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

[Michael (Mickey) Sattler]

Help please.

On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

To that end I believe what I need to do is get some U-94A/U plugs (with
built-in PTT) and the appropriate adapter (i.e. the Kenwood E11-0420-15
mic jack), figure out which wire is which, and solder away. I don't
believe that I need any capacitor with the PTT switch, but if you know
better I'd love to hear all about it.

I'm having trouble sourcing the U-94A/U, so I'd like some help on that
too.

Many thanks from all of you,

Mickey

 

[john smith]

Help please.
On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

To that end I believe what I need to do is get some U-94A/U plugs (with
built-in PTT) and the appropriate adapter (i.e. the Kenwood E11-0420-15
mic jack), figure out which wire is which, and solder away. I don't
believe that I need any capacitor with the PTT switch, but if you know
better I'd love to hear all about it.
I'm having trouble sourcing the U-94A/U, so I'd like some help on that
too.
Many thanks from all of you,

Do military headsets still have higher impedance than civilian?

 

[Dr. Anton T. Squeegee]

[email protected] (known to some as Michael (Mickey) Sattler)
scribed...

Help please.

On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

<snippety>

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.

 

[Fred McKenzie]

On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

To that end I believe what I need to do is get some U-94A/U plugs (with
built-in PTT) and the appropriate adapter (i.e. the Kenwood E11-0420-15
mic jack), figure out which wire is which, and solder away. I don't
believe that I need any capacitor with the PTT switch, but if you know
better I'd love to hear all about it.

I'm having trouble sourcing the U-94A/U, so I'd like some help on that
too.

Mickey-

Check out the Astrocom website at
http://www.astrocom-electronics.com/

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

 

[Don Byrer]

On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

Ditto the previous comment on impedance mismatch. Ham/LMR HTs are
8-16 ohm speaker impedance, vs typical 600 for aviation headsets.

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...<smack-smack-smack-smack...>"

 

[Casey Wilson]

Ditto the previous comment on impedance mismatch. Ham/LMR HTs are
8-16 ohm speaker impedance, vs typical 600 for aviation headsets.

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.

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.

 

[KENG]

Help please.

On behalf of a non-profit public service group I'm trying to adapt
military surplus Astrocom helicopter headsets to civilian uses, to be
used by ham radio users with Kenwood and Motorola handheld
transceivers.

To that end I believe what I need to do is get some U-94A/U plugs (with
built-in PTT) and the appropriate adapter (i.e. the Kenwood E11-0420-15
mic jack), figure out which wire is which, and solder away. I don't
believe that I need any capacitor with the PTT switch, but if you know
better I'd love to hear all about it.

I'm having trouble sourcing the U-94A/U, so I'd like some help on that
too.

Many thanks from all of you,

Mickey

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

 

[KENG]

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
http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-8416/dtl8416.pdf

KenG

 

[Ken Gremillion]

Mickey,
As a followup to this post, the adapter/transformer is MX-1646/AIC.
Link To Specs
http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-8416/dtl8416.pdf

One for sale here...
http://www.bpbsurplus.com/lc/cart.php?target=product&product_id=16496&category_id=296

 

[KENG]

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
Mickey,
As a followup to this post, the adapter/transformer is MX-1646/AIC.
Link To Specs
http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-8416/dtl8416.pdf

Here's one for sale:
http://www.bpbsurplus.com/lc/cart.php?target=product&product_id=16496&category_id=296
KenG