Motorola / Bendix ADF-12 Valve-based ADF Unit

[saddlestone-man]

Not quite military, I assume this is from a civilian light aircraft, but maybe someone on the forum can help me? It says Motorola on the front panel, but I believe Motorola acquired Bendix, so this could be one of their models.

I've acquired a Motorola model ADF-12 valve-based ADF receiver, see photos. There are 4 valves in the unit (removed for the photos), and are: 12BA6 / ECC82 / 12BE6 / 12??6.

The back panel says 28V at 3.1Amps, and the model number says 2303DF.

I believe there was a later transistorised version of this ADF, the ADF-T-12, but mine is definitely valve-based.

Does anyone have any information and/or a schematic for this module. I'm wondering if it could be converted into a LW/MW tuner

best regards .. Stef

[turretslug]

I suppose you could say that it already is a rather nice MW/LW tuner... It ought to be as good as it (sensibly) gets for pulling in "the usuals", it is a shame that BBC WS 648kHz is no longer around, and I daresay a replacement loop could be made to increase its utility. I'm guessing that the four-gang tuning implies sub-190kHz IF, not to mention good front-end performance. I'd wondered if it it was one of those pieces of equipment designed to operate its valves from 28V nominal HT(in practice, 26-27V with generators turning), examples that spring to mind include the BC1206 and the R392. Hints against this are the presence of what appears to be a 250V electrolytic and the quoted 3.1A consumption- I'd expect consumption for a 28V HT circuit to be heaters + at most 50mA. A need for an external power pack would hardly be insurmountable, though. I wonder if there was an airframe-mounted power pack/interface unit.

I haven't looked particularly exhaustively but haven't spotted any germanium detection diodes, which makes me wonder about what goes in the IF valve socket- 12BA6 would be possible, so any diode(s) may be hiding. Hopefully, this doesn't mean that there's too much in an external box and that this is indeed capable of being a more-or-less self-contained tuner. The valve screening cans look to be a little unusual and as the valve types are exposed anode types (i.e. no overall internal mesh screen), they could well be important for circuit stability as well as retention in something with a biggish flat-four throbbing nearby. Ah, beg pardon, you mentioned removed for photos.

Interesting little unit.

[AC/HL]

It does look to be just the receiver front end. There will be an RF amplifier and the fourth capacitor section is for tuning the loop. As you say, the performance should be quite good on MW/LW as well as the aviation beacons.
There's not much use for ADF on the ground, but interesting nevertheless, and not very common.

[AlanC]

That could be an interesting project! A good receiver it will be, with all that front end selectivity and gain. I suspect it sends the IF signal out of the big Jones plug on the back, to another unit which will contain the demodulators and the drive electronics. How these generally work is that in ADF mode, the loop aerial is rotated by a servo motor that drives the loop toward the null condition. A synchro transmitter on the same shaft drives the indicator instrument on the pilots panel.

This link http://vk2bv.org/archive/museum/adf14.htm describes a very similar unit with a lot of layout similarities, it gives supply voltages etc. The block diagram shows how the whole thing hangs together; you have the radio receiver part.

You could just add a single IF stage and detector perhaps, there looks to be room in there!

Cheers,
Alan

[Radio Wrangler]

Bendix is owned by Honeywell.
Before that Bendix bought King who were one of the major radio manufacturers in the private aircraft market.

Stuff marked Bendix is most likely commercial or military... ditto Motorola

David

[saddlestone-man]

Thanks to all who have posted comments, it's much appreciated.

best regards .. Stef