Working on the little AA5 AM / Shortwave Crosley model 56TXL I picked up last weekend and, after a complete recap, am encountering something odd. The set receives stations, but only for a second or two and they fade away. They're where they should be on the dial but as quickly as I find them they're gone. Even my overpowering sstran amt3000 disappears. I've swapped all the tubes with the exception of the mixer, 14Q7 which I don't have a spare. While I'm waiting for one to arrive, does anyone have any ideas on what could be causing this or have experienced it before? I still have a few resistors to check but this acts more like an OSC or ANT problem? It has the factory loop antenna attached to the back cover.
Here's the schematic:
http://www.nostalgiaair.org/pagesbymodel...003471.pdf
Oh no U again!!!!!!
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As normal I'm confused. When you tune in a station and it plays for several seconds does the set not recive any more? Set is dead?? If you tune it to another station does it just play for a few seconds too??
>> As normal I'm confused.
That makes two of us!
>>When you tune in a station and it plays for several seconds does the set not receive any more?
I can tune the dial slightly and the same station will come in again, for only a second or two.
>>Set is dead??
No, not dead just doesn't hold stations.
>>If you tune it to another station does it just play for a few seconds too??
Yes, then they fade away quickly too.
Ok have a look at the avc voltage. Connect the - voltmeter lead to the - side of one of the filter caps ( that's B-) and the + lead to the junction of #29 and 30. With a weak signal should see a small - voltage like .5-1v. With a strong signal could see -5 or 6v.
ps the set won't work as drawn in the schematic, plate of the 1st audio is grounded needs hv there. Dumb schematic!!!
Thanks, David!
Spent a while looking for the 47K resistor #30...then I realized it's in the IF can. I found the 3.3 meg #29 and it's attached directly to the volume control.
Doing your test, with no station I get -.6 VDC at that point.
When I get the strong local station to come in for a second or two, I get -1.8 VDC.
Am still wondering if, even though it tests OK, if that 14Q7 tube is causing this lack of station hold. I won't be able to verify that until I get the tube next week sometime.
Ok so w/a strong station does the avc voltage drop as if there's no station when it's misbehaving?
Yes as the station fades the voltage goes back to what it was with no station coming in.
Ok seems your issue in in the rf or if section. Try feeding a 455kc signal into the ant and hear if it misbehaves.
Seems to be a loctal tube socket problem. Pins are too loose in the 14B6 and 14A7 sockets. If I use my poker stick and hold tension on the socket against the pin it plays fine. But how do you tighten those little pin sockets around the tube pins?
Would it be possible to put a little solder inn the pin sockets to take up some of the space??? Yes I have been one with some Irish whiskey tonight.