[Boatanchors] Headphone Impedance Matching

[D C _Mac_ Macdonald]

I think you can generally expect high impedance phones to work satisfactorily on low impedance outputs. 

The same is NOT true for low impedance phones on high impedance outputs.  The low impedance would seriously load down the output. 

* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk hotmail com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
* * * * * * * * * * * 
 
 
> From: macklinbob at gmail.com
> To: holden7471 at msn.com; dhallam at knology.net; Boatanchors at mailman.qth.net
> Date: Wed, 4 Dec 2013 10:18:30 -0800
> Subject: Re: [Boatanchors] Headphone Impedance Matching
> 
> I just looked at the schematic for the 75S1. It is designed for HI-Z 
> headphones!
> 
> Bob Macklin
> K5MYJ
> Seattle, Wa.
> "Real Radios Glow In The Dark"
> ----- Original Message ----- 
> From: "Howard Holden" <holden7471 at msn.com>
> To: <dhallam at knology.net>; <Boatanchors at mailman.qth.net>
> Sent: Wednesday, December 04, 2013 10:08 AM
> Subject: Re: [Boatanchors] Headphone Impedance Matching
> 
> 
> > They will probably work but volume will be low. The 600 ohm transformer 
> > will help decidedly until you can find a better transformer. You can also 
> > try using a 120V to 6V filament transformer. I've done that with an 8 ohm 
> > speaker on an early HRO and it works fine.
> >
> > Not sure how the headphone jack is set up on the 73S3, but if there's a 
> > series limiting resistor in there it may make things a little tougher. If 
> > there's one there you could temporarily jumper around it, but then don't 
> > plug in a regular 8 ohm set until you remove it.
> >
> > Howie WB2AWQ
> >
> >
> >
> > -----Original Message----- 
> > From: David C. Hallam
> > Sent: Wednesday, December 04, 2013 9:33 AM
> > To: Boatanchors at mailman.qth.net
> > Subject: [Boatanchors] Headphone Impedance Matching
> >
> > I picked up a Lincoln headset/boom mike set a few days ago. The box is
> > marked Telex but there is a Lincoln sticker and part number on one end
> > of the box. I found this set listed in a 1968 Allied Radio catalog with
> > the specs. The microphone is a high impedance ceramic element and the
> > headphones are 2000 ohm impedance. The high impedance microphone is OK,
> > but what would be the best way to match the 2000 ohm to my 75S-3, or do
> > I even have to worry about it? I have some 8 to 600 ohm matching
> > transformers, but nothing to match to 2000 ohm.
> >
> > David
> > KW4DH
> >
> > -- 
> > "I predict future happiness for Americans if they can prevent the 
> > government from wasting the labors of the people under the pretense of 
> > taking care of them."
> > Thomas Jefferson