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philco 80 jr. help please. 1st time restoring a radio this old
#36

thanks again Jerry.

yes, as far as i understand it, these "regen" type radios take full advantage of the "flywheel effect".

the volume control had me completely stumped before i figured out that it was actually an RF gain control.
Gary from PTOTP clued me in by telling me that the volume pot was a linear taper when i was sure it would be audio taper.

Ok, first the good news. I am pulling in stations!!!!!!!

they actually sound pretty good even if they are on top of the hum.

i am embarrassed to say that i think the reason i didnt notice them before is that i didnt let the set warm up enough before i tuned around the dial. Icon_redface (typical solid state guy)

now, on to the hum issue. i will take you guys through the steps i did and let you tell me what you think.

first, i pulled the 2nd oscillator tube. the hum disappeared!

then i put the 2nd oscillator tube back in and removed the detector oscillator tube.
the hum was still there.

next i put the tube that was in the detector oscillator location, into the 2nd detector location.
hum was still there.

this says to me that the hum is coming from the 2nd oscillator section, and its not the tube itself.

i had read that the 1 meg ohm resistor in this section should be mounted as far from the #14 coil as possible, so i added some wire to one end and moved it away a bit.
no change. hum still there. (not sure if this had anything to do with the hum, but it was worth a shot!)

next i began poking around with my trusty chopstick that i use for all high voltage situations, and couldnt make any change in the hum

finally, i grabbed the wire going to the control grid (top) of the 2nd oscillator tube, and the hum got much louder.
i had previously removed this coil in order to change the 50pF cap and to do Ron's 4meg to 2meg mod. i also replaced the wire going to the grid cap.

this makes me wonder if i somehow changed some parameter of the 2nd oscillator circuit by doing this change. obviously the size of the new components is not exactly the same as the old ones.

i stopped there since it was very late and i hadnt actually made the radio worse.
(always a good place to stop!)

so thats my progress so far.
ill hold off on removing the #14 coil until i hear back from the group.

thanks again for the help,
LC


Messages In This Thread
RE: philco 80 jr. help please. 1st time restoring a radio this old - by loosecannon - 09-06-2014, 07:32 PM



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