[R-390] 600 ohm audio

[Tom Frobase]

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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