04-16-2014, 02:26 PM
I agree with Arron in asking what happened to your original speaker?
In post #4 you spoke of hum and seemed to imply swapping to a PM speaker will cure it. It will not.
The cap / choke (Field coil) / cap is a pie filter (as in the Greek letter as it looks like it).
A resistor is a poor substitute for an inductor in a pie filter. Your output voltage will be higher without the L unless you up the R and that will cause wider voltage variations with load - volume. You will have more hum without the L all else equal.
If you are fishing for a hum solution, replacing the speaker will make it worse not better. Jacking up the caps will help or totally mask the real problem.
As Morzh pointed out watch the cap size you are asking the 80 to operate into. No use to stress the old bottle.
EDIT: Just noticed from your schematic the original speaker VC is 89 Ohms probably 11:1 to your PM speaker. Therefore the transformed impedance to the plate of the 42 is about 1/10 of design.
In post #4 you spoke of hum and seemed to imply swapping to a PM speaker will cure it. It will not.
The cap / choke (Field coil) / cap is a pie filter (as in the Greek letter as it looks like it).
A resistor is a poor substitute for an inductor in a pie filter. Your output voltage will be higher without the L unless you up the R and that will cause wider voltage variations with load - volume. You will have more hum without the L all else equal.
If you are fishing for a hum solution, replacing the speaker will make it worse not better. Jacking up the caps will help or totally mask the real problem.
As Morzh pointed out watch the cap size you are asking the 80 to operate into. No use to stress the old bottle.
EDIT: Just noticed from your schematic the original speaker VC is 89 Ohms probably 11:1 to your PM speaker. Therefore the transformed impedance to the plate of the 42 is about 1/10 of design.
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