[Lee Petrie]

Hi everybody , I'm new to your group !!
I've repaired radios for over 30 years and been lucky , none have stumped me so far , except this 48-1266 ! I feel it's the FM oscillator , the Philco service info. claims I should have -2 volts on pin 4 of the 7F8 , AM their is -2.2 volts / FM their is -.8 volts FOLLOWED ALL THEIR INSTRUCTIONS , -.8 volts and no FM stations !! Any ideas ???
Thanks : Lee Petrie Illinois

[Chuck Schwark]

I'll bet it's bad/dirty bandswitch contacts or conductive crud between contacts on the switch wafers decks maybe. Pin 4 of the 7F8 happens to pass thru two bandswitch contact sections when in the FM position, looking at the schematic. Could also be a bad/open/shorted FM osc coil on the same line there? If the FM osc is not running - no stations.

[Lee Petrie]

Thanks for your reply, Chuck / I feel I have hit those areas by checking continuity in the FM osil coil / rotory swt.s you talked about / I feel with some neg. voltage at pin #4 of the 7F8 tube [ -0.8 volts instead of -2 v ] ,it would mean something is tring to work !! COULD I HAVE A LAZY 7F8 TUBE in a marginal circuit "originally" ??? Does anybody have a "working" 48-1266 that receives FM !! I'VE TRIED 4 "NEW" 7F8's without success !!! Thanks, Lee Petrie

[49Stude63]

Well this is a strange but true story about a 7F8 tube on a 46-1209 and maybe this is just a fluke, I can only say what happened. On a 46-1209 that a friend of mine was restoring the 7F8 tube had 4 neatly cut tape squares on the rivet heads, since they were old one had fallen off when the chassis was being recapped. After everything was done the radio would not play, all sockets had been cleaned, tubes checked and a radio that played before service would not play after. So one last chance was to put the tape square back and the radio worked. So turn to another 46-1209, mine intermittent problem so I was talking to my friend and he told me the story of the little tape squares on the rivet heads, so what did I have to loose, I cut 4 nice little black tape squares, put them on each rivet head and no more intermittent problems. He said the squares on the other 1209 seemed to be factory original. I used the same tube, I had cleaned or re-inserted the tube many times and that did not make a difference until I put the squares on the rivet heads, after that it worked fine.

[Lee Petrie]

Hi , 49Stude63 I appreciate all and any suggestions , I've been fighting this radio for over a month !! Yes , mine too has the tape over the tops of the rivits on the 7F8 tube socket , again, one fell off while I was recaping , I figured they "did something" so I replaced it ! Did the 46-1209 have FM and did it work ??? Thanks for the input; Lee Petrie //// Did you ever get up to the Stude museum in South Bend ,In. ??[/b]

[49Stude63]

No the 1209 does not have FM on it only BC/SW but when I called my friend the one he found the squares on was the 47-1230 which is basically the same chassis but has one extra tube and FM on it. Both were related to the 7F8 and the tape squares. I never got to the Studebaker museum but I did go to a couple of the big swap meets they have in South Bend each year. When I lived in Michigan it was a fairly easy drive, being in Ga makes it a little tougher.

[Fred R]

Lee,

I have a 1266 here and I would have to agree with Chuck that bandswitches on these models especially when sitting unused for a while seem to give problems. Mine has the FM working but one of the IF transformers is causing crackling on AM and SW. My problem is probably due to either bad capacitors in the AM windings or silver migration on the mica. I haven't pulled them yet to check. I have a 48-485 I have used for 30 years and it developed a hum problem that would come and go. I bring this up because it uses the same type of locktal sockets as the 1266. It turned out to be loose rivets on the 7B6 audio tube. Philco returned the heater to ground through the gounding assembly with four ground lugs around the socket. The grid resistor is also grounded to this part. When the rivets made poor contact to the chassis, the hum was bad. Maybe this has something to do with those tape squares 49Stude63 was talking about on the 7F8.
Generally, I like the postwar FM Philcos as the engineering was unique, thought out well and not a copy of every other set on the market.
One thing with all 1940's FM sets I found is the local oscillators have a high output. Most radios, even other makes, will wipe out TV reception on non cable sets when tuning around. There really weren't many TV's to worry about interfering with then. With the 1948 Philco FM sets I have, they drift a little for about 10 minutes but become stable afterwards and perform quite well.

Fred R

[Poston Drake]

First of all, I am confused by this talk of voltage measured on Pin 4 of the 7F8 converter (Pin 4 is the cathode). I assume you are actually talking about voltage on Pin 1 (oscillator grid)? If so, the -2.2v you are measuring on AM is normal, and you would expect to see somewhat less on FM, the -0.8v would not be unreasonable and I suspect the FM oscillator is actually running OK.

I am inclined to think that Chuck may be right here, look for any interruption in the signal path, most likely in the bandswitch wafers.

Also check mica capacitor C418 (100 pF) for open and/or leakage. And check resistor R409 (should be 15K).

Also make sure pins of 7F8 are clean and that it is making good connection in the socket. This was a common problem with postwar Philcos in FM mode.

Also, if all else fails, go back and look closely at all areas of the 6AG5 RF amp stage.

Regarding the four pieces of black "friction tape" over the rivets on the 7F8 socket, these have been present on every postwar Loctal-tube Philco with FM which I have ever serviced. They need to stay in place.

Poston

[Lee Petrie]

Thanks to both of you, Fred R. and Poston Drake for you needed help! On your problem ,Fred , my crackling was caused by a leaking C302A cap. inside the IF can following the7R7 tube [27MMF] replaced it ,noise is gone ! Poston, your correct ,I'm measuring neg. voltage ,plus lead on pin #4 of the 7F8 and the Neg. on pin #1 W/a 100,000 ohm isolating resistor on the neg voltage ! I checked R409 tonight .it's ok , I'll check C418 later I"M NOT CUSTOM TO SEE MICA CAPACITORS GOING BAD !! The Philco service info claims -2v, you still feel -o.8v is close enough ??? What is the best way to CLEAN the waffer swt.'s and the locktal tube sockets , I've tried to clean them , you both may be correct and the problem could be their !! Thanks Lee Petrie