Philco 89 oscillator issues - Printable Version
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Philco 89 oscillator issues - JohnSchw - 11-01-2020
I have been working on a Philco 89 and have issues with the oscillator (36 osc tube). I replaced the caps and out of spec resistors, and I had to rewind the osc and detector coils. The oscillator is running, but at a frequency of about 4.4 MHz, and does not change with adjusting the tuning cap. I would assume that if I had wound the coil backwards (it appears to be right) that it would not even oscillate? So far, I have not been able to find any wiring errors, so was wondering if anyone has ever had this problem? The radio did not have any tube shields so I had to improvise with what I had until I can locate the proper ones.
Doing a search, I ran across the thread by Ron Ramirez on converting the radio to use a 6A7 tube instead of the 36. After reading all the horror stories about the unstable oscillators in these sets, I have been considering trying it. What is the success rate among the ones who did this conversion?
In the meantime, I will continue to try to figure it out.
John
RE: Philco 89 oscillator issues - NostalgiaRadioTime - 11-01-2020
Have a read through this thread:
https://philcoradio.com/phorum/showthread.php?tid=8753
I seem to remember one of my coils was apparently wound backwards and flipping two wires corrected it.
Good luck!
RE: Philco 89 oscillator issues - JohnSchw - 11-02-2020
Greg;
If the coil was backwards, would it even oscillate? The frequency that ir is oscillating at (4.4 MHz) is way higher than it should be. The fact that the tuning capacitor does not change the frequency almost seem as if it is not connected. Without the tuning capacitor it could possibly oscillate that high? I disconnected the tuning cap and checked with ind. meter, and it does show change. Will have to recheck circuitry.
John
RE: Philco 89 oscillator issues - NostalgiaRadioTime - 11-02-2020
Not sure where I posted it (it's been 6 years since I worked on that radio which is now my profile pic on here)... I thought it may have been in that thread but I guess not. Thinking back, it probably wasn't the OSC coil that I had wound backwards. More likely it was the RF coil.
All three coils on mine were open and had to be rewound (OSC, ANT and RF). You probably read about baking the coils before you rewind them as they like to absorb moisture that can cause problems. And because there were SO many production changes made during it's long run, it's important to determine exactly which set you have so you're working off of the correct schematic. Lots of good information to scroll through here and schematic comparisons with all of the changes: https://philcoradio.com/library/index.php/shop-talk/model-notes/evolution-of-philco-model-89/
Not to discourage you but my model 89 was an especially stubborn beast and I vowed to run as far away from them as possible should I ever have the misfortune to encounter another!
I remember reading an article on them at the time and they were dubbed "the radio that refuses to be repaired"!
RE: Philco 89 oscillator issues - JohnSchw - 11-09-2020
GregV: Well, I finally got back to checking on this oscillator issue. I took your advice and reversed the winding---AND IT WORKS!!!
Thanks for the suggestion. Now to work on alignment and sensitivity issues.
Johnschw