The PHILCO Phorum

Finally getting to this cathedral radio and as usual always instructive to go through and look at things closely to see where you are at. The listing did say it worked! Well, not brave enough to try it. So off looking underneath and testing resistance of all the metal stuff. Power transformer looks good, field coil looks good. E-caps have had some work in the past but still need to be changes. Checked the cadohm resistor from point to point and looked good. Decided for no real reason to test it from one end and just march down the line. When I got to the other end well, end to end measured shorted. Well that is weird, I said to my self. Who ever played with the caps in the past had really messed up. Cap 42 which should have the ground isolated and attached to the center tap was at ground! Looking closer, the little ground tab that should be in between the cardboard and the can was on the outside and grounded. It just added more capacitance to the input line and left the voltage divider for producing some negative voltages for the tubes without any filtering.
Might have worked, but I doubt well. On to working on the rest of the radio. Just fun to try to figure out what people did to the poor old radios.
Pictures as I work through the problems. With the e-caps done, might try to bring it up slowly. Just finished a new speaker to chassis wiring as it had 3 strips of zip cord. Looked ugly. Just having fun.

Jerry

http://www.nostalgiaair.org/PagesByModel...013205.pdf

With 42 grounded it will make the 6F6 run hot and distort the audio. Also kills the avc and bias on the 1st audio stage.
Terry

Good luck on your new adventure. It's always interesting to figure out someone elses "fix".

A little updated on the nice cathedral, the dang thing works really well. Getting LA last night. Problem is that after about 5 minutes of running from cold start, the volume drops substantially. All resistors (that I can find) have been checked and all caps have been changed out other that one that is really buried under the band switch. The only thing that may be suspect is the 6Q7 which one diode section that looks really bad on my tester. Will get another of those. Putting audio into the volume control, the level remains constant with no drop after warming up. Problem seems to be prior to that. Any one with ideas will be received with a warm welcome.

Jerry

Obviously the 6Q7 needs changing, but also you say you
checked resistors, but did you replace even the ones that
checked "good"? A resistor can drift off/up once current
is flowing thru it. I, as a general rule, do not trust older
resistors any farther than I can throw them. I would
replace them to eliminate one variable.

Also, check the 6Q7 socket pins and a possible "open"
intermittant coil in the last IF can. Tapping around
with a wooden pencil and tapping wiring in that last
IF and DET stages may help.

Typing out loud,

Chuck

Agree, easy and cheap enough to change all the small carbon resistors whilst changing the capacitors. Doing so eliminates points of failure now and for the forseeable future. I trust you have cleaned out the tube sockets and adjusted tension where needed as well.

Well, being somewhat lazy I thought I would first try Codefox's comment that of course I had cleaned all tube sockets. Duh, well I did now and so far it is running just fine for 60 minutes. Of course the garage is now colder than you know what. Waiting for another second detector from Gene, I guess just because one of the diode section is really weak. So far so good. Will post some pictures of the chassis and cabinet soon. Cabinet needs some serious GoJo and wax.
Thanks for all the ideas and thanks Codefox for reminding me of some the basics which I often forget. I guess it may act up again so I will try an extended few hour run in the morning.

Jerry

Aye. Resistance is futile.