New here, an 89B I'm repairing
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City: Macedonia, OH
Hi all, just joined. I've been restoring radios since high school, and I've got about 15 radios, ranging from a Westinghouse Aeriola Sr. to a 1953 Zenith. My favorite is my 1935 Silvertone 1845 console I bought from a used furniture store.
I've got an 89B that I'm working on, but it's being temperamental. Already replaced the line cord and electrolytics, and rewound the primary on one of the RF coils. This will definitely be a head scratcher. The front end is showing almost unity gain when feeding it a signal from my generator. It also doesn't appear that the 36 tube is oscillating, and I've got no signal at the IF amp grid. Clearly, I'll have to go checking more coils and making sure I don't have more open windings.
I found the right schematic for my set, but are there any voltage charts available? Might be helpful, since I found the open RF coil when the plate voltage on the RF amp was next to nothing.
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Welcome to the Phorum, Sparkydave. It sounds like you have a great project. When asking for help on a specific radio it is always helpful to post a schematic so the members here can help. If you are still looking for more info, I suggest you look over this site, especially the knowledge base. You'll be able to get a lot of info in your model as well as links to get you the needed info and parts.
Have fun!
Eric
Lake in the Hills, IL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
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City: Macedonia, OH
Thanks, Eric! It appears I have the code 123, run 3 chassis.
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Sparkydave, you might first check the feedback winding of the oscillator coil in series with the 36 tube cathode. This winding is notorious for opening up as it is wound on the outside of the main coil with a nitrocellulose insulating sleeve. The nitrocellulose decomposes over time, releasing nitric acid and corroding the copper wire. This is the usual cause of osc failure in the 89/19 moder radios.
Check the voltage on the cathode of the 36, If it is more than a few volts, them the winding is probably open. It is fairly easy to rewind this section of the coil to restore operation.
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Welcome sparkydave! I will bet the primary on the oscillator coil is open and there is some real good info on Ron's site that will help you with that model 89.
Gregb
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Sparky,
Welcome to the Phorum. Good luck with your 89B. I'm sure it will be a nice player when you get it working. I'm listening to my 19B as I write this and I absoltely love it.
I second the opinion that your problem is most likely the small coil attached to the cathode of the 36. On my '19, that coil was 27 turns.
Jon
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Dave, if you have to rewind your oscillator coil, remove the outer winding then, bake the form at 200 degrees for 30 minutes before rewinding. Also, replace the 15K cathode resistor with a 10K or maybe even a 7500 ohm.
Steve
M R Radios C M Tubes
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City: Macedonia, OH
Sorry for the delay, got sidetracked by a few things. Turns out that yes, the primary on the oscillator coil is open. Hoping for the same kind of success I had on the RF coil, but getting the coil out from the rest of the world is the tricky part. Thanks all!
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Finally got back to the 89B after a long hiatus, and I got both the oscillator and antenna coil primaries rewound successfully. I fired it up again, and success! I picked up some local stations quite well. However, it drops out tuning below 1100 KHz. It doesn't appear the tuner plates are touching. Would changing the 36 cathode resistor to 10K help the oscillator keep oscillating? It seems that it just stops oscillating below that point.
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How do you know it is not oscillating?
Did you try another radio tuned to the same frequency or else?
Ron as I remember had to go all the way down to 7,500 Ohm with that resistor.
I believe he also reccommends baking the coil.
(This post was last modified: 12-01-2014, 03:43 PM by morzh.)
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City: Morris Plains, NJ
By all means, upgrade the 36 tube to a 77 tube. It's pretty much the same circuit as the earlier version, the Model 19. The phenolic tube sockets are a source of nasty intermittents; if you can, replace those sockets; cleaning, pinching, and polishing them didn't do anything. .
With new sockets and the 77 upgrade, I've got a super radio that's a true "keeper"
Pete AI2V
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Hi and Welcome!
I would add a few more turns to the winding you fixed on the osc coil. Methinks you don't have enough positive regeneration (feedback) Jon's set the 19 uses a higher gain tube so it doesn't take as many turns. I'd try 4 more turns should do it. Two important notes: When you rewound it it MUST be wound in the in the same direction. If add the 4 turns and just improves the tuning but still won't the whole band add a few more turns.
GL
Terry
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City: Memphis, TN
Hey guys, repairing a Philco 89B run 123 with a 77 detector tube, found a broken and gree osc coil primary winding. How many turns do I need to put around it??? My wire is so corroded I cannot count turns or length.
Thanks much
Stan adams
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Looking at about 26 turns of 38G. You can use 34 or 36G if you don't have 38.
Terry
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