Adapting Astrocom headset - need U-94A/U plug and a little help

In article , snipped-for-privacy@gmail.com (known to some as Michael (Mickey) Sattler) scribed...

Obtaining the connectors and 'soldering away' may be the least of your worries. You could easily be dealing with differences in impedance for both mic and earpieces, and in how the microphone circuits do their thing.

Aircraft radios are almost universally designed to use a carbon- button microphone (or the electronic equivalent thereof). This means that they all provide DC bias on the mic circuit. Whatever radio you end up adapting the headset to will also have to provide this bias if you want the mic circuit to work right.

As for the earpieces: Typical impedance for aircraft-type headsets is 150 ohms. You will need some sort of impedance matching for optimal performance.

What you will need is the schematic of the headsets, AND the schematics of the specific radios you intend to use them with. You will need to do some careful study to insure compatibility. If there are issues such as mic bias, you will need to design your adapter to take that into account.

Happy tweaking.

Mickey-

Check out the Astrocom website at

They have a downloadable catalog, but it is 23 MB. You might send them an eMail explaining your project, and ask for technical information about your particular headsets.

If the headsets can be used, you may want to just wire new connectors on them, and not worry about adapters. The U-94 connectors might cost more than you think!

Fred

Ditto the previous comment on impedance mismatch. Ham/LMR HTs are

I played with an old British aviation headset once, setting it up for a Yaesu ham HT...the audio was useable but very tinny driving 600 ohms directly. Would have been better with a 600-8 ohm transformer. The mic element audio was way too low to be useable and I ended up strapping an electret element to the original mic...worked OK, but of course it was no longer noise cancelling and was way too sensitive.

However, yours being old military heli sets, they may be lower impedance.(?) First of all I would try ONE headset with the speaker & mic audios mocked up to the right connectors for the HTs. I would plan on cutting off the existing heli plug and wiring thru a tiny box to hold a PTT switch, and any matching network you may need.

Or...sell the headsets on ebay and buy what you really need...!

--Don Don Byrer Radar Tech & Smilin' Commercial Pilot Guy Amateur Radio KJ5KB kj5kb-at-hotmail.com

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..." "Watch out for those doves..."

Nope, 600-ohm was the standard when I was a radio operator for Uncle Sam's Misguided Children back in 195....., well, long enough for them to be considered "old" even if'n I'm not.

Mickey, Back in the olden days, I was a Comm Tech in the USAF. One of my accomplishments was designing a mod for C-12 aircraft (Civilian Beech Queen Air), which used the non-mil Headset/Microphones. The aircrews wanted to use H-157 Headset ($57.00, and available on every USAF base in the world) instead of special order David Clark Headsets at a cost of over $300.00 at that time. There is a audio transformer that was specified in one of the radio test sets to do just what you want. It even was pre-wired with a U-92/U on one end. You would need to add the connectors for H/S and Mic to the attached cable. The transformer is MX-!#^*%/ARC. This worked great for the crews, and I was awarded a substantial sum for the suggestion/proposal. The aircrews did not want/need the PTT feature you are wanting. I will search through my papers for the exact part number of the transformer. FYI, the transformer is housed in a cylindrical can about 1.5" by 4" with 2 cables attached, one cable has a U-92A/U attached, the other has no termination.

KenG

Mickey, As a followup to this post, the adapter/transformer is MX-1646/AIC. Link To Specs

KenG

Mickey Mickey, As a followup to this post, the adapter/transformer is MX-1646/AIC. Link To Specs

Here's one for sale:

Mickey, As a followup to this post, the adapter/transformer is MX-1646/AIC. Link To Specs

One for sale here...

KenG