[canerods]

Philco 41-240 (2 bands - broadcast and shortwave)
I've recapped this set and the Broadcast band sensitivity is exceptional - it's a very nice sounding radio. Unfortunately, the noise level on the SW band is very low and it hears virtually no signals. I've connected my ham antenna to the antenna terminal strip so you'd expect to hear at least something. I know from previous posts on the 41-250 that the three prong jack was for an auxiliary antenna. I'd guess the set would have been designed to use the cabinet loop antenna for shortwave in lieu of using the auxiliary antenna. BTW I have checked the antenna shortwave coil (7) and is not open. Does anyone have some tips on where to look next to improve the shortwave reception? :
Thanks, Joe

[Image: http://i181.photobucket.com/albums/x304/...loseup.jpg]

[exray]

If you are receiving NO signals other than maybe some spurs, etc, check to make sure the oscillator is working. You should be able to hear it in an adjacent radio tuned 455kc higher than the dial frequency. My 42-327 refused to work on SW and finally became wonky on BC as well and it turned out to be a bad mica cap in the osc circuit.

Even with the antenna connections incorrect you should hear *some* SW-BC around 6-7 Mc at night.

[Chuck Schwark]

Bandswitch contacts are notorious for intermittant contacts due to age/tarnishing. Clean all contacts and check for continuity.

Chuck

[canerods]

Thanks exray and Chuck...
I used detox on the band switch contacts and when a jiggle the knob the noise level comes up on SW, then drops back -- happens once in awhile, but not often -- it's very sporadic. I found this additional Riders schematic that clarifies the band switch/antenna connections for the 41-240. I confess, it's still greek to me. Looks like I got some work to do yet on this one.
Thanks,
Joe

[Image: http://i181.photobucket.com/albums/x304/...41-240.jpg]

[Chuck Schwark]

I hope you did not spray the contacts on the bandswitch, but used a Q-tip or small applicator to just the metal moving and stationary contacts.
"Flooding" the phenolic wafer structure can cause problems at high frequencies. The phenolic wafer sections will absorb and hold the contact cleaner. De-Ox-It leaves behind a lubricating compound and does not totally evaporate like other contact cleaners. This may cause stray capacitance between contacts on a wafer section and cause possible de-tuning and alignment problems.

[canerods]

Luckily, I used a small tube of the 100% solution to apply a drop to each individual contact. The continuity of the bandswitch checks OK. I never considered the problem of flooding the bandswitch with the de-ox-it...but I will save that useful tip for the future!!

[Chuck Schwark]

Then is sounds like poor tension in the contact leaves, since you say a slight wiggle of the swtich makes the SW background noise come and go.

[canerods]

Chuck:
Yes, it's in the bandswitch! If I switch it back n' forth many times... then all of sudden the SW band comes alive -- I even got WWV at 10 mhz with a short 18" wire connected to the antenna jack. When I switch it back to broadcast, I lose the SW again. I've checked all those contact leaves, they seem OK. I guess the good news is you helped me isolate the problem... many thanks!
Joe

[canerods]

Chuck... maybe it's NOT the bandswitch. The SW noise level is still intermittent. When I poke around the pins of the XXL rf tube, I hear static... then the SW band comes alive. The set plays normally for a time (15 minutes or so), then goes dead once more. When I poke the pins of tube again, I hear static -- see a tiny spark and the SW band comes alive again. I cleaned the tube pins and the socket -- to no avail. This never happens in the broadcast band... only on SW. Any ideas?
Happy New Year!
Joe

[Chuck Schwark]

Loktal tube pins and or loktal socket contacts need cleaning. Loktal sockets are notorious for this intermittancy.

[exray]

Thats also exactly the way my 42-327 did. I could pull the tube and stick it back in quickly and the shortwave would start. Couldn't duplicate the results from a cold start.

Loktal pins can be cantankerous and generally need cleaning with a fine abrasive (emery board, 400-600 sandpaper, etc). Regular electronics cleaner doesn't seem to do much good. The pins are some sort of aluminum alloy, iirc.

-Bill

[codefox1]

Ask your dentist or dental hygienist for an old scaler. This instrument is used to reach under the gumline to remove tartar, and they do get dull after a lot of use, but are plenty sharp for cleaning tube pins. Because it has a rounded blade, you can use it to scrape away some of the crud on tube pins. As others have stated, the loctal tubes do not respond well to normal solvents. I have opened boxes of NOS loctal tubes that were covered with a yellow powder on all the metal surfaces, and found I could scrub most of it off with ammonia and a toothbrush. With a little practice with the explorer, you can clean up the foulest tube in a few minutes. Of course the decals, and the tube designation itself may disappear from handling, and certainly with even a drop of ammonia. Personally, I like to get the grime and whatever else there is off my tube, but be warned. Write down the "name" of the tube you are working on lest you not know which one it is when it becomes clean.

Desperate measures to identify a tube include breathing on the top of the tube to reveal the faint etching of the number, and rubbing a little of your own skin oil, (nose or forehead is a source) where you think the number might be and looking obliquely under a strong light. More desperate measures include a magnifying glass, under 40 set of eyes, ohmmeter to locate filament pins, and finally seeing where the pins seem to connect to the superstructure (good luck on that one.) Of course, if you can identify all but one on the set you are working on, you're probably in good shape. Label it with a china marker which can always be wiped off, and proceed. I think most of us can distinguish between a rectifier, beam pentode, and if/rf amplifier tube, but a 6BA6 looks a lot like a 6BE6, and a 35L6 looks exactly like a 50L6, etc...

Loctal socket holes are a little too thin to use a pipe cleaner soaked in deoxit, which is my favorite for octal sockets. If you are really buddies with the dentist, you may be able to talk them out of an explorer. It's sharp point can help you force grunge out of loctal sockets as well as 7/9 pin miniature tubes. You can gently re-tension contacts with this tool, but don't use too much force, or you will either break the tool or collapse the contacts in the socket. It is also possible in some cases to take a socket female from a donor socket, or even one in the same set, i.e. one in the rectifier tube socket that is not used, and transplant it to a hopelessly fouled socket. If the socket shows evidence of arcing, or looks like a marshmallow that caught on fire at your last barbeque, replace it, for safety reasons. I have carefully cleaned and saved many spare sockets from junkers for a while, and if anyone needs one, please let me know. This is a hobby for me (at least until I get laid off,) and I would be glad to help out if I can.

[canerods]

I pulled all the loctal tubes and did a cleaning on all the tube pins. I scraped them with an exacto knife and emery board -- got them nice and shiny. I used a light coating of WD40 on them also. The intermittent problems are 99.9% solved. There's lot's of great info on this thread. Thanks everyone for sharing your experiences -- it's very valuable and much appreciated.
Joe