The PHILCO Phorum
Philco Model 81B - Printable Version

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RE: Philco Model 81B - Radioroslyn - 10-23-2022

>tried the sg at 460, radio about 550 but didn't get a tone

So did you try adjusting #20 and #11 to/till find the signal at 460KC? If not give that a try. Turn the signal output level up to high till you find the 460kc signal. Then go back and forth between the two trimmers IF for max signal with a low output setting on the generator. Then use #21 to set the level for max sensitivity by turning it inward till it starts to squeal. Then back it out a turn. You may find that when you adjust 20 & 11 the IF will start to oscillate. If so then back out 21 a little and continue to adjust 20 & 11. Conversely if the IF sensitivity is really poor screw in #21 a little after you find the 460kc signal. Then continue to adjust 20 &11.

I'm not sure if the 80 and the 81 use a fiber adjustment nut on the sensitivity control #21 like the later models do. The fiber nut are somewhat delicate and will crack and break when tighten. If it's tapered and looks like all of the other adjuster it's probably brass. If it's squared off on the end and has a screwdriver slot in it it's the fiber nut. Just be gentle when tightening. It doesn't have to be anywhere near tight when it's adjusted.

The voltages around the mixer look good but the cathode is a bit high. We can put a pin in it for now as it may have to do with the osc. It's low enough that it's drawing plate current. The detector voltages are kinda off but that could be because it not working and not near the point of oscillation. I'm assuming you've checked resistors #23 #25 #22. They are a common fault in the 80, 81, and 84's.

RE: Philco Model 81B - texan george - 10-25-2022

Sorry to take so long to get back. I finally got the 460 signal at close to 460. No signal after that. The sensitivity is the regular nut. I have gone thru this thing so many times looking for where the problem is but can't seem to find it. Pulled the osc coil and rewound it looking at the pictures I took prior, however I couldn't tell where it hooked up due to the wires being so corroded. I have the feedback coil on the same terminals as the cap/resistor items 5 and 10. Pulled the ant coil and baked it at 200 degrees for 30 min. It seems to check out ok. When I started, I changed all the resistors. Still no signal after the 460 tests. Here are the present voltages:
77 Osc- plate 252, screen 95, control 0, suppressor 76. cathode 76
77 Det- plate 60, screen 36.4, control .8, suppressor 0, cathode 0
42 - plate 234, screen 252, control -16, cathode 0.

It has to be something I just don't see.
George

RE: Philco Model 81B - texan george - 11-04-2022

Finally! after many hours on the phone with Terry troubleshooting this critter it works! Fixed some bad and incorrect wiring, rewound the ant. coil. I dont know how many times I rewound the osc coil, but it was a lot. Could not have done this without the help you can get off this phorum.
Thanks to Terry (Radioroslyn), his help and willingness to walk me through all the steps was amazing, and besides that we had some good talks and fun.
George

RE: Philco Model 81B - Radioroslyn - 11-04-2022

Aw shucks... it was nothin.

RE: Philco Model 81B - RodB - 11-05-2022

Kudos to Terry and way to hang in there George. Finding wiring errors long distance is one of the most difficult situations to do. Lots of mental concentration. It's a great feeling when it comes together.

RE: Philco Model 81B - radiorich - 11-05-2022

Hello George,
Wow that is great news and terry is really good at this he is the man !
I have been trying to help a friend the same way with his Sx-71 .

Sincerely Richard

RE: Philco Model 81B - texan george - 11-05-2022

Thanks for the reply's, Rod and Richard. It all goes to Terry, I was so close to packing it up and sending it to him, but my stubbornness and his help got it done. Once this front gets thru and the humidity drops, I will start on the cabinet. Not sure if it has the right dial, (p/n B-7989) it only goes to 150 without any marks above it for the police band. That is not a showstopper and the grill cloth I have won't be quite the right pattern but it's what I have left over. I will see how that looks as things go, can order new if needed.
George

RE: Philco Model 81B - texan george - 11-08-2022

Here it is, thanks to everyone especially Terry.
George

RE: Philco Model 81B - radiorich - 11-09-2022

Hello George,
Wow you have been putting a lot effort into this set as Terry said it sounds like the Power Transformer is shorted .

Sincerely Richard

RE: Philco Model 81B - texan george - 11-10-2022

Thanks Richard,
It took a while to get it done.
George