as the coils are very large and therefore high "Q". You will not get much in the way of sensitivity below 449.5 with the normal 450-470 range Motrac. For this reason, those of us that were on the air back in the early 70's before you could buy appliance radios at the ham radio store, we set up the repeaters for LOW input (444) and HIGH output (449). Got things going easily but later on caused some upset with the powers that wuz about having low input instead of high input. If you need a manual PM me with the full model number (U44HHT/LHT/MHTxxxx), I have most Motrac/Motran manuals although not so much for UHF, and I'm not expecting to be needing them any time soon. As far as the key, Bill is correct - just look up at the bottom of the tray below the key and see if the locking cam is swinging out of the way. The top cover and lower tray are probably just good and stuck - they used to be tough to open after a few years in a pickup truck or cement mixer anyway. Good luck!

    73, Rich

  6. #6
    August Johnson No Longer Registered

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    Got it open, couple hits with a rubber mallet loosened the base. Missing the channel elements. Now to look through my pile of manuals and elements and see what I've got. I'm familiar with these old units, converted bunch of old railroad MICOR radios to 145.01 for packet back in the mid 1980's. Got a whole bunch then for $10 each. Crystals cost more than the radio. Also used MOCOM 70's. I really like the bullet-proof front ends on these old rigs.

    August

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    I like the idea of using this too, and still use a lot of old stuff, but the limiting factor will be the crystal cost. I know it's heresy but I just buy the crystals and put them into elements myself, and honestly haven't had any issues doing it even though this no longer meets commercial specs. International is getting about $ 30 per crystal these days. You will probably have to do some hardware mods and do something about the helical resonators in the front end module (the cover comes off easily.) You will probably need to figure out how to get each resonator lower in frequency than the stock tuning will allow. Hopefully you have a test set because you will need it. These use a terrific amount of current on transmit in the power level this one is.

    I have been having issues with receiver Permakay filters lately. With no signal to the receiver, Meter 2 should idle at around 10-20 microamps. A zero reading usually means the Permakay has an internal failure. Then you need a scrap set for parts.

    Permakay filters had a lifetime warranty but that was then and this is now. I was getting warranty replacements on HT200 filters as late as 1980 but evem that was 36 years ago. The JC Penney car battery of the 1970's had a lifetime warranty as well but good luck getting one of those either.

    I have done a few rigs like this for hard core police car restorations where everything had to be right, and it winds up being expensive but has a high cool factor.

    PL reeds are available on eBay or via a want on the classifieds here or at the Batlabs forums classifieds.

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    I will be selling my entire collection (hundreds) of vibrasenders and vibrasponders as well as all other reed or card type filters I have for old gear around in one batch this summer. In a separate list I will move out what I have in channel elements also. Those will be listed on this site. I am not restoring any more old iron. More power to you guys, and keep the rubber mallets handy!
    Apparently NOT a radio professional.

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    Possibly some folks are having a senior moment here.... the Motrac did not use "channel elements", or, more correctly temperature controlled crystal oscillator modules (TCXO)'s. They used crystal ovens. The crystals were meant to be changed by simply plugging in a new one and putting the cover back on (it had screws to secure the cover). If you order xtals be sure to specify that they are for oven application for high temperatures. Many hams back in "the day" simply accepted some frequency drift and dispensed with the oven on VHF which typically operated on fundamental X 12. UHF was not such a good idea, operating at fundamental X 36. If anyone needs ovens for Motracs I have a box full someplace in the basement. Actually $30 for a crystal doesn't sound so bad, I paid that much for Micor crystals that were installed in TCXO's by the crystal company (International) and then they would do a temperature compensation run on the assembly and change the padding capacitor to the correct temperature coefficient to make the assembly meet stability specs. But of course everything is relative, you can buy a new Chinese radio for $39......

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    That is true, however the final generation of Motrac did indeed use channel elements rather than ovens. I am looking at one right now as I type this, a U73MHT-1100 high band mobile from 1968. Also, all the UHF MST series Motracs used channel elements, I have one of those here as well. Motorola discontinued the use of ovens in about 1967 and the Motrac continued in production through about 1972.

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    Well, like I said - some folks are having a senior moment here - and I am one of them. But I have a good (I think anyway) excuse - having built a crystal set in Cub Scouts over 60 years ago, and now working on APX's, my head is cluttered with too much stuff. You are correct, I was working for /\/\ C & E in 1971 and remember burning my fingers on those little gold boxes many times before the equipment in use began to become mainly TCXO types.

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    It was really kind of a mess at the end of Motrac production because they were changing styles of elements frequently. - - there was that silver two-piece element where the crystal was in the top section and the oscillator in the bottom, as the early Mocom 70's used, then there was that large (and rare) fat element that held two channels at once, in the satin blue colored housing, and then finally the TLN1081 and 1083 style elements that continued into the Micor era. The used two-way dealers would always rob the elements from the radios if the previous user hadn't done so already, along with the PL reeds, and then try to sell them back to you at high prices, and it was a hassle trying to figure out what # element you needed.

    I just bought a set of low band crystals for a military version GE Progress Line vibrator supply mobile that a friend wants on 51.0 in a restored Korean War era mobile airport control tower communications trailer. International's price was $ 65 to my door for two HC-6/U crystals. If you gotta have them, you gotta have them, I suppose.

    Off topic, but my Motorola SA-200 HF SSB pack radio uses two ovens for the crystals. Dates from 1966. I wonder why they didn't use a TCXO instead, and competitors used no compensation at all. Thing is, who would design a battery operated portable radio that used a set of ovens, to drain the battery even faster? Whoever designed this radio did...

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    On the subject of the manual for your Motrac - look on the chassis of the radio someplace. Motorola used to stamp the chassis with the 68Pxxxxxxx number, which was the part number of the manual that covered this particular radio. Our County shop had purchased 115 of these radios, back in 1975, just at the end of Motrac production. Our Motracs were hybrid in nature - all solid state except the final stage, which was a ceramic tube on UHF frequencies. We used the 4657 tube in these radios, but then changed to the RCA 8072 version tube for the final. When they would die, a slight tap to the PA section would cause the tube to arc - you could hear the switching supply responding to the bad tube right away. About 60 watts out with these mobiles.
    Oh those were the days. We were in tall cotton as it were - four channels - three being for use with a repeater, the fourth channel as a car to car. They had a little plunger that detuned the PA assembly 5 Mhz for car to car operation on the 453 Mhz band. What was cool about the receiver, is that it had AFC - it would tune the receiver to match what was heard. You used to have to short out the AFC line, to net the receive on frequency, then unshort the point on the chassis to resume AFC operation. I even aborted a receiver out of a mobile, making it operation all by itself. Fun times.
    MJ

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