04-28-2020, 08:57 PM
I was having trouble tracing wires because this set is so packed so I began clipping things out. The volume/on-off control did not operate properly so that came out first. It just would not clean out with contact cleaner (on-off was not working) so it had to come apart.
[Image: https://www.dropbox.com/s/nijf14ip2j2qmx....jpg?raw=1]
It just took a little direct cleaning of the contacts to get it working.
I then clipped out what I thought was Cap#25 (in post #11) and it turned out that it was actually a dual cap with the second positive lead hidden directly underneath. That mean that electrolytic is actually Caps # 23 & 24 in the schematic and are the "missing" filter caps.
That realization made me feel better about this set. So far I've found two modifications in addition to the removal of the speaker field coil (which is 53A on the schematic...tell me if I'm wrong...). The pins 3 & 4 (the two cathodes) of the 25Z5 rectifier have been connected together right on the socket. In addition the volume control pot has the wiper arm connected to trimmer #11 (which I don't think makes a big difference since the pot is a 3meg instead of the 500k called for in the schematic. I have read other restorations on this model that had a similar 3meg volume pot so it may have been a factory mod. You can see the physical connection in the photo above).
I've captured the changes in the following schematic where the green is the added connections and the red Xs are the cut out field coil:
[Image: https://www.dropbox.com/s/g434fq4ps8qq3j....jpg?raw=1]
The set has a filter choke that is separate from the field coil and it looks to me (at least so far) like the previous repair simply cut out the field coil when installing the PM speaker. Does that make any sense? Could that be why they tied the rectifier cathodes together? I have yet to find cap#25 but now suspect I won't find it since, if my thinking is correct, we now have a half wave rectifier instead of a full wave.
[Image: https://www.dropbox.com/s/nijf14ip2j2qmx....jpg?raw=1]
It just took a little direct cleaning of the contacts to get it working.
I then clipped out what I thought was Cap#25 (in post #11) and it turned out that it was actually a dual cap with the second positive lead hidden directly underneath. That mean that electrolytic is actually Caps # 23 & 24 in the schematic and are the "missing" filter caps.
That realization made me feel better about this set. So far I've found two modifications in addition to the removal of the speaker field coil (which is 53A on the schematic...tell me if I'm wrong...). The pins 3 & 4 (the two cathodes) of the 25Z5 rectifier have been connected together right on the socket. In addition the volume control pot has the wiper arm connected to trimmer #11 (which I don't think makes a big difference since the pot is a 3meg instead of the 500k called for in the schematic. I have read other restorations on this model that had a similar 3meg volume pot so it may have been a factory mod. You can see the physical connection in the photo above).
I've captured the changes in the following schematic where the green is the added connections and the red Xs are the cut out field coil:
[Image: https://www.dropbox.com/s/g434fq4ps8qq3j....jpg?raw=1]
The set has a filter choke that is separate from the field coil and it looks to me (at least so far) like the previous repair simply cut out the field coil when installing the PM speaker. Does that make any sense? Could that be why they tied the rectifier cathodes together? I have yet to find cap#25 but now suspect I won't find it since, if my thinking is correct, we now have a half wave rectifier instead of a full wave.
