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Author Topic: HELP NEEDED: Bendix TA-12D transmitter, MP-28 Modulator-Power Supply  (Read 7248 times)
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W2FBR
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« on: October 20, 2016, 05:13:35 PM »

I've recently purchased this transmitter off eBay and awaiting it's arrival. I need to know if someone can give me the frequency ranges of the four channels it is capable of operating on. I've had a couple of them over the years and this one is the "D" model. I'll pick up a copy of the manual eventually.

From looking at the photos, it needs an original replacement power plug. If anyone has a junker unit with this plug, I'd be interested in purchasing it. I have a poorly modified MP-28 modulator-power supply coming as well. I know I'll need a schematic for the MP-28 if it's not in the transmitter manual. I'll know more when these pieces finally arrive at my QTH.

Thanks,

Steve
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Steve Davis, W2FBR
Keansburg, New Jersey USA
Pete, WA2CWA
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« Reply #1 on: October 21, 2016, 02:31:15 AM »

According to the TA-12D manual:
Channel 1 - 1050 to 1700 KHz
Channel 2 - 2000 to 3400 KHz
Channel 3 - 3000 to 4800 KHz
Channel 4 - 4370 to 7000 KHz
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
W2FBR
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« Reply #2 on: October 21, 2016, 07:20:27 AM »

Thank you, Pete. It looks like it may be easy enough to move to 160 and 40 meters. Does the manual you have listed cover the MP-28 as well?
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Steve Davis, W2FBR
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« Reply #3 on: October 21, 2016, 02:27:10 PM »

No information on the MP-28 in the TA-12D manual.
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
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« Reply #4 on: October 22, 2016, 04:05:59 PM »

I think the only difference between suffix versions was the upper and lower channel frequency coverage. 

The MP-28 schematic is in the Surplus Radio Conversion Manual, Vol. 2, in the TA-12B conversion section.  The B & C version Bendix tech manual also covers the MP-28, at least the MP-28B version, with pracatical wiring diagrams and schematic.  I think the conversion manual book has been scanned and is on the web somewhere but the TA-12 manuals were not, at least in a usable form, the last time I checked.

As you may know, the MP-28 is the hardest component of this system to find and in recent years what examples have shown up on eBay have gone for astronomical prices.

I suppose you know you will need the accessory tune-up meter box with the cable and male plug, or a homebrew facsimile.  I think the control box may be needed too.

I am also working on a TA-12, I think it's also a "D," and will probably wind up making an AC power supply and modulator because I have no MP-28 at the moment.

Fair Radio Sales may have a scrap TA-12 to cannibalize the original male chassis connector from.   The cable side of the connector is available on eBay at the moment from a guy who seems to have a vast variety of semi-rare military WWII connectors, mostly new old stock. 

When I look at the cabinet and see that goofy hinged panel where the connector is located, I envision some engineer at the time saying "Boss, we have a problem, by putting the connector on the side we just found out we can't slide the transmitter into the case!" and the boss saying "Well, get the production guys to cut a flap in the case there and it will look like we knew what we were doing all along!"
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Geoff Fors
Monterey, California
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« Reply #5 on: October 22, 2016, 11:39:25 PM »

See attached


* TA-12-Modulator-Pwr_Spy.jpg (452.37 KB, 4500x3300 - viewed 1255 times.)
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
W2FBR
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« Reply #6 on: November 03, 2016, 02:27:10 AM »

Geoff and Pete,

Upon inspection of my newly arrived TA-12D, I've discovered that it's been rewired for 12 volts and channels 2, 3 and 4 have been modified to cover 80, 40 and 20 meters respectively. Since channel 1 is close to 160m, I may get ambitious and just modify that oscillator coil as well.  Thankfully, the large antenna relay was not removed, so that's a plus. It looks like I'm going to need a few more parts to make this transmitter right. In other words, a junker would be a handy thing to have right about now. At least the previous owner didn't make destructive modifications that couldn't be worked on and straightened out.

Geoff, maybe I will take your advice and call Fair Radio Sales and see what they have available. I did order two connectors from that fellow on eBay in anticipation of finding a chassis connector for the transmitter. My MP-28 still has it's original Cannon connector. I'm no stranger to this transmitter, this being the second one I've procured through the years. My first one was a G model.

Pete, I've ordered several manuals from your site, including two for this transmitter. Have you seen my order and payment for them via PayPal? I ordered them on October 26th. Please advise.

Thanks,

Steve, W2FBR
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Steve Davis, W2FBR
Keansburg, New Jersey USA
Pete, WA2CWA
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« Reply #7 on: November 03, 2016, 02:53:50 AM »

USPS says it will be there 11/3/16.
Track: 9505 5158 9296 6307 0117 34
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
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« Reply #8 on: November 12, 2016, 08:11:16 AM »

It looks like other forum members have covered you...I'm working on the TA-12C and have all of the blueprints.  As a previous poster mentioned the Surplus Conversion manuals are helpful.. Vols 1-3 can be found online.

If you need more docs, let me know.  12v rewire is common, and it's a pain, but check the resistors in the oscillator sections, the values in mine were sky-high.

If you need knobs, parts, I may still have a few.
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W2FBR
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« Reply #9 on: November 17, 2016, 05:22:07 PM »

It looks like other forum members have covered you...I'm working on the TA-12C and have all of the blueprints.  As a previous poster mentioned the Surplus Conversion manuals are helpful.. Vols 1-3 can be found online.

If you need more docs, let me know.  12v rewire is common, and it's a pain, but check the resistors in the oscillator sections, the values in mine were sky-high.

If you need knobs, parts, I may still have a few.


Thank you for the offer on the parts. The one thing I do need is the chassis mounted Cannon power connector for the transmitter. The oscillator coupling transformer out of a C-model's Channel 4 position would be a big help too. My D-model was rewired for 12V and had other modifications done to it, but nothing that would be too difficult to deal with. At least the transmitter wasn't hacked to bits, so that's a plus.

Steve
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Steve Davis, W2FBR
Keansburg, New Jersey USA
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