Hi all ...I have a Model V Simplex radio (schematic is on this site) I have electronicaly restored the radio. Problem= my volume control has tested fine with meter ..but, I get volume only when it is turned up 3/4 of the way..full volume...and nothing below that. I took the control apart...have black resistance strip that checks out good with meter...put back together and tests good with meter but same problem mentioned above when operating in radio circut.....HELP.....

Here is the schematic (the bottom one on the page): http://www.nostalgiaair.org/PagesByModel/446/M0018446.pdf

I believe that this is a design problem. The volume control circuit is rather unorthodox and it's no wonder it works poorly.

Essentially, the 100K pot is between the cathode of the first RF amp (the 44) and ground. Weird.

Maybe you could try substituting an audio-taper pot and see if that helps. But my sense is that without making some significant design changes, you'll have to live with it.

Maybe somebody else will see something I don't?
Doug

:Hi all ...I have a Model V Simplex radio (schematic is on this site) I have electronicaly restored the radio. Problem= my volume control has tested fine with meter ..but, I get volume only when it is turned up 3/4 of the way..full volume...and nothing below that. I took the control apart...have black resistance strip that checks out good with meter...put back together and tests good with meter but same problem mentioned above when operating in radio circut.....HELP.....

Is the volume control one of those Centralab-style pots, about 2" in diameter, with graphite on a paper substrate? Have you verified that it's 100K by measurement?
Doug

:Hi all ...I have a Model V Simplex radio (schematic is on this site) I have electronicaly restored the radio. Problem= my volume control has tested fine with meter ..but, I get volume only when it is turned up 3/4 of the way..full volume...and nothing below that. I took the control apart...have black resistance strip that checks out good with meter...put back together and tests good with meter but same problem mentioned above when operating in radio circut.....HELP.....

Has the 0.1 uF cap across the volume pot been replaced with a good equivalent cap??

THANKS TO BOTH YOUR ANSWERS To answer both questions....yes it has that paper/graphite substrate i check it it works well..just not in radio...also yes new cap has been put in ...I BELIEVE IT IS A DESIGN FAULT because the volume will come up slowly just ..only in the last 3/4 of control though....cheap thing

:Has the 0.1 uF cap across the volume pot been replaced with a good equivalent cap??

GB,
You could try altering the net R with powdered graphite. I created an entirely new graphite rheostat volume control for an Edison 7R. Worked great considering the complexity of this unique (dual) counter-rotating element.

marv

:THANKS TO BOTH YOUR ANSWERS To answer both questions....yes it has that paper/graphite substrate i check it it works well..just not in radio...also yes new cap has been put in ...I BELIEVE IT IS A DESIGN FAULT because the volume will come up slowly just ..only in the last 3/4 of control though....cheap thing
:
::Has the 0.1 uF cap across the volume pot been replaced with a good equivalent cap??

I have no experience with this type of volume control ckt - but I think it's a poor design. The pot is essentially just a cathode resistor (with cap bypass) in the first RF stage.

However, I'm surprised that the pot is 100K. I might try one with a smaller value.
Doug