[Milsurplus] Receiver audio out Z (was Need 4000/4(or 8) ohm audio trans

[Jim Madden]

Good to know thanks. I thought i had read somewhere the hs-18 and 23 had used 2000 ohm ear pieces in series it's been a while since i last read it.Thanks for the correction.Jim 

 
 


From: WA5CAB at cs.com
Date: Tue, 8 Sep 2009 23:38:57 -0400
Subject: Re: [Milsurplus] Receiver audio out Z (was Need 4000/4(or 8) ohm audio trans
To: jrm1967 at hotmail.com

Jim,

The HS-18 and HS-23 are 8000 ohm.  They each use two R-14 receivers in series, each of which are 4000 ohms.

The HS-33 and HS-38 each use two 300 ohm ANB-H-1 receivers in series.  So they are as you say 600 ohm headsets.

However, they didn't come out in the late 30's.  The Navy used low-Z audio in both ground and aircraft sets from the 30's on.  But the Signal Corps (and the AAF/AAC) didn't begin serious changeover efforts until late 1941.  The first several Order runs of SCR-274-N were high-Z only.

The MC-385-(*) started out as the MC-385-A, not -C.  First order appears to date from August, 1941.  However, the power handling capability of the MC-385 is small.  It is not a suitable adaptor for an LS-3 tied to a BC-779 (which runs a pair of 6F6's in push-pull in the output).  However, it does work fine with any of the headsets.

In a message dated 9/8/2009 10:16:41 PM Central Daylight Time, jrm1967 at hotmail.com writes: 

Their is an adapter typically used on WWII aircraft but may have been used by the sig corps also.

    The hs-18 and hs-23 headsets were 4000 ohms and the change out to the hs-33 and hs-38 600ohm headphones was occurring in the late thirties. Since so many High z phones were out there and the cost of retrofitting existing radios was out of the question the MC-385-C and  D was developed to fill the gap. I just purchased one yesterday for 3 bucks at a fleamarket.to use with my urm-25F and  H-113/u headphones.
Regards, Jim Madden Ham call KB1PFL  


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