Just finished recapping this model...which should've been a straight forward fairly easy restoration (I've done two 42-345's, and a 42-327 which are similar without problems). But it's been anything but. First the band switch was majorly corroded. I'd never seen one that bad before. I may have to just leave it on AM broadcast because it's so finicky. But that's not the main problem I'm having. I can't get anything on the dial below 1300. There is no discernable drop off point. Just hissing like it's trying to receive but can't quite do it. The local station at 1470 comes in loud and clear and a few others around it, but that's it. I tried swapping tubes one at a time to no avail. I traced the signal all the way through each tube plate and grid, so that part is good. So I'm looking for ideas. What would cause 3/4 of the dial to be dead? Could it be a mica cap? I didn't change those. The resistors all checked good, but could one that has drifted border line be a cause of this? I had a couple of radios in the past that a tube was the culprit of the missing part of the dial but I don't believe that's the case here. Any ideas would be greatly appreciated! Here's a link to the schematic...
http://www.freeinfosociety.com/electroni...hp?id=1804
I should also mention an alignment made no change....other than being able to move the one station that comes in strong...1470...back to about 1300.
First thing this symptom makes me think of is that your variable condenser plates may be shorting when you reach a certain point as they close, and maintain that short for the rest of the way closed. You may already have checked for that, but you didn't mention it.
Good thought...I did check for that. In fact, I even took a 1/4 wide piece of paper and tediously slid it between the fins with the tuning gang closed and was able to slide it through each side without problem. Usually when the plates are touching, you'll hear an audible click or pop when you tune through the dial and reach that point...this has no discernable leave off point...it's just the normal static. There are 5 different trimmers on the chassis itself, along with the 3 in each of the IF cans, so there are a lot of possible adjustments. The ones for the 540 end of the dial produce no change. I'd think it was a dirty tube socket, but if that was the case I don't think I'd receive any stations.
You might want to take a listen for your LO to hear if it is running below 1300kc. This will narrow thing down a bit.
Terry
The rotor could be going open on the tuning deck, make sure you are getting continuity between the terminal and the rotor plates.
Thanks Terry & John. Your help is much appreciated. I will look into those ideas when I head downstairs to the basement workshop in a bit. Will keep you posted.