No RF on 89 - Printable Version
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No RF on 89 - Patrick - 12-18-2020
This is probably something so simple that my mind can't conceive.
I recapped, re-resistored, re-wired, re-tubed, etc. re-wound the tickler coil. All other coils and xformers ohm out good. Voltages are all correct. Checked all wiring at least 3 times. None of the 3 sections of the variable are shorted.
IF aligns just fine, and I have an IF signal from the antenna (but it is weaker than farther down the line).
But I cannot get an RF signal out! Tried various frequencies, Nothing. I did notice that the wave band switch seems to make no audible change in the static (I do get static out of the speaker).
What am I missing?
Oh, as a side note, I used #34 wire on the tickler, but it ohmed out good.
[Image: https://i.imgur.com/GHZgg19.jpg]
RE: No RF on 89 - RodB - 12-18-2020
It looks like the oscillator isn't running. The tickler has to be connected in the cathode circuit so as to provide a positive feedback. If it's connected backwards, no oscillations. Also, be sure the oscillator cathode bypass cap you put in is OK and soldered well. Cold solder joints can shut down the oscillator. And the oscillator tube may not be able to do the job despite the tester results. Probably the most confounding problem especially in these earlier sets.
RE: No RF on 89 - Patrick - 12-18-2020
Well, you hit that on the head first try! Reversed the tickler coil, and now I have RF! It dropped out by itself after I adjusted it, but I think that's another unrelated problem that I'll look in to. Thanks!
RE: No RF on 89 - RodB - 12-18-2020
Excellent, onward to another task!
RE: No RF on 89 - Patrick - 12-18-2020
Let's go back to that one, first. Listening to a station around 1100khz. As soon as I try to tune to another frequency (higher), RF stops. I've got it to come back doing various things, such as injecting an IF signal and flipping the wave band switch. Once it came back by touching a probe to the antenna clip. Once by powering off and back on. Doesn't appear to be any loose connections or cold solder joints anywhere. But when it's working, all I have to do is carefully move the dial towards higher frequencies, and it shuts off. I disconnected the variable cap and slowly went through the intire range on all three, and never a short to ground. Perplexing.
It's like changing the capacitance by un-meshing the variable, shuts everything down.
RE: No RF on 89 - Patrick - 12-18-2020
O.K. I've figured out how to get the signal back. But the question is: what's happening?
Tune to a station anywhere below 1300 khz. As soon as I increase frequency past 1300, it shuts off. I turn the wave band switch to Police, and completely un-mesh the variable up to around 1550. Now I have static again. Return the dial to anywhere less than 1300 khz, and flip the wave band switch back to broadcast. Voila! Back in business. I followed this same procedure 5 times in a row, and it worked each time.
RE: No RF on 89 - Radioroslyn - 12-18-2020
Could be a couple of things:
It just doesn't like you. Heard you saying some bad words while you were working on it. No fix for this.
Dirty bandswitch
Lead placement. Leads around the osc coil may not play nice when too close or far from each other.
Faulty ground on rotor shaft on tuning capacitor. Or bad ground at chassis and tuning cap frame.
Check the wiring at the tuning cap that the connections are good and the wire is not failing.
Might try adding a turn or two to the feedback winding.
Weak mixer tube/dirty socket.
Happy Hunting & GL
RE: No RF on 89 - RodB - 12-18-2020
Patrick, I was just looking at the docs I downloaded from Nostalgia Air. The first page discusses possible solutions for your symptoms. One is to reduce the cathode resistor of the oscillator to 10K. Look at the other items to see if they have merit.
RE: No RF on 89 - Patrick - 12-18-2020
Just read that. Thanks. I'll go through the steps, and post what I find.
RE: No RF on 89 - Patrick - 12-20-2020
Just went through every step on the "Correcting Intermittant Operation" page, with the exception of #8, which is "Oscillator Coil Impregnation".
Could that be the culprit? EVERY time I increase the tuning cap (to 1200 Khz, exactly), it quits oscillating, and I follow the same procedure of switching wave band switch to police, tuning cap to max unmeshed (which brings back oscillations), tuning cap BELOW 1200 Khz, and wave band back to BC, and it works.
Rotor shaft on tuning cap grounded throughout entire movement, wave band switch good, etc. etc.
Bottom line: quits oscillating at 1200 Khz.
I even changed my shirt, and had a different breakfast. Didn't help.
RE: No RF on 89 - Patrick - 12-20-2020
Looking back, could rewinding the tickler coil be the problem? What does it do, anyway? Should I rewind it again, adding more turns? Since wiring it backwards stopped oscillations, is this where I should look?
RE: No RF on 89 - Patrick - 12-20-2020
Just read everything Ron wrote on this same problem. Going to rewind the tickler coil and bake it. I'll get back.
RE: No RF on 89 - Steve Davis - 12-20-2020
Patrick, the first thing to try is lowering the resistance of the cathode resistor. It will not hurt to go down to 7500 ohm. It could be the coil form has absorbed some moisture. Remove the coil from the radio and bake it @ 200 degrees fore about a half hour. Occasionally we come across a chassis that just will not respond to all the normal "tricks". In that case, Ron has worked out a fix that is guaranteed to take care of the problem. Take a look here Converting the Oscillator Circuit - Models 19, 71, 89, 91 (philcoradio.com) [url=https://philcoradio.com/phorum/showthread.php?tid=14919][/url]
Steve
RE: No RF on 89 - Patrick - 12-20-2020
Steve, I lowered the cathode resistor to no avail. I also rewound the ticker, also to no avail. Since I've got alot of time on my hands, I'm going to try Ron's conversion to a 6A7. Thanks for the post.
It'll be awhile to post my results, but I will do it.
Pat
RE: No RF on 89 - Patrick - 12-20-2020
Quick question: Mylar tape? No got. Where can I get? Can't seem to find it with usual sources.