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Philco 89B won't oscillate! - Printable Version

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Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

I have  done a detailed Voltage check, along with a resistance check on my 89B. It WILL NOT oscillate! The O-coil isn't open but has evidently lost its Q. I also used a tracer/injector to inject signal into the top caps. Every one but the oscillator tube (36), I can hear my tone. But the 36 acts dead! Underneath, I can inject signal and get a tone on the coils, even on the block condensers that are in the signal chain.
So I am forced to pull the O-coil and cook the water molecules out. si-i-i-i-igh....well, there are only 5 wires attached to it.
If I have to, i'll install a 77 in place of the (*&(&%^$) 36. There's a how-to article on Chuck Schwark's Philco Repair Bench site for that job. I'll have to swap out even the tube socket! 36 is a 5-pin tube, 77 has 6 pins. And I will have to rewind the O-coil. That's a real job! Wish me luck! Icon_lol

RE: Philco 89B won't oscillate! - morzh - 04-13-2016

Don't de-solder the coil, bite it out as close to the pins as possible, then clean the lugs.
The wires should have a little slack to be able to solder them back when the coil is reinstalled.

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

You're right! It's ridiculous to try and save that 1/8" that was soldered. Sometimes I may have to solder a piece of wire in so as to reach. But the O-coil is hard enough to remove in the first place.

RE: Philco 89B won't oscillate! - Radioroslyn - 04-13-2016

So if you measure the resistance from pin 4 of the 36 tube to the pin on the osc coil that has the resistor (15K) and cap (700mmfd) connected to it what do you  get???

Terry

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

(04-13-2016, 06:31 PM)Radioroslyn Wrote:  So if you measure the resistance from pin 4 of the 36 tube to the pin on the osc coil that has the resistor (15K) and cap (700mmfd) connected to it what do you  get???

Terry

Terry, I don't see a resistor or capacitor going to the O-coil. But pin #4 of the 36 goes to pin 1 of the O-coil. From that point, I get nothing- open on the other 4 pins. . I get 8.5 Ohms from the top cap 36 to gnd. O-coil OPEN?

RE: Philco 89B won't oscillate! - Radioroslyn - 04-13-2016

http://www.philcoradio.com/tech/images/89v1.jpg      Parts #8 & 10
Well should be a cap and resistor connected to the osc coil. What is the resistance from chassis ground to pin 4 of the 36 tube

Terry

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

(04-13-2016, 07:34 PM)Radioroslyn Wrote:  http://www.philcoradio.com/tech/images/89v1.jpg      Parts #8 & 10
Well should be a cap and resistor connected to the osc coil. What is the resistance from chassis ground to pin 4 of the 36 tube

Terry

Infinity

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

Mine is code 123. That schem (as well as the one I have) is for code 121. I see the components you mean. Pin #4 36 goes directly to pin 1 of the O-coil on this one.

RE: Philco 89B won't oscillate! - Radioroslyn - 04-13-2016

You've got me a bit confused. The code 123 has a 77 mixer tube the 121 has a 36. If you have a 36 tube use pin 4 or if you have a 77 use pin5. http://www.nostalgiaair.org/pagesbymodel/877/M0013877.pdf

Ok now your are looking for #8 and9 (code 123)
The osc circuit is about the same just different tube.  If the connect your ohm meter to pin 5 you should be able to find a low resistance (like less than 10 ohms) connection on the osc coil that isn't directly connected to pin 5 if the coil is ok.

Terry

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

Mine is definitely code 123- With a 36 oscillator.

RE: Philco 89B won't oscillate! - Radioroslyn - 04-13-2016

Go with pin 4 and find #8 and 10.

Terry

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

Part 8 is a block condenser (8174-B) and the 15K resistor is across 2 pins of it. It has NO electrical connection to O-coil- although it DOES have connection with the interstage coil.

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

woops....Radioslyn gave up on me. Well I will look to see if there are running changes in the folder I got from our pal Chuck.  Wish he or Ron was here!
Edit: All kinds of changes in the coils! Ay ay ayyyyy Anyway pin 4 of 36 (cathode) goes to pin 1 counting clockwise from the bracket of the O-coil. from there to any other pin on O-coil is a reading called ol (nothing). Sounds like I will be pulling said coil. Yuck!

RE: Philco 89B won't oscillate! - Radioroslyn - 04-13-2016

No haven't given up yet. Was on another forum. Ok so if you look at the schematic find the cathode connection on the mixer tube. Follow it over and you will see that it goes over to a coil. That is the feedback winding of the osc coil. The other end of that winding goes to the 15K resistor and 700mmfd cap and then to the chassis. That winding is what is what we need to test the resistance of. There are two other winding on that same coil but those are usually ok. Also check the 15K resistor to see if it is open. Just for grins how much voltage do you have at the cathode of the mixer?? Should be pretty low like a few volts.

Terry

RE: Philco 89B won't oscillate! - Steve McDonald - 04-13-2016

That would be pin 4 of the 36-cathode. This goes directly to the oscillator coil, pin 1. this pin is not connected to the others. 15K resistor reads 12.8 K . One end of the resistor goes to pin 2 of the O-coil. The other end, to ground. And between pins 1 and 2, there is infinity.