for the old timers club...

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Mar 24, 2002 12:03 am

My local 2-way shop was nice enough to give away a dead 2-channel 90-watt VHF-Hi Motrac to me (humm.. gee thanks?)

Anyway, I found out how heavy these darn things are, since I never dealt with one in person before. I mean, I have only seen them on TV in Adam-12.

I really liked the cloth-coated wire. Was PVC invented yet?

It's nice to know I have an antique in my possession. You know, Motrac was the first mobile radio that didn't require the engine to be running to be used.

Being as vaccum tubes are not very common today, I really don't want to bother tracking down replacement tubes.

So, what older Motorola radios use tubes?
I'm a less concerned about final PA tubes.

I know Motrac is loaded with tubes.
I think I heard Micor has a tube or two.

Anyway, I'm scared of tubes, and want to avoid them (no offence.)

Any suggestions.

_________________
Jonathan KC8RYW
I'm voting Green in 2004! <a href="http://www.takethepledge.com/">www.take ... /a>

[ This Message was edited by: KC8RYW on 2002-03-24 21:08 ]

EC-7 · Post by **EC-7** » Sun Mar 24, 2002 12:30 am

The Mocom 70 UHF used a tube on the output final stage.
If you can find the tube #'s you need, I can contact my friend who has a TON of radio tubes(over 10,000). I'll bet that he has what you need. FYI, He lives in Brighton.

Jim202 · Post by **Jim202** » Sun Mar 24, 2002 9:42 am

The Motrac was a nice radio in those days. There were 2 flavors of it. The early version had all tubes in the TX. The newer version had only 3 tubes if my memory is correct. The PA, the PA driver and a pre driver. The rest was all solid state.

Think I still have a couple of them in the garage. They were capable of 4 frequencies if all the parts were installed. Had a few special models that did even more.

Jim

jim · Post by **jim** » Sun Mar 24, 2002 12:55 pm

Are any of those sitting in your garage 33ish lowbanders?

KG4RZU · Post by **KG4RZU** » Sun Mar 24, 2002 3:05 pm

The 60,90,110 Watt Motracs used a 8552 tube for the doubler-driver, and a 8643 for the power amplifier. I have a set if you need them. Motracs were a very tough radio, and still are. I used one until recently going to a Maratrac for more channels. I still use one in my wife's van. Hope they didn't take the channel elements, they're out there,but hard to find. I have a few VHF elements w/heaters also, and a small selection of PL reeds.

Jim202 · Post by **Jim202** » Sun Mar 24, 2002 3:17 pm

No such luck, they are both in the high 42 - 50 split.

Jim

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Mar 24, 2002 5:33 pm

<img src="http://personal.cmich.edu/~weirm1js/Mot ... ac_top.jpg" alt="MoTrac">

[ This Message was edited by: KC8RYW on 2002-03-24 21:33 ]

Tron · Post by **Tron** » Sun Mar 24, 2002 5:38 pm

Why are you scared of tubes?

Tron

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Mar 24, 2002 6:03 pm

Oops. The rig did come with tubes. I just had to be smarter then the radio, and check under the rear part of the heatsink. There was the doubler and the PA tube.

<hr>
Why am I afraid of tubes?

In a simple answer: Lack of experence.

_________________
Jonathan KC8RYW
I'm voting Green in 2004! <a href="http://www.takethepledge.com/">www.take ... /a>

[ This Message was edited by: KC8RYW on 2002-03-24 21:11 ]

KG4RZU · Post by **KG4RZU** » Sun Mar 24, 2002 7:04 pm

No need to be scared of tubes.. Even though they draw more current at times than transistors or IC's, they are far more forgiving with power surges and glitches. I have some that have survived lightning strikes that have taken out major appliances in my home.. I have 5 or 6 Motracs and GE Master II's standing by for backups in case of major lightning storms in the foothills of Carolina's that might take out some IC's in my base.. Motracs are easy to tune also...

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Sun Mar 24, 2002 7:42 pm

Another question...
Is the Motrac key universal? Do they work on all Motracs, or did Motorola try to issue the radios keyed diffrently?

Elroy Jetson · Post by **Elroy Jetson** » Sun Mar 24, 2002 8:51 pm

Some Motracs use 5984 output tubes...in fact, every high power VHF one I ever opened had that output tube type.

No mobile mount Micor EVER had a tube in it. Only the high power Micor base stations and repeaters had a tube, and that was a ceramic final for the high power units.

When working on a Motrac, use GREAT CARE because the plate voltage can KILL YOU if you get across it. They ran up to 1200 volts!

Earlier Motracs had a lot of tubes in them. The later ones only had tubes in the output stage.

A good Motrac, properly tuned and in good working order, offers SUPERB performance.
Its technical peformance in both transmit and receive is SUBSTANTIALLY better than any newer product in most respects. Selectivity is outstanding, and spectral purity of the output is outstanding as well. But they're definitely not a broad banded product. I think they can't spread more than 1.5 MHz (VHF versions) from the highest to lowest channels without degradation.

Quite a few Motracs are still in service and putting out a great signal, particularly in repeater operation. They get a new driver and a new final tube once in a blue moon and otherwise are happy to be ignored by the serviceman and just used.

You can get fantastic tube life out of one by turning the output power down some. As a general rule, detuning the output power by ten percent doubles tube life, and at half power you'll get ten times the rated tube life, or more.

They're old, and they're technically obsolete, but they're great old radios and if one will work for you for a specific application and it's in good shape, there's no reason to dump it until it eventually fails...and until then, it will perform at LEAST as well as ANY newer radio.

Elroy

EC-7 · Post by **EC-7** » Sun Mar 24, 2002 9:07 pm

Is the Motrac the same exact thing as the Mocom70? That pic looks just like my Uhf Mocom70 radios inside.

As far as I know, M only has 2 keys, the popular "Chicago Lock 2135" and another one for newer repeaters. I always have the main key with me, you never know when youll need it, and it comes in real handy at radio swaps

techie · Post by **techie** » Sun Mar 24, 2002 10:29 pm

I know of at least 4 common motorola keys:

2135 - mobiles (CG1 blank, same cuts as MOT1)

2553 - some base stations

MOT1 - older convertacoms (same cuts as 2135, CG5 blank)

unknown - small tubular type key for some newer convertacoms (mt2000)

there are several other types:

2007 - Nucleus paging cabinet
2141 - IMTS control heads

see http://www.repeater-builder.com/rbtip/motorolakeys.html

Jim202 · Post by **Jim202** » Mon Mar 25, 2002 6:03 am

There are a few other keys.

CH751

CH545

2252

Jim

Jonathan KC8RYW · Post by **Jonathan KC8RYW** » Mon Mar 25, 2002 11:31 am

Great, thanks for the info.
_________________
Jonathan KC8RYW
I'm voting Green in 2004! <a href="http://www.takethepledge.com/">www.take ... /a>

[ This Message was edited by: KC8RYW on 2002-03-25 14:45 ]

Hartley · Post by **Hartley** » Mon Mar 25, 2002 12:53 pm

Hi EC-7,

The Motran looks a lot like the Motrac (which is what's in the picture) - but the Mocom 70 looks a LOT different! Green colored case, almost twice as thick, with heat sinks on the back only (not on the side). I've never heard of a MOCOM 70 with a tube in it, but I suppose it's possible. The boards & parts are VERY different from Motrac/Motran
I have a MOCOM 70 carcass around here somewhere, I'll see if I can take a picture of it.

Hartley

[ This Message was edited by: Hartley on 2002-03-25 15:55 ]

techie · Post by **techie** » Tue Mar 26, 2002 12:18 am

see http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 1715471335

scroll down towards the bottom, and there is a photo of a mocom70.. not the best view, but it's the only one i could find on ebay tonite

Ohh.. better yet.. see: http://www.tapr.org/tapr/pdf/mocom.70.uhf.pdf
some good views of both interior and exterior..

Glen W Christen · Post by **Glen W Christen** » Tue Mar 26, 2002 1:11 pm

The Motrac had a lot of variations. Dual receiver radios were at least two feet long with second front end squeezed into the frame. Early models had plug-selectable 6/12 v pos/neg ground, and some were 12/24v pos/neg ground.
Railroad Motracs were 72v/12v but were not immune to vibration-I repaired many that came in litterly held together only by the wiring harness. These had ten power transistors in a series/parallel combination, depending on the voltage applied, and when one went you might as well replace all ten.
Early Motracs came out in the mid/late 1950's and used all tubes in the exciter with heated crystals in both Tx & Rx. Solid state receiver was a major advance.
Another variation was the Business Dispatcher, a low power unit. The early versions used the receiver from the very early motorcycle radio, then migrated to the same preselector as the Motrac. I gave last rites to one a year ago that was built in 1961 because the 'magic light bulbs' finally burned out.
The Motrac was virturally indistructable and when it did fail it was repairable.
The Mocom 70 ABSOLUTELY never used tubes. It and the Micor were the first high power solid state mobiles and both came out in late 1969.

Glen W Christen · Post by **Glen W Christen** » Tue Mar 26, 2002 1:45 pm

More info: The first models were the HHT, A version and progressed to the E version. All used a tube exciter but the board changed from point-to-point wiring to printed circuit traces. The receiver also made the same transistions but in different configurations.
PL reeds started out the old copper-cased ones and progressed to the small reeds used through the MICOR line.
Reverse-burst on TX was accomplished by using a slow-release mechanical relay.
After the HHT the went to the LHT (Low band, if I remember correctly) and the MHT (high band. The repeater was MSY. The MOTRAN was MSN but was a very short production run because it was replace by the Micor and Mocom 70.
Low band Motracs were extremely selective on RX - unless it was a very small shift you had to take the top cover off and inject a high-level signal one stage at a time to get any signal through to the receiver. Once you got your course tuning close enough to open the receiver then you could fine tune it down to around .04uv. The only front end I saw badly damaged was when a power company truck hit a 13,000 volt line with his whip. Instant smoke.