Boat Anchor (Motran) Assistance

[WB6DGN]

I have a VHF Motran (U43LLT-3100A) that I would like to retune to a 2m ham frequency. Receiver is no problem as that receiver was also used in the conventional Motrac models and is pretty straightforward. My question is regarding the transmitter alignment, specifically the tripler/output stages. Does anyone have a manual on this radio that, (a.) they would be willing to sell, or, (b.) failing that, that they would be willing to scan the transmitter alignment page/s and email (or snailmail) them to me. As I recall, the alignment of those stages was pretty persnickety and the varactors would show their displeasure with misalignment by letting their smoke go free. In this day and age, that would pretty much relegate the radio to doorstop duty. Any and all help from you old-timers would be much appreciated.
Thanks,
Tom

[WA2VNV]

Are you sure those are Varactors or just the the old stud mounted transistors in the final area? The Motran I have has transistors and there is a doubler-driver in the final compartment that takes the 75 Mhz from the exciter bd and doubles it to 150 MHz and it is then amplified and sent to the 3 paralleled final transistors to generate ~40 Watts output. Does this sound/look like the same unit?

George

[WB6DGN]

I wish it was just a transistor, then I wouldn't have to handle it with kid gloves (at least as much). No, Motorola, always trying to be at the forefront of technology, chose to use, essentially, the 50 Mc., 50 watt exciter and a varactor tripler to come up with about 30 watts on 150 Mc. In that day and age, high frequency, high power transistors were few and far between and, I don't think there was even anything available in that power range; at a reasonable cost, at least. I've never looked at one of these radios on a spectrum analyzer (I probably wouldn't like what I saw); they were far too costly for the average shop at the time. There was talk of using the same approach on UHF a few years later but, as far as I know, it never happened. All of the power transistors in this thing, whether RF or power control are TO-3 cases; not conducive to low input capacitance! I'd sure like to get this thing up and running, as far as I know, this is truly the FIRST all solid state radio commonly available for land mobile radio. By the way, another interesting innovation for the time; the antenna switch was also solid state, NOT PIN diodes, but Schottky diodes, if I remember correctly, that used 105 volt forward bias to switch the signal, so a high voltage supply (T-power) was still required, though no where near as high voltage or current (but you still hear the whine on transmit!). Thanks for the reply, hoping someone kept that old paperwork.
Tom

[WB6DGN]

The Motran I have has transistors and there is a doubler-driver in the final compartment that takes the 75 Mhz from the exciter bd and doubles it to 150 MHz and it is then amplified and sent to the 3 paralleled final transistors to generate ~40 Watts output.

That sounds like a much later design than what I have. Mine is an "L" transmitter and an "L" receiver, thus the U43"LLT". I'm guessing yours is a higner letter. This, no doubt, reflects Motorola's disenchantment with the performance of the varactor scheme, either reliability or spectral purity (or both). There sure is a lot of stuff around that I've never heard of before; I wish someone would write a detailed chronology of Motorola products if it hasn't already been done. Thanks again for the reply.
Tom

[k2hz]

You are correct that the "LLT" was basically a low band exciter driving a varactor tripler. I looked through my old manuals and all I can find is the later "M" series that was a true high band exciter that did not have the varactor.

What is the model number of the exciter/multiplier board? Maybe I can find something that way.

I do recall that the LLTs were touchy to tune.

[WB6DGN]

What is the model number of the exciter/multiplier board? Maybe I can find something that way

Hi Richard, thanks for the reply. I found a few numbers but the ones that, I think, would really be useful are not visible without extensive disassembly, if then. The entire transmitter/power supply number is TUD1152AB-1. The exciter board and low level stages is a TLD8542A. Unfortunately, the number for the higher level stages is not to be found. The output filter is TLD6552A and the varactor reference designation is CR110 but no other information is visible on that section. I did very carefully diddle with it on the commercial frequency it originally was on (153 Mc) and everything tuned rather smoothly UNTIL I got to the varactor stages. There seemed to be no rhyme or reason to that and I quickly got scared off before I damaged it. Strangely, I didn't see a low power "TUNE" switch. I sure would have felt better if I could have reduced the power while messing around. After being sure that it still worked OK, I packed it away until I find the instructions.
Tom

[WA2VNV]

Tom,
I looked at the manual I have and it is for the newer Motran series U43MST-3100, dated 4/5/1973. I modified/reworked this mobile drawer for full duplex Tx/Rx repeater operation and it is still in use today after 32+ years continuous operation on the local 146.760 repeater. Back then, (1976) I only needed ~10-15 Watts output to drive the infamous AM-494/GR "Green Monster" military 1/4 kW amplifier (made by Motorola) running a pair of 4CX250B's. (Upgraded from the orig 4X150 glass tubes).

The original Motran doubler/driver/final configuration was terribly inefficent and generated too much power & heat for use as an repeater exciter. So I designed & built up on a PC board, a 2 transistor circuit that took the ~250 mW drive @73 Mhz, doubled it with a 2N5589 to ~3 Watts at 146 MHz, and then drove a 2N5590 for a final output of 10-12 Watts. This board was installed into the final compartment space to utilize the heat sink and shielding after the orig components were removed. 2 newer transistors replaced the 6 stud mounted older types of the orig configuration.

Good luck with your conversion project. The Motran "L" series receiver is only surpassed by the newer Micor series, for a non synthesized receiver. However, the Motran transmitter is another story, You may consider doing something like I did if you think it's worth you time. Much better solutions are possible today. YMMV.

George

[WB6NVH]

They must have made at least three variations of the VHF Motran, because the book I have is for a U43MSN, still not what you need, and I thought I had everything! I think these radios were rather rare because of the price, so they and the manuals were probably scarce.

[Will]

Yes, basically there were three versions. The U43LLT in two versions, and the U43MSN.
The LLT had the LHT receiver, the varactor tripler/transmitter, and the switching power supply to run the 50 mhz power amplifier stage.
The MSN had the later M receiver and an all 12 volt transmitter/power amplifier stage at 30 + watts.

I worked on hundreds of these in the 70's.

The U43LLT radio has basically the same transmitter power amplifier as the U51LLT.

[WB6DGN]

George, I enjoyed reading about your project; in earlier years that's what I enjoyed doing as well. Had dozens of mods. for the old Link gear including a 5894 conversion for the 829B that they used in their high power VHF transmitter (the old 2-piece radio). Yes, getting rid of that varactor would be the smart thing to do if I wanted a radio to use in everyday service. Nowadays, though, I'm more interested in restoring the radio to it's original condition. I think the "nostalgia" bug has bitten! Sort of like "restoring" the old Model T instead of putting a "muscle car" engine in it and hot rodding it! I think it has something to do with ... AGE (?)!!! By the way, I fully agree with your opinion of the Motrac/Micor receivers. I, for one, have not seen anything available anywhere that can outperform them and most fall far short of their capabilities, especially selectivity. There's no doubt, those big, heavy preselectors were put there for a good reason!

Will, I wonder if your memories of those Motrans would enable you to, sort of, talk me through the alignment of the varactor section of my high band radio? If you didn't want to take up the space here, I could send you my email address to go direct. I have two of those radios, a 40 - 50 Mc that I plan on converting to 6m ham, front end willing, and the 150 Mc that is the subject of my post. In both cases, the 50 Mc. transmitter tunes smoothly and intuitively (and I have the manual for the 50 Mc. radio) but I just don't know what I'm doing with the varactor tuning on the 150 radio and I'm scared to venture too far with it as I'm concerned about destroying the varactor without some direction to go by. I do have a Motorola test set so meter selection and readings should correspond to Motorola's figures pretty close, anyway.

Thanks again to everyone for the replies. Even if I haven't, as yet, gotten the information I need, it has been fun hearing from those that still remember, and use, those great old radios.

Tom

[WB6DGN]

I still need help aligning the varactor output stages of my Motran transmitter. If anyone has a manual OR the experience to "talk me through" the procedure, I would sure appreciate the help. THANKS,
Tom

[WB6NVH]

I can't help you with the high band version, but the low band will require some mods to make it to 52.525. The transmitter requires a capacitor change on the exciter board and the receiver requires that the capacitors on the oscillator-multiplier board be changed to lower values. If you weren't aware of this already, send me a PM and I will forward the procedure on to you. The front end is hard to align from a "cold start" and you usually have to inject a signal about halfway through the inductor chain to have it hear it at all, and then back your way out to the antenna connector.

[WB6NVH]

Tom, you apparently have PM replies blocked in your profile so that I can not reply to your PM (although I can read it.)

Just send me an e-mail using the e-mail button below and give me your standard e-mail address in that message. I will get the low band Motran conversion instructions to you that way.

The receiver front end tunes at least to 52.800 without changes, I never tried it higher. There are two different front ends, one with the delay line for "Extender" operation and the other, a simpler one, for non-Extender operation. Most buyers, paying the premium price for a Motran in the first place, knew enough to buy the receiver with an Extender, so most have them.