[Hallicrafters] S-2OR speaker change over ? issues !

[Rodney Bunt]

Kim,

I am at present reading a good book from the 50's called "Elements of Radio Servicing" got it from
ABE books on line (second hand of course) they discuss doing such a replacement.

There are a couple of issues here.

1) The field coil is used to "smooth" the High voltage. You can replace this function by using a
choke of apropriate value OR a resistor to get the required output volts and smoothing. The field
coil is a 1.4kOhm type 53-V-27

2) The S20R uses a HUM BUCKING speaker, the voice coil (the one that moves) is wired in series
with another coil which is stationary and coupled to the field coil, this has induced in it a
current "opposite" to any hum that is coming from the high voltage current going through the field
coil this also "bucks" any HUM from the audio stages. (NOTE: if you install a new speaker and the
hum is excessive reverse the voice coil wires ( this puts the hum bucking coil in correct phase,
as you cant reverse the hum bucking coil as one leg is earthed)

So if you overcome the high voltage power supply ripple/voltage issues, be aware that there will
be considerable HUM in the audio. You may need to increase the value of the HV ripple/filter
capacitors, and this will invariably increase the high voltage, so you will have to insert a
resistor inbetween the 80 rectifier and the first filter cap, this will aid smoothing also and
reduce HUM.

It all depends upon how much trouble you want to go to....

I hope this has been helpful.

Rodney
VK2KTZ

--- Kim Roland <KROL at triad.rr.com> wrote:
> Hi, I am new to restoreing these Hallicrafter radios. I know there are people out there with
> electrical knowledge & support only if someone takes time to respond. What is purpose of this
> site to me as a new hobby to restore these     Hallicrafters radios if no one cares to be of
> assistance? I had posted an earlier question on (S-20R schematic question) Only one person 
> responded, but he had no schematic. Roy-thanks for your time.I did a search on archive for this
> question but found no response. Has anyone replaced the field coil speaker of S-20R with a PM
> speaker.If so, can anyone provide any information ? Thanks    
> 
> 
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