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Marti Crystals

Posted: Wed Aug 28, 2019 6:05 pm
by radiowave911
We just came into posession of two Marti RPU transmitters that we would like to be able to use. We still occasionally use one for sports, and have a church that uses one on our frequency to send us their Sunday worship services.

Where would I go about finding crystals for these and is there any information out there on how to realign them once the crystals are changed? The models are RPT-15 and RPT-30. I pulled the existing crystals form the 15, and it looks like they are on-frequency instead of something that is multiplied to get to the frequency.

We are looking for crystals for 450.550 and 455.550.

Any suggestions on who might sell these and where I might find the necessary information to retune them? Even better is to find someone that can do it for us. RF is the area that I am shakiest in, unfortunately.

Re: Marti Crystals

Posted: Wed Aug 28, 2019 6:40 pm
by rfn
I just had two RPT-2s overhauled by BE (successor toi Marti). Had been told to expect a long turnaround but they were back amazingly quickly.

I had suspected crystals but the problem turned out to be the crystal ovens, Right now I'm looking at two RPT-15s which seem OK on frequency - they were seldom used - however every capacitor in them is pretty well dried out. Usage is so small that there's little incentive to spend even $5 on repair. Of course if you're looking to change frequency that's a whole different can of worms. I'm about 900 miles away from the transmitters just now but vaguely remember the original manual having a rather complete retuning/aligning procedure described. If you don't have the books they may be available online.

Re: Marti Crystals

Posted: Thu Aug 29, 2019 8:11 am
by Dale H. Cook
rfn wrote:
Wed Aug 28, 2019 6:40 pm
... vaguely remember the original manual having a rather complete retuning/aligning procedure described.
I think that is the case, though I have not changed frequencies on an RPT-15 or RPT-30 in about 25 years. IIRC you will need a deviation meter or service monitor to set the deviation.

Re: Marti Crystals

Posted: Thu Aug 29, 2019 3:51 pm
by TPT
Bohn Broadcast ( also services the older crystal controlled Marti equipment.

If you register on the BE site, I believe they still have the older Marti manuals available as a PDF.

Re: Marti Crystals

Posted: Fri Aug 30, 2019 6:24 am
by kcbooboo
The biggest hurdle will be getting new crystals. International Crystal Mfg closed. Bomar isn't really an option. Your best bet would be to send the oscillator schematic and maybe even an old crystal to QuartsLab over in England.

I've worked on a couple of Marti units. They're no harder to work on than a crystal-controlled two-way FM radio. There are heaters for the crystals, multiplier stages, front ends, IF stages, discriminators, power amplifiers, etc. Similar test equipment will work with the Martis. One big difference is that the Marti units are designed for continuous transmission, unlike mobile radios.

Bob M.

Re: Marti Crystals

Posted: Fri Aug 30, 2019 7:12 am
by jammerdave
Maybe just try BE? Awhile back, I called them for some 950 STL rocks, and they had them in stock. Maybe they might for RPU also?

Re: Marti Crystals

Posted: Wed Sep 04, 2019 3:53 pm
by radiowave911
Thanks, all. We have contacted Bohn. Hopefully, they will be able to change the frequency. I no longer have access to the test equipment I used to, and being a High School station we do not have the budget for it (the hardware was all the right price - free). If we can get these usable for us for a reasonable price, then we will put them in service. If not, they will likely be recycled.