[Boatanchors] Patterson Power Supply Help Needed

[Ray, W4BYG]

I would suggest you look around for an inexpensive, maybe free, 5 watt PA
systems 70.7 volt audio transformer.  These are typically used to provide a
selected amounts of power to speakers in a distributed PA speaker system.
It is an auto-transformer with taps and should work well in place of the
original field transformer.  

They usually come with several impedance/power taps in that range, one of
which should work OK for you.  A similar 25 volt transformer with the right
taps on it would most likely serve as well.  

Anyone working in that field would likely have a good used one they would
give you.

I would think this would be vastly superior to a simple resistor.
Ray, W4BYG

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Joe Connor
Sent: Saturday, September 07, 2013 2:57 PM
To: boatanchors at mailman.qth.net
Subject: [Boatanchors] Patterson Power Supply Help Needed

I just picked up a nice Patterson PR-10 receiver but there is no speaker.
Originally, it had an electrodynamic speaker and a field coil. The schematic
is here: 

http://www.nostalgiaair.org/PagesByModel/091/M0013091.pdf

I want to substitute a PM speaker because I don't have much choice. The
schematic lists the field coil at 1.5K ohms. My plan is to change the filter
caps and substitute a 3K/10W resistor for the field coil just to see if the
receiver works. Does the sound reasonable? The two original filter caps are
8 mfd. Should I up the second one to 22 mfd for better filtering now that
there is no field coil or am I better off adding a second 3K/10W resistor
and a third 10 mfd filter cap?

I've read about these types of substitutions but have never had to do one.

Thank you for your help.

Joe Connor
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