Motrac D73MHT-3100-A mobil question

[firedog359]

Hello everyone, I'm sorry to keep pestering everyone but I don't have anyone else to ask. I bought a Motrac mobile and a couple of control heads off ebay. I have another post asking for info on the heads. now I need help with the mobile. According to the model number breakdown, this is a VHF highband radio with 5 kHz channel spacing. It is set up for 151.955. Which tells me this is a business band radio. I did not know this until I actually received the radio and was able to look at the components. I am a firefighter and all of the radios in my collection are 155.415 which is my county fire dispatch channel. Can this radio be changed to that frequency and if so, with it being 5 kHz narrowband, can I transmit on it?

[kb4mdz]

1) Yes, it can be changed in frequency. You'll have to get a new Transmit crystal and a new Receiver crystal.

2) A leeeetle more complicated. Legally, no. And its "5KHZ Narrowband" is compared to the older "15 KHz wideband"; whence the transition from 15 KHz to 5 Khz was a long time ago. A very long time ago. If the serial number is still on it, look at http://www.akardam.net/moto/tools/serial4.pl will tell you its age, tho year codes might be stamped on components inside.

Museum piece, as far as a commercial/fire radio.

[Bill_G]

No. It cannot be narrowbanded to modern standards. And though technically it could be re-rocked to your favorite channel, finding a vendor could be difficult.

[firedog359]

Thanks for the replies, As far as it being a museum piece, I bought it as a collectors item anyway. I just want to change it over to my fire freq. to match the rest of my pieces and I was hoping that maybe I might be able to TX on it.

[Bill_G]

Well, you'll have to go in search of a company to make the crystals. Then you get to find someone with experience with the model to install the rocks, and tune it up. A four meg move will require a tune up. And then there's the issue of whether it will work or not. The final tube might be dead, or the t-supply high voltage section could be dead. And there could be a whole host of problems with dried caps that aren't caps anymore. You found a chicken coop car, and as dreamy as it might seem, the interior is rotted, there's some rust, and it definitely need tires. OTOH, it is a hobby.

[SteveC0625]

You may find that the receiver needs a bunch of parts swapped just to make it work at the different frequency. It might be easier to find the right frequency receiver to drop into it. In the 1970's we had a new 2 channel Motrac that received on 158 and 155, and it needed two separate receivers in the case to work properly. The chassis was nearly two feet long. Radios were much different back then than they are now. That beast was a 100 watter, and the headlights on our dual battery 1971 Cadi ambulance would dim when transmitting with the emergency lights going.

[firedog359]

Just a follow up, I have managed to find a control cable and I also purchases a Motorola TU546P test set at the Hamfest in Shelby, NC over the weekend. kb4mdz-The serial number is still on it but a little difficult to read. it is DE776Z. The chart shows this as a March 1979 build. That's ironic for me. That's the year I graduated from community college and started getting interested in electronics. My next goal is to find the proper manuals and a microphone. Thanks.

[Astro Spectra]

Good luck with your exxon project!

[abbylind]

Hey remember Permakay filters have a lifetime warrantee......

[Bill_G]

The Permakay will have clear date code on it that he could read to determine the week and year this radio was built. MHT's were some of the later versions. It might be as new as 1973.

[firedog359]

I found a component marked Permakay with a part # 68P81041A25 but the other numbers and letters are pretty much unreadable. What numbers/ letters should I look for to determine the date code? Also, I checked the serial number (DE7767) against the serial number charts and it shows this to be a 1979 unit. I didn't think these were made that late.

[firedog359]

Just a note, the serial number that I am referring to is the actual radio serial number and not something on the Permakay.

[Bill_G]

Look for four digit numbers printed on just about any part that are by themselves. That will be the week/year that part was made. Since you have a clue about the production date, you're looking for number that end in 78 and 79. You may also find a fully printed date inside the chassis from a rubber stamp, though it may be hidden behind a board, or large part.

[firedog359]

I found another couple of number strings down on the side of the Permakay. one reads TFN6017CS and right below that is stamped 327924. With the 79 being in that string, I think that might be the date stamp but I'm not sure. I guess I'm still confused about the build date. I did not think that the Motrac was being produced this late in the 70's.

[Bill_G]

Find a transistor. You'll see the type like 2N9543, and below that will be four digits usually in lighter color ink.

Or find an electrolytic cap (aluminum tube). You'll see the value (1uF for example), and a big part number, and four digits by themselves.

[firedog359]

I'm still looking for those numbers but now I have another issue. I know that there are supposed to be tubes under the back heat sink. I pulled the heatsink/ cover off and there is one tube on one side and what appears to be a large white tube socket on the other side with an aluminum cover sleeve and two rubber pieces on copper straps. Is there supposed to be some type of tube there? also, there is a black plastic spacer between the existing tube and the metal plate that its socket is mounted on and that spacer is broken in half. When I pulled the heatsink off, two small looped springs fell out. any guidance on these issues would be greatly appreciated. Thanks.

[Bill_G]

Yeah. Not surprising that a tube is gone. They are becoming really hard to find. I'm not surprised about the broken insulator either. Between age, and being cooked to death during it's life, it was bound to deteriorate. This is becoming more and more a real chicken coop car. I hope you didn't spend too much. Since you don't have any experience with the model, no manuals, and are missing pieces, you have a real project. You won't get this running any time soon. My advise is to box it up, and lug it down to a hamfest sometime to see if anyone is interested in what you have. Sorry. It might have some sentimental value to the right guy.

[impalass427]

I have many old service manuals and found a similar chassis used in a base station. The 2 tubes shown in the schematic are 7551 ans 8552, so see if the one thats there is one of these two, then you will know which is missing.