|| PHILCO SERVICE HINTS & TIPS |
|PHILCO SERVICE HINTS & TIPS - NUMBER 42
Model 89 Oscillator Troubles or
"The Model 89 from Hell"
Excerpted from postings on The Philco Phorum, October, 2005
by Ron Ramirez
ANOTHER PHILCO 89 FROM HELL
It was inevitable. I'd read the horror stories about Philco 89 sets, but I had never experienced any of the difficulties...... Until now.
A complete chassis and cabinet restoration of a Philco 89L from 1933-34 was in order. The cabinet refinishing went well, and it was awaiting its finished chassis and final photo documentation.
The chassis was quite another matter. It's standard operating procedure for me to not only replace all of the paper and electrolytic caps and out-of-tolerance resistors, but also to go ahead and rewind the primaries of those pesky RF coils; since if they aren't bad already, they will be sooner rather than later.
Having done all that, I fired it up for the first time. Nothing. Found the primary of the 2nd I.F. was open, and replaced it with another unit.
Now the set would sometimes tune in stations, weakly; but more often than not, it would just squeal.
After spending most of the day tearing out what hair I have left, I suddenly found that sometimes, when I touched the antenna lead to the grid cap of the type 36 det-osc tube, the set would mysteriously come to life for a little while.
AHA!!! Having read about the trouble with the oscillator circuit in Philco 19 and 89 sets, I had already reduced the type 36 oscillator tube's cathode resistor from 15K to 10K per a Philco recommendation; but 10K wasn't enough.
What I ended up doing was trying different type 36 tubes until I found one that would work well in the circuit, and I also had to further reduce the type 36 tube's cathode resistor to 7,500 ohms. (That suggestion is made in Ghirardi's "Radio Troubleshooters Handbook.", p. 2-115)
That did the trick, and now the set comes right on and plays when turned on, without any "finagling." All it needs now is a volume control replacement, and it's good to go and ready to launch. WHEW!!!
The next night I was listening to the set to "cook" it. The 89 seemed to be doing OK - until I pulled the trigger on my soldering gun to do something else, at which point it quit working again!
To make a long story short, I robbed an oscillator coil from my "shelf queen" Model 32B (same basic circuitry, made to operate on 32 volts DC). Cooked it with a hair dryer, then rewound the open tickler winding. Installed it in the cantankerous 89 and...BINGO.
It came right to life, loud and clear. It passed my "stress test" of being picked up an inch or two from the bench and dropped repeatedly. I turned the soldering gun on and off; other things in the work room on and off; it kept on playing, rock solid.
I let it play the rest of that evening, and it didn't cut out anymore. THEN I declared victory.
Lesson learned: From now on, I plan to use heat to bake EVERY Model 89 oscillator coil I encounter. I am convinced that doing so will help avoid such problems in the future.
If you really get mad at your Model 89 or 19 receiver, you can convert the type 36 autodyne converter to a type 77 tube to make it more reliable and spare you the difficulty of sometimes having to select a type 36 tube that will work in the set. In fact, Philco made this change in 1935 during production of the Model 89, Code 123.
You will need to change the five-pin socket to a six-pin. And be sure you change the cathode capacitor from 700 pF to 1500 pF (.0015 uF). Use a cathode resistor of 8K ohms or even 7,500 ohms for most reliable performance. This part was 8K in the Model 89, Code 123.