05-13-2015, 09:32 PM
I just finished refurbishing (all new caps and all new resistors) my 39-30 last night. Thought I'd post a few findings here in case anyone else is looking for info on doing the same (and one question/issue I'm having). The radio was pretty much all stock electrically except for the first filter cap which had been removed and replaced under the chassis. The remaining two lytic cans were still connected, but leaked a white crumbly material out the top. I didn't power the radio (as I never do before a refurb), but the previous owner did and said it just "screeched". So I had no idea what to expect to find, or if it would work when I was done.
Like most 39 Philco radios, it was loaded with rubber wiring - half of which was crumbling. And only a matter of time before the other half started. That includes the PT, OT, and both IF cans. There were only like 4 cloth covered wires going to the tuning condenser and 2 grid caps. I replaced all of the rubber wire, even the stuff that still seemed pliable.
Someone had poured some kind of black tar/caulk material over the wires coming out of the PT. I had to cut that all away to take the shell apart. Once apart I had each wire marked and crumbled one, re sleeved it with the proper color heat shrink, and moved on to the next. Pretty much same thing for the OT, crumbled and re-sleeved the two wires 1 by 1.
I removed the preset buttons, coils, and trimmers completely to make it easier to work on the chassis. I had 2 push buttons that were sticky. Once it was out of the chassis, I laid it on some paper towel and shot some D5 into the 2 or 3 holes for each switch and worked them back and forth. I flipped the whole thing over and repeated the process. I replace all micas by default (personal choice - I only want to work on a chassis once and people have started seeing mica's failing more frequently in the past couple years and I lack the gear to test them) and from what i read these 370pF ceramic ones fail quite frequently anyway. I put a 360 and 10 in parallel to replace each one. I noticed the one attached to the coils was grounded to the bracket, while the one attached to the push button was grounded inconveniently to the radio chassis itself. To make it easier to reinstall (or remove again if I ever have to), I found a point to ground it to on the push button assembly that gets screwed to the chassis. Now removing the push button assembly would only require removing the black wire on top and the red wire on the bottom of the push buttons.
The bias resistor 45 (280 ohms) was a Micamold domino resistor. The package was bulged and looked heat distressed. Surprisingly it still measured correctly. I suspect it was either underrated to begin with, or just marginally rated at original line voltages and couldn't handle today's higher line voltages. I probably went a bit overboard here, I replaced it with a 100 and 180 ohm 5w 1% wirewound in series. That should more than cover any wattage/heat issues going forward. The 70 ohm was a regular carbon resistor in good condition, but read high (and I replace all resistors anyway - again I only want to work on a chassis once). So I replaced it with a 68 1w that was conveniently reading a little high at about 69.5.
The band selector was mounted in the most inconvenient way possible. And it had _a lot_ of rubber wires on it. I decided the easiest thing to do was to take it out. Before doing so I marked each wire with a letter or number sticker, and also place a matching sticker to where it terminated in the chassis. I then cut the wire as close as possible to the termination point in the chassis. I also took lots of pictures both before and after marking them and cutting them. Then I could work on the band switch mounted in a small portable vice on my work bench. I could cut new wires to pretty much exact lengths and even pre-bend them to match the path of the original, so when I put it back in they would be right where they needed to be. I replaced them one by one on the band switch along with the .05uf C3. I remounted the switch and reconnected all the new wires. I had removed the old wire stubs on the chassis ends except on the antenna coils. They are not mounted very securely and moved around too much when I tried to desolder and bend off the old leads. So I just added the new wires to the terminals with the old stubs still soldered on.
I came across what appear to be 3 deviations/run changes not documented in the info I got from Chuck. The documents noted two minor capacitor changes in run 1-1 (neither of the changes were present in this radio). The back was stamped "3-3", so maybe this was run 3-3?
The first was one of the tone caps (C39 .006uF) was .008uF. Probably not a huge difference. I recognized a similar circuit from my 38-10 (.008 and a .03 in series with the tone switch shunting the .008), so I kept it .008 since it came from the factory that way.
The second deviation was the fact they shielded the 37 tube. It has the trademark square base riveted to the socket. The drawing of the chassis in the service notes only show that around the 75, and Bob Andersen's chassis also lacked that base.
The third deviation caught me off guard at first. It's similar to what Bob noticed in his, but a different resistor value was used. In the schematic, the brown lead form the secondary of the primary IF goes to the AVC line with C3 to ground (assuming I'm understanding the circuit correctly). In the radio however, the brown lead is going to a 490k resistor and a .05uF cap. The other end of the cap goes to ground (this is not C3, that is buried under the band switch). The 490k then goes to the tap between the 280 and 70 ohm voltage divider off the CT of the transformer. Bob's was a similar change, except his had a 2M resistor instead of roughly .5M. When looking at other 39 chassis in my Riders scans, I happened to notice that this exact change is how they designed the 39-36. So for whatever reason, Philco must have been playing around with the 1st IF in this chassis and wound up mimicking what they did in the 39-36.
39-30 Schematic:
http://www.nostalgiaair.org/PagesByModel...013289.pdf
39-36 Schematic:
http://www.nostalgiaair.org/PagesByModel...013295.pdf
Other than that, no major surprises. A couple tubes tested weak, but I figured I'd fire up the radio first to see how it worked. Fired it up slowly on the variac watching the ammeter and B+ voltage, everything was fine. Radio came to life. Like Bob, I noticed that without a ground from the chassis to my house's electrical system the radio tended to pick up some extra noise. Not nearly as much as I heard in his YouTube video, but still noticeable. This radio over all seems to be more succeptable to noise than most of my others.
One of the weak tubes was the 6A8. With the weak one, I was seeing AVC voltages of -2 (no station) to about -6 (strong local). After I popped in the new one, I was seeing AVC all the way to -14vdc on a strong local, and about -10 on my SSTRAN. After replacing the 6A8 I did an alignment and was able to peak up the IF's quite a bit. Now the dial is tracking well, and the radio is working except for one small thing.
This radio has three tone settings. Basically the 1st setting is no bass (short out C26), 2nd is some bass (nothing shorted out), and 3rd is full bass (C39 shorted out). Any time on the setting is on 2 or 3, some distortion is introduced along with the bass. You don't hear it as much on talk radio. But on the music playing through my SSTRAN it's pretty apparent. The speaker cone is in good shape. There was just one little hole in the middle, but I patched it with a bit of fabric glue a couple days ago. I've checked the rest of the cone, everything else looks good. I would also assume if it were a cone issue, I would hear at least some distortion even on the no bass setting.
Any ideas on this issue? Everything else seems good on the radio.
Thanks!
-Nick
Like most 39 Philco radios, it was loaded with rubber wiring - half of which was crumbling. And only a matter of time before the other half started. That includes the PT, OT, and both IF cans. There were only like 4 cloth covered wires going to the tuning condenser and 2 grid caps. I replaced all of the rubber wire, even the stuff that still seemed pliable.
Someone had poured some kind of black tar/caulk material over the wires coming out of the PT. I had to cut that all away to take the shell apart. Once apart I had each wire marked and crumbled one, re sleeved it with the proper color heat shrink, and moved on to the next. Pretty much same thing for the OT, crumbled and re-sleeved the two wires 1 by 1.
I removed the preset buttons, coils, and trimmers completely to make it easier to work on the chassis. I had 2 push buttons that were sticky. Once it was out of the chassis, I laid it on some paper towel and shot some D5 into the 2 or 3 holes for each switch and worked them back and forth. I flipped the whole thing over and repeated the process. I replace all micas by default (personal choice - I only want to work on a chassis once and people have started seeing mica's failing more frequently in the past couple years and I lack the gear to test them) and from what i read these 370pF ceramic ones fail quite frequently anyway. I put a 360 and 10 in parallel to replace each one. I noticed the one attached to the coils was grounded to the bracket, while the one attached to the push button was grounded inconveniently to the radio chassis itself. To make it easier to reinstall (or remove again if I ever have to), I found a point to ground it to on the push button assembly that gets screwed to the chassis. Now removing the push button assembly would only require removing the black wire on top and the red wire on the bottom of the push buttons.
The bias resistor 45 (280 ohms) was a Micamold domino resistor. The package was bulged and looked heat distressed. Surprisingly it still measured correctly. I suspect it was either underrated to begin with, or just marginally rated at original line voltages and couldn't handle today's higher line voltages. I probably went a bit overboard here, I replaced it with a 100 and 180 ohm 5w 1% wirewound in series. That should more than cover any wattage/heat issues going forward. The 70 ohm was a regular carbon resistor in good condition, but read high (and I replace all resistors anyway - again I only want to work on a chassis once). So I replaced it with a 68 1w that was conveniently reading a little high at about 69.5.
The band selector was mounted in the most inconvenient way possible. And it had _a lot_ of rubber wires on it. I decided the easiest thing to do was to take it out. Before doing so I marked each wire with a letter or number sticker, and also place a matching sticker to where it terminated in the chassis. I then cut the wire as close as possible to the termination point in the chassis. I also took lots of pictures both before and after marking them and cutting them. Then I could work on the band switch mounted in a small portable vice on my work bench. I could cut new wires to pretty much exact lengths and even pre-bend them to match the path of the original, so when I put it back in they would be right where they needed to be. I replaced them one by one on the band switch along with the .05uf C3. I remounted the switch and reconnected all the new wires. I had removed the old wire stubs on the chassis ends except on the antenna coils. They are not mounted very securely and moved around too much when I tried to desolder and bend off the old leads. So I just added the new wires to the terminals with the old stubs still soldered on.
I came across what appear to be 3 deviations/run changes not documented in the info I got from Chuck. The documents noted two minor capacitor changes in run 1-1 (neither of the changes were present in this radio). The back was stamped "3-3", so maybe this was run 3-3?
The first was one of the tone caps (C39 .006uF) was .008uF. Probably not a huge difference. I recognized a similar circuit from my 38-10 (.008 and a .03 in series with the tone switch shunting the .008), so I kept it .008 since it came from the factory that way.
The second deviation was the fact they shielded the 37 tube. It has the trademark square base riveted to the socket. The drawing of the chassis in the service notes only show that around the 75, and Bob Andersen's chassis also lacked that base.
The third deviation caught me off guard at first. It's similar to what Bob noticed in his, but a different resistor value was used. In the schematic, the brown lead form the secondary of the primary IF goes to the AVC line with C3 to ground (assuming I'm understanding the circuit correctly). In the radio however, the brown lead is going to a 490k resistor and a .05uF cap. The other end of the cap goes to ground (this is not C3, that is buried under the band switch). The 490k then goes to the tap between the 280 and 70 ohm voltage divider off the CT of the transformer. Bob's was a similar change, except his had a 2M resistor instead of roughly .5M. When looking at other 39 chassis in my Riders scans, I happened to notice that this exact change is how they designed the 39-36. So for whatever reason, Philco must have been playing around with the 1st IF in this chassis and wound up mimicking what they did in the 39-36.
39-30 Schematic:
http://www.nostalgiaair.org/PagesByModel...013289.pdf
39-36 Schematic:
http://www.nostalgiaair.org/PagesByModel...013295.pdf
Other than that, no major surprises. A couple tubes tested weak, but I figured I'd fire up the radio first to see how it worked. Fired it up slowly on the variac watching the ammeter and B+ voltage, everything was fine. Radio came to life. Like Bob, I noticed that without a ground from the chassis to my house's electrical system the radio tended to pick up some extra noise. Not nearly as much as I heard in his YouTube video, but still noticeable. This radio over all seems to be more succeptable to noise than most of my others.
One of the weak tubes was the 6A8. With the weak one, I was seeing AVC voltages of -2 (no station) to about -6 (strong local). After I popped in the new one, I was seeing AVC all the way to -14vdc on a strong local, and about -10 on my SSTRAN. After replacing the 6A8 I did an alignment and was able to peak up the IF's quite a bit. Now the dial is tracking well, and the radio is working except for one small thing.
This radio has three tone settings. Basically the 1st setting is no bass (short out C26), 2nd is some bass (nothing shorted out), and 3rd is full bass (C39 shorted out). Any time on the setting is on 2 or 3, some distortion is introduced along with the bass. You don't hear it as much on talk radio. But on the music playing through my SSTRAN it's pretty apparent. The speaker cone is in good shape. There was just one little hole in the middle, but I patched it with a bit of fabric glue a couple days ago. I've checked the rest of the cone, everything else looks good. I would also assume if it were a cone issue, I would hear at least some distortion even on the no bass setting.
Any ideas on this issue? Everything else seems good on the radio.
Thanks!
-Nick
