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Philco Model 81B - Printable Version

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RE: Philco Model 81B - texan george - 10-03-2022

Thanks Terry,
Guess I will have to find a pt somewhere. Probably need to look in the library to see if any of the other 80 series radios have the same or similar pt.
again, I thank you for your help
George

RE: Philco Model 81B - radiorich - 10-03-2022

Hello George ,
Well I had a General Electric Console that also had bad power transformer .
Sounds like you are making some headway dealing with this set double check everything !

Sincerely Richard

RE: Philco Model 81B - texan george - 10-04-2022

Thanks Richard,
Going to do what I can to get this working.
George

RE: Philco Model 81B - MrFixr55 - 10-04-2022

Hi Texan George,

This radio uses 4 tubes, so there should be a lot of transformers from early 30s Philco 4 or 5 tube sets that will work on this Unit. This set uses 6V tubes and an 80 rectifier with its own 5V heater. I would think that the 80, 81, and 37-84 transformers should be electronically similar. even some of the 5 tube sets should work. If you found someone that got so )!$$ed off at their 89 from #&!! that they threw it against a wall, that transformer should work.

If you are trying a transformer from a non-Philco, The Donor set should:
-Be a 5 tube set (The 42 filament draws much more current than a 41, 6V, etc.
-Use an 80, 5Y3, 5Y4,5W4, etc. rectifier. Transformers from Philcos that used an 84 or similar rectifier
won't work unless you rewire the rectifier socket for an 84.
- Use an electromagnetic dynamic speaker. connected in the B+ circuit. The output from the Rectifier
secondary is higher, to account for the field coil.
- Be physically able to fit.

Good luck.

RE: Philco Model 81B - texan george - 10-05-2022

Thanks, MrFixr55
I should be able to find one that will work. As far as I know the model 80 has the same pt.

RE: Philco Model 81B - texan george - 10-21-2022

Installed a pt and cap block item 15 from a model 80. Only reception is one station on the low end with very low volume. Read all the post on Models 80,81, and 84 for similar
problems. One post on the 84 was about the cap placement in item 20 which would be item 24 on the 81. Checked and rechecked but they are in correctly. So now I am stuck,
where is the problem? One thing is that it was a mess when I got it, so the layout of components is not clear. Trying to go strictly by the schematic but I do get myself confused at times. Also tried to do an alignment but had no signal from sig gen at 1400kc. I did rewind the ocs coil earlier so maybe its not quite right.
Thanks,
George

RE: Philco Model 81B - radiorich - 10-21-2022

Hello George,
One thing I seen that helps is to use color highlight pens of diffrent colors and trace the wiring on the schematic !.
I will even use masking tape to make diffrent parts in the set .
Far as the coil that you repaired did you rewind new wire on the coil form and if so did you use the same gauge and lenght ?

Sincerely Richard

RE: Philco Model 81B - Radioroslyn - 10-21-2022

Set your generator for 460kc/400cy modulation. Apply this signal to the ant post and gnd the generator to the gnd post. Set the dial at 550kc or so. Turn the volume control up about 3/4 up. Turn up the generator's attenuator till you can hear it in the receiver. Adjust #11 and #20 for peak performance. Adjust #21 till the detector oscillates then back it out a 1/2 a turn. Repeak #11 and #20. This completes the IF alignment.

On these superhet regen sets the IF stage is where pretty much all of the receiver's gain is developed. Without it it's about the same as using a crystal set. The IF alignment is imperative to achieve good reception. If it's not working after the IF alignment it's time to check over the oscillator. Should be able to hear it's signal at 460kc above the dial reading.

Just got thru working on an 84.  https://philcoradio.com/gallery2/1937a/#Model_37-84B Mine has the older 6 pin tubes in the undocumented cabinet.

RE: Philco Model 81B - texan george - 10-22-2022

Richard, thanks for the reply, yes, I do use highlighters on the schematics that are blown up to 11X17. Rewound the coil on the coil itself.

Terry, 
Thanks for the info, I will do that later today (its 5:30 am, better wait until the wife gets up) I'll let you know how it goes.
George

RE: Philco Model 81B - texan george - 10-22-2022

Forgot to mention, nice looking radio, your 84

RE: Philco Model 81B - texan george - 10-22-2022

Terry,
Tried what you said and no good. I guess I will pull the osc coil out and rewind it again. There is something on the schematic I don't quite understand, it looks like a 3.9-ohm coil coming off of item 5 and 10 and going to gnd. On the schematic it is shown just below the osc coil. Is it a coil or a few turns of wire and where is it?
Thanks,
George

RE: Philco Model 81B - texan george - 10-22-2022

Got to thinking about my last post. Is that what is called the tickler? On my model 91 I believe it was on the bottom of the osc coil and had to be rewound. I dont see anything on the bottom of this osc coil, but there is something on the inner form that I can't tell where it hooks up.
George

RE: Philco Model 81B - Radioroslyn - 10-22-2022

>Tried what you said and no good.

Well we need to see what's up with that. It should work with or without the osc working. Try connecting the generator to the grid cap of the 77 mixer tube and not the ant post. Set the dial for 1700kc. Check voltages.

>a 3.9-ohm coil coming off of item 5 and 10 and going to gnd. On the schematic it is shown just below the osc coil. Is it a coil or a few turns of wire and where is it?

That is part of #12 the oscillator coil, the feedback winding.

RE: Philco Model 81B - Radioroslyn - 10-22-2022

>Is that what is called the tickler?

Tickler or feedback are the same. I don't have my 81 apart to look at the coil but I'm pretty sure it has the winding at the bottom on the outside.

RE: Philco Model 81B - texan george - 10-23-2022

Terry,
I set the sg for 1700kc and did not get a tone at the speaker, here are the voltages
77 det/osc plate 244, screen 63, control 4.5, cathode 21
77 2nd det plate 58, screen 56, control .6, cathode 0
42 output plate 226, screen 242, control 16, cathode 0. 

tried the sg at 460, radio about 550 but didn't get a tone, stated to get a tone with the sg at about 525. I did change the 4-meg resistor on the IF transformer to 2 meg as recommended earlier in the process. I also don't notice the osc on the 2nd radio test.
I guess I need to pull the osc and rewind it again. Wish I had a good guide for what post the feedback goes to, I stupidly didnt write it down when I redid it but maybe is just needs to go in the other direction.

Well that where things are as on now, what do you think?
Thanks for your help
George