Re: [IRCA] matching transformers for old tube radios

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> I have a bunch of old antique and near-antique tube radios that I would
> like to hook up to my outdoor antennas.  What impedance should I assume
> for the antenna terminals so I can build matching/isolating transformers
> to attach to me coax lead-ins? I know it will probably vary with the
> radio, but what is a good ballpark impedance value to work with?

Most were set to work with a long wire or multi-turn untuned loop, so I'd
guess 450 ohms (9:1) would work well.  That would be my starting place...

Be careful if you use a separate speaker.  Some of the old radios used a
coil and steel core for the speaker magnet which doubled as the choke in the
power supply.  These can usually be recognized by a four-pin speaker
connection.

I haven't worked with one of these for many years.  They always were fun.
When I was a kid I fixed a 1940-vintage receiver.  I turned it on and my
mother happened to be in the room.  When it came on, Franklin Roosevelt was
heard giving a speech.  It was in the late 50's and some station was
rebraodcasting it for some reason.  It certainly freaked out my mother when
she looked at the radio and heard that!  Couldn't have planned a better joke
if I'd tried.

Craig Healy
Providence, RI

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