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Author Topic: OLD headphones, modern TXR  (Read 594 times)
AE4RV
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« on: April 22, 2004, 03:23:20 PM »

I would like to get some old, maybe WWII vintage, headphones for my Ham (mostly CW) operating.  Rigs are all fairly new (New Icoms, Elecraft K1).  

1 - What type/brand is best, and where to look?

2 - What kind of 'matching network' will I need since I understand the impedance of very old headphones is likely to be in the thousands.

Before anyone asks "why?" I'll go ahead and say: Because I want to.

Thanks! - Geoffrey, AE4RV
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WB6BYU
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« Reply #1 on: April 22, 2004, 03:46:44 PM »

Radio Shack carries (or at least used to...) an audio
transformer with a 8 ohm secondary and 1000 ohm CT
primary.  Connect the 8 ohm side to the rig and put
your high-impedance phones across the high impedance
side.

Actually, any tube-era speaker output transformer will
work the same way, and will probably be a higher
quality, lower loss, and a few pounds heavier.
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AC5E
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« Reply #2 on: April 22, 2004, 04:19:59 PM »

Geoff, I second Dale's motion to use a tube radio output transformer connected backward to drive a WWII vintage Brush, Roanwell, Telex, or what have you, headset.

I sometimes hook up my old Brush - or the equally old Roanwell - for a short run down nostalgia lane. But frankly, I can't stand those ear biters for more than a few minutes at a time. And never could.

Back when they were all you could get, we used to put dime store powder puffs between the hard plastic earpieces and our ears. That increases the comfort factor greatly - but they still hurt my jug handles after an hour or so. And when I swipe the wife's (that would be YF back when) "cootie dusters" she complains and I get powder in my ears.

The Sony's are much better.

73  Pete Allen AC5E
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K8AC
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« Reply #3 on: April 22, 2004, 04:41:48 PM »

Check with Fair Radio for the headphones.  My favorites were the military headsets that used the chamois covered earpads, which were the most comfortable headphones I've ever used.  We're not talking high-fidelity here, so no need to search out audio matching transformers.  Find a small filament transformer and use that for impedance matching if necessary.  You'll likely find that no matching is required with the high impedance phones.  
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K0IZ
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« Reply #4 on: April 22, 2004, 05:21:36 PM »

Telex made some nice earphones, can be found from time to time on eBay.  Usually you can hook a high impedance load (earphones) across a low impedance output (rig)and everything will work fine.  You won't damage anything.  However audio level might be lower than desired, in which case a matching transformer backwards (4 ohms to rig, 500 ohms or whatever to earphones) would solve that problem.

Low impedance across a high impedance output is not, however recommended without a matching transformer.
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AC5E
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« Reply #5 on: April 22, 2004, 06:19:12 PM »

For clarity - a transistorized audio amp that expects an 8 ohm load sees the 1 to 5000 ohm load of most of the 1940's era communications headsets as essentially an open circuit. Some audio output stages will work FB - and some will self destruct in short order.

And there's no way to tell what will happen unless you try it. Essentially, that is playing Russian Roulette with an expensive toy.

A couple of bucks for a stepup matching transformer is darn cheap rig insurance.

73 Pete Allen  AC5E
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W4TYU
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« Reply #6 on: April 22, 2004, 06:37:57 PM »

The WW2 headphones we used back then were the type with the thin metal diaphragm. Forget the military number.

But the best I had my hands on came from a WW2 Tank Radio Set made for either the British or for the Russians. They had a cloth strap over the head with the spring going behind the head.  The headphones were like little speakers with actual speaker cones in them.

Ole man JEAN  
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AE4RV
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« Reply #7 on: April 22, 2004, 09:24:52 PM »

Thanks to EVERYONE for the replies.  Great information, thanks again.

I have a pair Trimm Professional cans on the way and I will probably build a matching network of some sort.  I was getting comfortable with the idea of plugging them in to my rigs as-is but Pete has scared me!

73,
Geoff AE4RV
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WB6BYU
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« Reply #8 on: April 23, 2004, 03:10:40 PM »

Geoff -

If you want to plug them "as is", you can add a
shunt resistor in the plug as a load for the audio
amplifier stages.  Probably something between 10 and
100 ohms should do the job.  Some radios already have
a resistor wired across the headphone jack internally.
Check the schematic on your radio.

If you add it into the headphone plug, just remember
it is there in case you ever plug it into an old radio
designed for the high impedance phones!
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