[BDM]

Ok, I aligned the IFs. All seemed to be working fine. I noticed occasionally there was a pop, and reception would drop, sometimes to nothing. Then it went out almost completely. This is only on the LW BCB and Police bands. Lower & upper SW bands are fine. If I touch the #77 1st detector grid cap, reception comes screaming back.
http://www.youtube.com/watch?v=IFSbfoqLw_M

Any ideas?

Brian

[Ron Ramirez]

Check B+ on the plate and screen grid of your RF tube, Type 78. Sounds to me as if it has stopped functioning? Maybe a dirty band switch? Worst case scenario...bad antenna coil.

[BDM]

I'll check that Ron. Wouldn't a bad antenna coil effect all bands?

[Ron Ramirez]

Maybe yes, maybe no. I'd have to study the schematic to be sure.

[BDM]

Thanks Ron. I'm at a loss right now. The band switch wafer looks good. The 110/pf cap has been replaced, not that would cause this. Without that coupling cap, it has nothing.

[BDM]

Ron, all tube voltages are within 5 - 10v on the plates, and within a few volts on the grids and such. All except the 1st audio #77 tube. Plate is at 116v and 36v on the SG. Not that I think that's the issue. But that sure can't be right

I can touch the wafer contacts opposite the grid point that starts at the wafer, and get the same results. So I know the contacts are working. Like I said, the lower & upper SW bands seem to function perfectly :

[exray]

Just to cover the base...reflow the solder on the grid cap of the 77, and on the clip as well - or even try a fresh 77 if you have one handy.

[mandh]

Sounds like a symptom similar to what I saw on my Model 60 when I first started working on it. No reception via the antenna terminal but received signals if I touched the mixer grid cap. Turned out to be an open winding in the antenna coil as Ron suggested. Make a resistance measurement of the antenna and RF amp plate coils to see if there is an open winding.

Harv, WA2AAE

[BDM]

Yes, I've actually used a jumper at the grid cap, and swapped out both the #77 & #78 tubes. I have a feeling it's the RF coil/coils. I'm going to check resistance. If it is, luckily I have a parts set.

[Texasrocker]

Ive also had a rash of antenna-coil probs recently! They were definately bad ( fully open)! However, sometimes we all forget checking the other things possibly causing some of the intermittent probs. I know I do!! Most of you techs here are "light yrs" ahead of me restoring these old Philco sets, period!! I have learned sometimes that going back over the tube-socket pin connects, tightening them carefully with needlenose pliers, running a tube socket cleaning brush thru them carefully, and adding abit of new-solder to the tubes pins-tips connections, and scraping tube pins clean with a exacto knife, can sometimes yield good results in ALL these old sets for ridding intermittent probs.Also, make sure there are no "cold" solder-joints on any of the IF trans connections! I just ran across this prob recently also on a Zenith. Go back over and add abit of new solder to insure good connections, and remember the tube-sockets pins connections can "never" be too-clean. Sometimes, our tube-checkers sockets are tighter than the chassis, but then again, tube checkers can Lie also! Even the Best ones!! The "best test" for any Tube is in the set it is designed for! Just tryin to help.

[BDM]

Ok, made progress finally. I got a chance to sit down with it this week. Ed(etech) helped out tremendously, so hats off to him. We found the primary of the Ant coil can was shorted, or something to that effect. I could tap on the can hard, and reception returned. I disassembled the can, and couldn't find a thing wrong with the primary winding But, the lugs underneath the trimmer can, were sticking out, and not bent down. I wonder if maybe they were shorting out to the side of the can?? Anyhow, I carefully inspected it, cleaned the trimmers, bent the lugs down. It's been playing for maybe 4 hours fine.........On I go.

Thanks for the assistance, and especially Ed

[BDM]

Odd, but in the Ant coil can had a slip of news paper which was acting like insulation. Now, I can read part of it. It has something to do with A Charles S. Starr, Henrietta E. Garrett, and $17.000.000.

Etech looked it up in Google, and look at what we found.
http://www.time.com/time/magazine/articl...-2,00.html

My best guess, given the time frame (1932 - 1937), and where this case took place. A Philco employee stuffed this paper into the can for some reason or another?

[etech]

I am really fascinated by that newspaper clipping. It was obviously put in that antenna coil can by an employee when the can was either manufactured or installed in that 116B. But why? Was it placed there as a joke or a 'note in the bottle' type of thing waiting to be discovered by future generations? Or was it to provide some insulation to prevent the lugs of the trimmer caps from shorting against the sides of the can? I guess we will probably never know.

Ed

[radiomikee]

I had one like this recently. Turned out, I had a broken wire hidden in the insulation to the plates of the RF Amp tube one stage earlier than the mixer tube. Tapping the radio, or changing bands sometimes got the wire ends touching, so it would play, but stop again quickly. After replacing that wire, perfection. I might try checking the pin voltages to the tubes ahead of the 77, and see if a wiggle here or there upsets things or corrects it. The point to point solid wire in these sets is pretty thin, and sometimes a little nick from the wire stripper creates a weak point where it later cracks.