Hello all,

I'm in the process of replacing an old (wasted) speaker
in a 1930's Superhet set. I will be installing a modern
Permanent magnet speaker. I understand that to minimize
hum, I need to install a resistor or filter choke. I prefer
to use a filter choke. My question is: how do I determine
the what size filter choke (henries, milliamps, ohms)
to use? The old field coil had a resistance of 1,060 ohms.
Thanks! Nik

: Hello all,

: I'm in the process of replacing an old (wasted) speaker
: in a 1930's Superhet set. I will be installing a modern
: Permanent magnet speaker. I understand that to minimize
: hum, I need to install a resistor or filter choke. I prefer
: to use a filter choke. My question is: how do I determine
: the what size filter choke (henries, milliamps, ohms)
: to use? The old field coil had a resistance of 1,060 ohms.
: Thanks! Nik

: Hello all,

: I'm in the process of replacing an old (wasted) speaker
: in a 1930's Superhet set. I will be installing a modern
: Permanent magnet speaker. I understand that to minimize
: hum, I need to install a resistor or filter choke. I prefer
: to use a filter choke. My question is: how do I determine
: the what size filter choke (henries, milliamps, ohms)
: to use? The old field coil had a resistance of 1,060 ohms.
: Thanks! Nik

Try this!

To replace the old speaker with a 4 or 8 ohm PM speaker will require installationn of an audio transformer to achieve maximum power output. The purpose of the XFMR is to match the relatively high impedance of the output of the power pentode with the low impedance value of the PM spkr. The pentode has an optimum desired load value usually identified as R(a). Typically in the range of 3000 to 5000 ohms.

To determine the turns ratio of the required XFMR use the following formulae:

N=(R(a)/R(spkr))^0.5, that is the square root of the turns ratio.

eg. R(a)=4000, R(spkr) = 4, N= 31.62.

That 's the theory, good luck!

: Hello all,

: I'm in the process of replacing an old (wasted) speaker
: in a 1930's Superhet set. I will be installing a modern
: Permanent magnet speaker. I understand that to minimize
: hum, I need to install a resistor or filter choke. I prefer
: to use a filter choke. My question is: how do I determine
: the what size filter choke (henries, milliamps, ohms)
: to use? The old field coil had a resistance of 1,060 ohms.
: Thanks! Nik

Are you really sure you want to replace it? Unless it is really
badly busted up, it's not too hard to rebuild it, preseving the
authenticity of the radio.

Assuming you decide to go ahead with the replacement:
I saw a good post on the topic the other day (probably on
rec.antiques.radio+phono newsgroup, though I can't find
it at the moment - anybody else see it?) I believe the
gentleman suggested using the primary of a 24-volt 2-amp
filament transformer in place of the old speaker's magnet
coil - the 24-volt leads are simply taped up and not used.
Bring the power up slowly with a Variac while you watch
the B+ voltage. Since the new transformer's winding has
less resistance than the 1060 ohms of the old speaker's
magnet coil, there will be less drop, and the B+ may rise
higher than you want. If so, you may need to add a series
resistor to limit it.

: Hello again,

Actually. the speaker will be "recycled" into an old
Silvertone deco stepped Tombstone that I own. It was missing
a speaker when I got it. So it worked out well. Don't worry,
I never throw out anything that's rebuildable...Nik

Caught a site the other day that may be of help if you
go the PM route. try www.tubesandmore.com/speaker01.html

Several more good hints on old sets as well.

I am in same sitution on old EM speaker but will have to
go PM since the old one is gone.