Wanted: Info on I believe MOCOM

[jmr3865]

Ok, MY Fire Company recently retired our 1968 Mack that was refurbed in 82. We are trying to restore it to somewhat original. Anyway, Within this transition, our radio was moved to another vehicle. From what We can gather, We may have had a 1 ch VHF HI MOCOM 70. It didn't scan, Im not even sure if it had a pl. I am looking to narrow down the model we actually had. Does anybody have any info on the mocom series so I can narrow down? If I can, I want to try and get one, I'd LOVE to get a working one and to get it to our freq. I might be able to get a picture of it installed, I'll see what I can do.

[PETNRDX]

The Mocom 70 used a control head that was the same casting as the Motrac.
Painted tan color, round green "power" lamp on one side, red "Tx" light on the other, the lamps were in the upper corners of the head, squelch and volume knobs were below the lamps.
Some models had PL toggle switches, some a toggle switch for F1 / F1, most had the rotary.
They came in one to four channels, with the most common ones I have seen ( used ) were the four channel.
They were also used with the "Systems 90" push button head like a Micor, but that was less common.
They did have a scan head that attached to the bottom of the older Motrac style head, but they were not very common.

[jmr3865]

AHA! So I need a MOCOM 70 single channel with PL on 158.775 pl 151.4! Wonderful, thanks!

[PETNRDX]

And for if some reason you can't find a Mocom 70 chassis, you can use any of the older Motorolas, and just use a Mocom head.
So, for example, you really could use a Motrac, Mocom, Mitrec, or Micor since the radio chassis might be "hidden" behind or under a seat.
But, I suppose there are enuf old Mocom 70's around you can likely find one and the channel elements.

[Andy Brinkley]

IIRC the older Macks were all positive ground, and some I worked on were 24V and you had to pull the power for the radio from between the 2 batteries. (24 V / 2 = 12 V)

You might want to verify everything before connecting the radio, or you else you will let a lot of the test smoke out from inside the radio.

[PETNRDX]

That is a good point.
That age of truck is just old enuf to be from those Pos ground and 24 v days.
It may even have had a "Twin V" radio...

[WB6NVH]

Just to clarify, there was a scan accessory adapter which bolted to the TOP of the Mocom-70 head, not below it. A single amber lamp, toggle switch an 4-pos. priority switch. The Mocom 70 did not come with a plastic Systems 90 head, although later on some were adapted to work with them and sold as a replacement accessory.

Certain Motracs were capable of positive or negative ground, there is a polarity plug inside, and I think the cable had to be changed as well. The 24 Volt trucks require that you tap from one battery.

Mocom 70's are almost give-aways on eBay, but it will take awhile to find a high band one. Remember that they are not type accepted nor capable of proper narrow band operation, which is scheduled to be mandatory soon.

In 1968 it would not be likely to find a Mocom 70 in service. I believe they were not introduced until after 1970, hence the name. In fact, it's not well known that Motorola first called the Mocom 70 the Motran II and then apparently changed their mind. The State of California bought a quantity of Motran II's, that's the only place I have seen any.

A typical 1968 installation would have been a Motrac or a 15" T-Power drawer such as the T53GKT series. Maybe even an older Twin-V.

[PETNRDX]

Thats right.
I remember now.
I am pretty sure I have one of the scan heads out in my old parts stuff.
I used one on VHF some years ago.
As I recall, jumpers set the scan list, and the selector on some versions set the priority.
Others were an "all or nothing" scan.
I had mine set up for scan of only the "selected" channel, and the one priority.
Been a long time.

[Will]

I have the book on the Mocom 70 and the Scan head (Motrac vintage). I may have a Mocom 70 head in my collection.

The Mitrek will work with the Mocom 70 control head, cable, speaker and microphone, with one minor wiring change. The Mocom 70, late Motrac, and Motran have the positive ground adapter jack in them. Mitreks go Positive ground with a change in the control cable, and a minor change in the Mortac/Mocom 70 control head.

In 1970-74 I had a T Power in my Toyota Land Cruiser, T41GGT3100

[tgo]

My company fleet was almost exclusively Mack and used MoCom-70's. Positive ground was standard on Mack vehicles until about 1976 but the earlier ones were 12/24v and later ones were straight 12v. If you have the 12v/24v setup there will be a series-parallel switch and related wiring under the passenger seat. This enabled 24v to the starter during cranking but standard 12v hardware (lamps. etc.) for everything else.
Our MoCom-70's had the optional polarity converter plug inside the transceiver unit. To convert to negative ground for other brand trucks, pull out and reverse position. It's described in the MoCom-70 service manual.
Because of the low typical annual mileage of our trucks, we kept them a long time. When it came time to replace the MoCom-70's and Mitreks with MaxTracs, we converted the remaining trucks to negative ground.

[Glen W Christen]

The Mocom 70 came out in late 1969, using the identical head for the MOTRAC. The initial run was low band, then VHF, which used the same exiter and PA with a varactor tripler to provide a 30 watt UHF transmitter. Later models used the same chassis with a MICOR PA deck to give a 75 w UHF, 100 W VHF, and 110 W low band.

The Micor was also introduced in late 1969 in low band. The first one that we installed came back the next day, complaining that they couldn't hear more than one or two words: with the engine running it was putting out 150W and the temperature sense circuit was shutting it down (an all-or-nothing in low band).

The first MOTRAC was the T51HHT model, (low band, 1958 or 1959) full tube transmitter, solid-state receiver, with exceptional sensitivity. They were +/-, 12/24, plug-determined, initially limited to 2 frequencies. They did expand the line to 4 frequency but that required a second oscillator chassis which added about 4 inches to the length of the radio. The crystals were in heated ovens until later in the run when Motorola switched to channel elements at the same time that they went to a solid-state exciter (LHT) and could accomidate 4 frequencies in the standard chassis.

The line continued through the MHT model using tubes, then transitioned to the low-power MOTRAN but I don't remember the model #. (MST?) There was a very limited number of UHF Motran which used a high-frequency tube but didn't last long because the Mocom 70 replaced it with a fully transistorized PA.

[jmr3865]

Does anybody know where I can find a MOCOM 70 single channel with PL on 158.775 pl 151.4 at?

[WB6DGN]

...then transitioned to the low-power MOTRAN but I don't remember the model #. (MST?)

My Motrans are U51LLT and U43LLT. These are the first ones they made. The U51 is a 50watt, 40 - 50 Mc split and the U43 is a 30watt. The VHF high is basically the 50watt low band transmitter with a varactor in the output circuit for operation on 150Mc.

Does anybody know where I can find a MOCOM 70 single channel with PL on 158.775 pl 151.4 at?

The likelihood of finding a radio on the channel you need is pretty small, much less with the proper PL. You'll need to find a suitable redio, preferably in working order, then go to someone like International Crystal or Bomar for the crystals. As for the PL reeds, I don't know of anyone who still makes those; you'll probably have to try to find those used, online. I have seen them listed occasionally but finding the proper frequency might involve a bit of searching. I'm looking for some for my Motran too, though, right now, not too aggressively. Good Luck,

Tom DGN

[jmr3865]

Just for :o's and giggles, here is a picture of it in the truck!

http://www.facebook.com/album.php?aid=1 ... =507381186


And no, that is not me!!!!

[fineshot1]

Just for 's and giggles, here is a picture of it in the truck!

http://www.facebook.com/album.php?aid=1 ... =507381186


And no, that is not me!!!!

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