[R-390] EXT: Fwd: 600 ohm audio
Fisch, Michael
mfisch at kent.edu
Mon Feb 21 17:17:29 EST 2022
That is a good price. Several suppliers have the Bogen T725 transformer for when Jim runs out.
Mike
-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Jim Whartenby via R-390
Sent: Monday, February 21, 2022 4:56 PM
To: r-390 at mailman.qth.net
Subject: EXT: [R-390] Fwd: 600 ohm audio
Don't know why I have formatting issues with this reflector, geez! 2nd try:
If anyone is having trouble finding audio line transformers, I have two dozen NOS boxed transformers available.
Rated for both 25 and 70 volt lines at 10 watts, the primary winding has 8 taps and the secondary is set for an 8 ohm speaker.
Will transform the following impedances, as printed on the box:62.5 / 125 / 250 / 500 / 1000 / 2000 / 4000 / 5000 /
$7.50 each plus shipping from 71901
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
-----Original Message-----
From: Thomas Chirhart <k4ncgva at gmail.com>
To: Tom Frobase <tfrobase at gmail.com>
Cc: R390A <r-390 at mailman.qth.net>; Tisha Hayes <tisha.hayes at gmail.com>
Sent: Sat, Feb 19, 2022 4:05 pm
Subject: Re: [R-390] 600 ohm audio
I have a few of these:
A-8102’s
A-8103’s
24572 70.7v voice coils..
73 Tom K4NCG
Sent from my iPhone
> On Feb 19, 2022, at 11:17 AM, Tom Frobase <tfrobase at gmail.com> wrote:
>
> Just as a follow up, I needed a transformer for a unit I recently
> sold. I have a box of 25v transformers which were popular before 70v
> audio distribution. I found the 1 watt tap was exactly 600 ohms into
> an 8 ohm load. They should be very common on EBAY. … Tom, N3LLL
>
>> On Sat, Feb 19, 2022 at 9:43 AM Tisha Hayes <tisha.hayes at gmail.com> wrote:
>>
>> (Sigh) late to the conversation but I have a few things to add;
>>
>> If you are going to browse through ebay for 600 ohm to 8 ohm
>> transformers they can be a little pricey; People who have them know
>> that they are sort-of-rare and charge accordingly. But... people who
>> are selling off the old 70 volt field coil transformers do not know
>> the other uses for the transformer as an impedance converter from 600
>> to 8 ohms; You can get those pretty cheaply.
>>
>> If you look at old speakers there were quite a few that were
>> originally designed for 600 ohm sources. Some of the Hallicrafters
>> speakers supported a 600 ohm input and if you took the speaker apart
>> you would find a little transformer in there.
>>
>> You can also get transformers that are multi-tap and that allows you
>> to match up to 4 ohm speakers as well. Just checking quickly I see
>> that radiodaze has the 119DA that would allow you to connect up a 4
>> or 8 ohm speaker just by using a different tap.
>>
>> Another alternative would be to make your own little audio amplifier
>> that can take in a high-impedance input (600 ohms, whatever) and
>> drive an output to 4 or 8 ohms. You could even do it with an op-amp
>> or a simple transistor based amplifier because those devices don't
>> really care about the input impedance that much and are capable of
>> driving low impedance outputs (just not at a very high level), so it
>> would be good for low impedance headphones or ear-buds.
>>
>> If you want, you can even find 600 ohm headphones, but nowadays those
>> are usually high-end studio headphones. I have the Sennheiser HD600
>> that I do use for radio listening but mostly I use them for high
>> fidelity music listening. Those are pricey ($300 headphones) and
>> might cost more than your radio. Another place I have found impedance
>> adapters are the ones used for David-Clark aviation (pilots) headsets.
>>
>> Another route I took was to get a Bogen distribution amplifier; This
>> is a monsterous, 50 watt audio amplifier that you would use for a
>> building and had a 600 ohm input that could drive a variety of output
>> impedances. If I ever have a south american dictator surrounded in an
>> embassy and I want to drive them crazy/ out of the embassy I would
>> use that to play Barney the Purple Dinosaur songs non-stop for a few
>> weeks. (or anything from Nickelback).
>>
>> *Ms. Tisha Hayes*
>>
>> *AA4HA*
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