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 Post subject: Brandes headphones
PostPosted: Jan Fri 19, 2018 1:18 am 
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Joined: Jul Sat 30, 2016 2:37 pm
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Rookie. I have a pair of brandes headphones how do I go about adapting of regular rca plug to it the headphones have 3 wires coming off of them I want to plug them into.my shortwave radio. Thank u Jim


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 Post subject: Re: Brandes headphones
PostPosted: Jan Fri 19, 2018 2:06 am 
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Joined: Jul Tue 21, 2009 1:38 pm
Posts: 920
Location: SW WA state
Greetings,

First thing is to determine if these are high impedance (600, 1000, 2000 Ohm or some other high value) or low impedance (maybe 8-30 Ohms) headphones.
What is the output impedance of your receiver?
Let's assume that the Brandes are high impedance (1000 Ohms), and your receiver is 8 Ohms... Guess what! You need to match the impedance if you want good audio volume...
So, You may need an audio transformer.
Check your headphones: With three wires, one may be a common, the other two hot.
You will probably wind up paralleling them to reduce impedance if that's the case.
Best of Luck!

-Tom


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 Post subject: Re: Brandes headphones
PostPosted: Jan Sat 20, 2018 1:57 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 7861
Location: Ohio 45177
I have several pairs of Brandes. They are high impedance. I don't see a disaster drivig phones with a low Z source. Just that it won't be that efficient so maybe not play as loud as a better match is all. As I recall, they have the elements wired in parallel not in series so if one goes out the other side can still work. As for having three wires, I cannot figure that out unless you have one common wire and one for each side. As they normally terminate in two tip pins for connection. There should be two screw terminal jacks on each side of these. Are you saying the original wiring is damaged or missing?


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 Post subject: Re: Brandes headphones
PostPosted: Jan Sat 20, 2018 2:39 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
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Other than a definite lack of comfort over extended periods of time the vintage Brandes headphones should work OK with a low impedance output and most sets have enough audio reserve to drive them. Although high impedance they are low enough to protect the audio output transformer which can build up very high voltage across an unloaded secondary. The Brandes phones have a wonderful vintage look but I have never cared for them and the only set I use them with is a Heathkit crystal radio.

You often run into a problem using modern high sensitivity low impedance phones with a vintage receiver in that they will have a very loud fixed hum level. The best headphones I have found for vintage receivers have:
1. Comfortable fit
2. Selectable stereo/mono switch (unless they are native mono phones which are fine).
3. Individual volume control (controls if stereo), this allows you to dial in a little attenuation to make the hum go away

It is important never to have a receiver operating into no audio load since this can damage the audio output transformer. If in doubt about your headphones or wiring do NOT run the volume up hoping sound will suddenly appear because you may be destroying your output transformer and you will see many receivers have a high value resistor in parallel with the headphone jack to provide protection if there is an issue with the circuit; others also use a resistor to attenuate the headphone output.

Some receivers, like the SX-42, have a safety cage around the audio output terminals to protect the user from shock hazards due to the high audio voltage that can be developed across the set's 500 ohm output terminals. Too bad Hallicrafters wasn't as concerned about safety with their HT-19 transmitter which cosmetically matches the SX-42. I have one and the plate and screen supplies for the 4-65A final are brought out to two pairs of open binding posts on the back panel so that an external modulator can be used to provide high level AM transmission with this CW/NBFM transmitter. The plate terminals have around 1,500 volts on them, I added a plexiglas safety cover over mine.

Rodger WQ9E


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 Post subject: Re: Brandes headphones
PostPosted: Jan Sat 20, 2018 3:41 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1271
Location: Santa Rosa, CA
If the output of your SW receiver is 8 ohms or in that ball park
the correct way to drive high impedance headphones, which your
Brandes are, is to use a matching transformer. An audio output transformer
from a small tube radio will work fine. This will maintain the proper
impedance to keep your SW radio happy and provide plenty of
volume in your 'phones.
Steve

_________________
'cell phones and the internet are tools, not a lifestyle'


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 Post subject: Re: Brandes headphones
PostPosted: Jan Sun 21, 2018 1:22 am 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 3045
Location: Tucson, Arizona U.S.A.
Quote:
the headphones have 3 wires coming off of them

A photo would be helpful.

Are there really three wires? Could it be that there are two wires and a non-electrical extension of the outer jacket which can be attached to something for strain relief?

Also, ARF frowns on having two threads on the same subject.

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Jim Mueller


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 Post subject: Re: Brandes headphones
PostPosted: Jan Mon 22, 2018 1:44 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 7861
Location: Ohio 45177
For some reason I thought of solid state low Z output which does not really care, but I can see where some tube sets might like a load if nothing is built in like an attenuator for headphones that provides a nominal load along with reducing output to phones level.


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 Post subject: Re: Brandes headphones
PostPosted: Jan Mon 22, 2018 3:46 am 
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Joined: Apr Sat 11, 2015 5:30 pm
Posts: 625
Location: West Point, PA
I think the short answer is "don't waste your time." or "no, you can't easily do it."
That being said, just do it and see if it works!


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