I have restored a late 1930s Canadian Sparton AC radio which work fine but I notice very sharp static when tuning towards a station (580 kc) the low end of the dial. It is not noticable at the high end. Still have not replaced all capactors. Any advice?

Brian,
Check for debris or slightly malformed plates in the variable tuning cap. There could possibly be a short condition caused by either at one end of the dial.

Set the tuning cap to create maximum static noise then GENTLY prod the tuner plates with the eraser end of a pencil to see if the condition changes. If so, thorough cleaning between the plates (aluminum whiskers possibly) or a careful straightening of the plates would be in order.

Once you've either found the problem there or eliminated this possibility you can then move on to more serious troubleshooting if necessary.

Sharp crackling static can also be caused by silver mica migration in the IF transformer capacitors. This loud static would not be variable with the volume control but would most likely be present throughout the entire tuning range.

Agree with checking the tuning capacitor thoroughly - that's the likely culprit. I seriously doubt silver migration however since that bit of technology wasn't even available in the late 1930's when your radio was made. It is most often seen in later vintage sets mainly from the 1950's &60's.....

Thank you gentlemen, it was a slightly bent plate, (luckily on the outside) that needed a bit of strightening. Thanks again.

:Agree with checking the tuning capacitor thoroughly - that's the likely culprit. I seriously doubt silver migration however since that bit of technology wasn't even available in the late 1930's when your radio was made. It is most often seen in later vintage sets mainly from the 1950's &60's.....

Hi Brian and Dennis,
Your question and answer were appropriate here. I have an AM/FM where the AM was scratchy in the middle of the dial. Each end was fine, though.
It had the same problem. I could put an ohm meter across the plates and get intermittant shorts in the area of the scratchyness. It is the obvious cause.

On this radio there was a screw adjustment on the very back of the tuning condenser. Adjusting that cleared the problem. No bending of plates was necessary.

Best Regards,

Bill Grimm