[dconant]

Hello, Working on a Philco 89. I kept checking my work as I went along and all was well. I am now finished (so I thought) but have noticed I can not pickup anything below about 900 kc on the AM band. I think the oscillator stops running as I don't hear the squeal on another radio. Above that all is good. I thought I narrowed it down to the 36 tube being picky. I found one that worked through the whole range. Now that it is ready to go back in the cabinet I found I have lost reception below 850 kc. Any idea what might be causing this. I have another 89 and the 36 tubes I have all work in that one. 

Thank you,
Dan

[klondike98]

Here's a thread that Ron Ramirez did some years back with some insight into the troubles with the 89 oscillator:
https://philcoradio.com/phorum/showthrea...d=20#pid20

And another thread on 89 oscillators:
https://philcoradio.com/phorum/showthrea...#pid172164

[MrFixr55]

+1 on Bob's comments. Ron (God rest his soul) wrote extensively on the 89/19's "autodyne" converter. This info can be found in the library.

Check the tuning capacitor to make sure that the plates are clean and do not short. the aluminum in these caps sometimes corrodes and whisker-like strands of aluminum oxide can cause shorting. Use an automotive feeler gauge to clean. Some Philco Phriends have removed these caps, placed in a dishwasher or ultrasonic cleaner then baked dry, with very good results. There are big issues with the insulating materials of the tuning cap, trimmer and even possibly the tube socket absorbing moisture. Ron recommended baking the "oscillator" coil. Maybe try to put the whole chassis in the oven, but at a temp of no more than 150 deg F.

Good luck. Although Ron said that the 89 was repairable to a reliable state, IMHO (and not having the experience that many of the experts have), I think that the 89 came from the 7th ring of #&!! I repaired one for a friend, upgraded the 36 to a 77, rewound the coil several times, and finally got it working. This thing kicked my @$$, and it is coming back to me as soon as i fix the same guy's Model 20.

[dconant]

I have heard of the problems with the oscillator coil but not the other stuff mentioned on the phorum. I turned the radio on this morning and it is playing below 900kc. Strange. The radio has been in my basement for almost a year. I keep the basement dry at about 40%. I have not checked the 36 cathode resistor to see if that helps. Will do that today. I had done another 89 early last year and had no problems with it but not to say there are none because I don't play it much. The chassis on the problem radio is somewhat warped as in all 4 corners do not set on the bench. I checked the tuning cap thinking there were shorts but found none. I'll give the feeler gauge a go. May even try the baking the chassis at 150 a try. I have not rewound a coil yet but have a shadow meter waiting for me to do that. 

I have another 89 waiting for its turn. Get the good times roll.

[Radioroslyn]

Hi Don,

You can try lowering the value of #10 0r #20 But 1st I would pull the osc coil out and heat it up (heat gun) to melt to wax off of it. Inspect it for green dots of death. These are little dots of copper corrosion within the winding that are not quite all the way thru yet. If you see any green dots it's time to rewind. It's common on the cathode winding (feedback) to be intermittent of open. 40ga wire equals about 1 ohm per ft so 38ga is going to be a bit longer a 5 1/4'. This is a rough measurement

By baking the coil forms in the oven at low temperatures it releases the moisture from the form. The moisture lowers the efficiency of the coil (aka Q). This is a good thing.

https://philcoradio.com/library/download...%20146.pdf

GL w/y project! Back to 90 on the bench.

[dconant]

I'm about to remove the oscillator coil. I had already changed #10 to 6800. I didn't have a 7500. How low would I lower #20? It is currently the original 5000. Looks like might be a 1 watt but not sure as parts list does not specify. Can you confirm? My radio is code 123. Would oscillator cause lower frequency stations to fade in an out while higher frequencies don't?

Would it make sense to change the 36 tube to a 77? If so what would I need to do?

Thank you for the help.
Dan

[dconant]

The coil is out and it looks pretty good. Very little wax and just around small coil over larger one. No evidence of corrosion or ever having any.  Should I be inspecting the inner coil? If so is it going to be difficult to remove?

[dconant]

Coil has been baked and back in the radio now. No change. Still no reception below 900kc. Dead silence. Should I rewind the small coil that is on top of the bigger coil? If so what size wire do I use? I have seen anywhere from #38 to #42. I read somewhere that the schematic is wrong in stating the coil is 5.25 ohms. Mine is 5.2. The poster said it should read 1 ohm.

[dconant]

Sorry about all the messages I'm leaving. I'm just trying stuff and letting you know. I got my cheap scope out and put the probe on the stationary oscillator section of the tuning cap. I saw the frequency change from one end of the dial to the other. After removing the probe I find the radio plays from one end of the dial to the other. I don't get it. The scope is as basic as you can get so I have no idea what I was seeing. It just quit again. Put the probe back on and I see the waveform stops shortly before 1000kc but I pickup strong stations very weak until about 900kc. What I see on the scope between 900 and 1000 is the frequency does not change but after 900 the scope goes flat line. The probe is a low capacity probe scope on a Conar kit I built.

[Radioroslyn]

If that's the case then connect a small value cap from the test point to the chassis.

[dconant]

Hello, I would like to add some information on my problem since I have probably confused most of you and probably will continue although I hope not. I have done some considerable checking of my work and parts. I think I can safely say at this point I have found the problem. The tuning cap on this radio lays flat. By that I mean the stationary section is parallel to the chassis. On the front side of the chassis is where the trimmers are for antenna, RF and oscillator. There is a connection point under each of these trimmers (gangs) but nothing is connected there. This is the front side of the stationary fins. On the back side there is a connection point for each gang that have connections going under the chassis. I removed these wires and then did some continuity checks between the front and back. The antenna gang had about 340 ohms. The RF gang had .8 ohms. The oscillator gang had 45 ohms. I would have thought all of these would be close to 0 ohms. There are four screws for each gang two in the back and two in the front. I took the screws out one at a time and cleaned the threads best I could. I found some were not very tight but not too loose. After adjusting the screws by varying the tightness I was able to get the gangs around one ohm. I did not mess with the RF gang as it was under one ohm. After playing the radio multiple times and length I continue to have reception the full scale.

Anyone ever run into this? Is my problem solved or have I just disturbed the problem and will bite me later on? Can I run wires from the front to the back without causing a problem? I asked this as I'm afraid after multiple heat soaks the continuity problem will return.

[Radioroslyn]

So I have a question for you. I've been servicing a model 90 which one of it's failing's was the rf amp to mixer coil. Simple coil w/just two winding no taps. One side (pri) connects to the plate of the 24A rf amp and b+. The secondary connects to the grid of the 24A mixer tube. Primary is 92t 40ga wire and the secondary is 162 turns 32ga wire. The turn numbers are correct but the sizes are what I had on hand. Which one is going to have the higher resistance?

[RodB]

Hi Dan,

You have just described the reason, in just about every radio, there's at least one flat, braided wire, 1/4 to 1/3 Inch wide soldered between the stator and chassis. For oscillators and tuned rf circuits to run correctly there must be zero ohms at this point.

[dconant]

Terry I say the smaller the wire the more resistance.

Rob the Philco 89 does not have any braid connected to it. The stator has the connection to the coils and the rotor has the connection to ground. Maybe I have stator and rotor confused. How I remember which is which is stator is stationary and rotor rotates like in a motor. I think I will run wires from front to back of the stator connections.

I appreciate people following this thread. I will be investigating that coil for breaks at the connection points and checking stuff mentioned in the NA page. I think I have done a good job making sure the plates are not touching and have cleaned between the plates with pipe cleaners. There is no scratching when I turn the dial.

[RodB]

Yes Dan, you are correct. I often think backwards when discussing the stator. The rotor plates are connected to the frame by the spring leaves between each gang. Then the frame is grounded. The stationary plates are connected to their respective circuits. BTW be sure to swipe a small piece of solvent soaked printer paper between the leaf spring and the frame to remove contaminants. It clears up noise when tuning around the dial. But you said you don't have scratching when tuning. Maybe the 89 tuning cap wasn't advanced enough to have these refinements.

Terry, is that a rhetorical question? Doesn't the signal strength depend on the turns ratio (within limits of course)?