The PHILCO Phorum
Model 57 Doesn't Match Schematic - Printable Version

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Model 57 Doesn't Match Schematic - Pepperoni - 11-07-2012

http://www.nostalgiaair.org/PagesByModel/789/M0013789.pdf

When I disassembled this model 57 my 8ufd filter cap was connected to pin 4 of the 80 rectifier. Not the 4ufd. If the notes are correct the 8ufd terminal on the dual cap can is red and the 4ufd is green. Little hard to mix up.

My 4ufd was connected to a terminal strip where it met #11 (25K), #21 (1Meg) and some other components on the B+ line.

So obviously I'm a bit confused. I have another 57 coming over this morning that I can compare to but in the meantime, is there a mistake on the schematic or is the 4ufd handling the B+ line? And are the 4ufd & 8ufd + ends common to each other? Looks like they are through the speaker field.

Johnny

RE: Model 57 Doesn't Match Schematic - Chuck Schwark - 11-07-2012

That dual section electrolytic has the (-) sides common.
Also, I don't know if the common is also the can.

If it is, then there should be a cardboard sleeve on the lower end of the can insulating it from the chassis. You can see from the schematic that the (-) sides are NOT going to ground, but thru resistor 32.

Check the (-) lug/wire for continuity to the can to determine if someone left the sleeve off, which would cause no audio output tube grid bias, messing up audio.

http://philcoradio.com/tech/images/57.jpg
(Annotated schematic from Ron's site here.)

Chuck

RE: Model 57 Doesn't Match Schematic - Pepperoni - 11-07-2012

Chuck I got the other 57 in today and it's wired opposite of the one I have. The filter can is not grounded. The can has a black terminal on it that does go to B- and not chassis ground.

I think I'll put the one I have back together with the 8ufd going to B+ at the two resistors I mentioned earlier.

Thanks,
Johnny

RE: Model 57 Doesn't Match Schematic - Pepperoni - 11-10-2012

I have another dilemma that's driving me crazy. I have two model 57's. One I'm rebuilding and one that hasn't been touched. Both are identical in how things are installed and wired except the one that hasn't been touched yet has had new filter caps slaved in under the chassis.

Please look at the picture below and then compare that to the schematic. Nothing goes to pins 4 & 5 (which are jumpered together) of the 77 Det. Osc. except a red wire to the oscillator coil.

[Image: http://speakeasyradios.com/yahoo_site_admin/assets/images/Parts_001.314123414_std.jpg]

http://www.nostalgiaair.org/PagesByModel/789/M0013789.pdf

So why does the schematic show the #7 and #8 RC combo going to pins 4 & 5 of the Det. Osc.? Am I looking at things upside down or something?

And I'm not sure what the cap symbol labeled "A" is going to pin 4. It's not in the radio.

Johnny

Johnny

RE: Model 57 Doesn't Match Schematic - rghines1 - 11-10-2012

Pin 4 and 5 are suppressor grid and cathode respectively. It is common practice to tie these together.

Cap "A" may be what is called a gimmick capacitor. They are typically a pair of wires twisted together to form a few picofarads of capacitance. Not sure but could be used for neutralization. Some Zeniths used it such as the 8S154.

RE: Model 57 Doesn't Match Schematic - Pepperoni - 11-10-2012

Well that solves that mystery. There is a short wire that is on the oscillator that wraps around the wire coming from the volume control. Pins 4 & 5 on both 77's are jumpered together.

Any ideas on the big question? The RC circuit that doesn't connect to pin 5 of the Det. Osc. as shown on the schematic.

Johnny

RE: Model 57 Doesn't Match Schematic - rghines1 - 11-11-2012

Can you post a redrawn schematic?
Puzzled by your collage.

RE: Model 57 Doesn't Match Schematic - Ron Ramirez - 11-11-2012

Johnny

The 57 front end should be hooked up like this:

[Image: http://i326.photobucket.com/albums/k420/mrphilco/Phorum%20Stuff/57a.jpg]

Notice the 20K resistor (9) from the 77 screen grid (pin 3) to ground. Capacitor (7) and resistor ( 8 ) from the 77 cathode to the oscillator coil tickler winding; the other end of the tickler winding goes to ground.

But from your description, it sounds like things are hooked up as follows:

[Image: http://i326.photobucket.com/albums/k420/mrphilco/Phorum%20Stuff/57b.jpg]

See how cap (7) and resistor ( 8 ) are now on the other side of the tickler winding, with the top of the tickler going straight to the 77 cathode?

This is how the tickler and the cap-resistor network are wired up in Model 80. The radio will probably work either way, but I think I would follow the 57 schematic (first example above).

RE: Model 57 Doesn't Match Schematic - Pepperoni - 11-11-2012

Thanks Ron! That's exactly what the 57 schematic should look like seeing how it's wired exactly like the 80. (Your 2nd drawing). Both of my 57's are wired identically like your 80 drawing. My 57's aren't wired like the 57 schematic.

Rghines1, Ron has just supplied that redrawn schematic.

Johnny