Philco 90 Oscillator question
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Hi fellas - It's about 1 year since I electronically restored my Philco 90. Although it was working great for the most part, occasionally the channels would disappear for a minute or two only to return shortly afterwards. Since I had to rewind a broken coil originally I wondered if another had a bad connection so I removed the oscillator coil. The inner coil (34Guage) looked immaculate. The outside had some corrosion so I removed and rewound the same direction and number of turns with 34 Gauge. However, the wire looked thicker than gauge. I also found 1 resistor 50% over tolerance so I replaced and rechecked all resistors which weren't originally replaced (only 4). Afterwards, I turned it on expecting to give it a mild adjustment but it has a lot of static and the channels come and go. I'm assuming it's not oscillating. Any advice on the gauge and proper tuning would be greatly appreciated. Thanks-
Mark
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Hi Mark,
I think the general consensus is that original was 38g but I don't think that gauge is real important within reason. Direction is, wind it the wrong way around and it won't oscillate. Not enough turns will stop it from working, if you are close to the number of turns it may work but won't tune the whole range of frequencies. Will dropout at the low end of the band. Some will bake the coil at low temp to evaporate any moisture in the form. Water can drastically lower the Q of the coil (efficiency).
If you are sure you are winding in the proper direction then try adding a few more turns (like 3-4) and see if that snaps it back into operation. You can take a listen for it with another set tuned to the same frequency + the IF frequency.
GL
Terry
(This post was last modified: 03-08-2016, 06:35 AM by Radioroslyn.)
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Mark, have you cleaned the tube pins and sockets?
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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+1
Had a model 370 that would fade out and then start working properly. Turned out after some observation that the heater in the 27 (osc toob) was intermittent
My 76 has a dirty socket I think, one of the 45's filament dies out after a while. Audio level drops some and has a bit of distortion.
Terry
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Another thing to be aware of is that large wire wound resistor with the taps. I don't know if you replaced yours or not when you restored, but I had one on a model 70 that gave me fits. It would do about the same thing your 90 is doing. It was highly intermittent, and took me weeks to finally catch it in the act with test equipment in place. I replaced the bad section and it has been working. I need to replace the whole thing. It also feeds the screen grids on the 24 tubes (in a model 70). I don't know if it is the same on the 90 or not. A couple of notes: 1. The resistor looked kind of rough, like it has been rather warm at some time, instead of smooth and shiny. 2. I found the problem by measuring the cathode current of the 24a tubes and lots of patience.
If I could find the place called "Somewhere", I could find "Anything" 
Tim
Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44
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Thanks guys - after rewinding the coil and adding 2 turns per Terry's suggestion, my oscillator came to life again. Then I tuned the osc coil then I adjusted the set. It sounds consistent now but there is some static I can't work out. I can either remove all static but much lower signal strength or get a higher strength signal with static, about 1/4 turn backed off of the osc stop.
Also, when I restored it a year back I did clean the pins and tubes. Never did test the tubes though. I always swap bulbs to assess good from bad but probably not the best technique to use. All caps and resistors have now also been replaced.
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If you gnd the ant post does the static go away?? Maybe it's something local like a charger or an electrical device??
Terry
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hope you boys are doing well - so after rewinding the oscillator several times with (still) no apparent oscillation afterwards I noticed another issue that I thought was related. The volume would not adjust at all or when it did a crackling sound accompanied the radio. I them resorted to substituting all tubes and cleaning the prongs. Still same issue. today after troubleshooting again I happened to stick my finger into the IF adjustment screw and noticed that pressing in certain positions would completely eliminate the crackling and restore the volume control so apparently the calibrator screw is shorting out ...does anyone know if these can be restored or should I look for a replacement on eBay? I am so relieved that almost 1 year after my original posting I finally figured out what the H**l was going on... Thanks fellas
Mark
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Mark, is your 90 an early (PP-45 output) version or a mid (single 47 output) and which IF trimmer is it you are pushing on? Since it did not shock you, I'm guessing, it was one on the secondary side of one of the IF transformers (the ones on the primary side of the IF transformers have B+ on them.) If the trimmer is on the secondary side of the transformer and is grounded, the ground is provided by the mounting bolt. Make sure, the mount bolt is tight. I would use a clip lead from the chassis to the grounded side of the trimmer, to make sure. Sometimes these trimmers get corrosion between the hollow brass rivet and the back plate. This causes the ground to be intermittent.
Steve
M R Radios C M Tubes
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Hey Steve .. it is the trimmer on the first IF and if I touch the adjustment nut to ground directly I get full volume control back and no distortion. I took it off there's no corrosion at all beneath the nut. I re-assembled and you are correct that it is definitely a ground issue. I think the problem is within the trimmer itself though not the connection to the chassis is there a way to clean or restore it?
Mark
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The simple answer is to swing by and pickup this 70 parts chassis I've got.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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Sold!! Thanks Terry- I really appreciate it I'll give you a call this week sometime
Mark
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(02-18-2017, 06:00 PM)bdi1976 Wrote: Sold!! Thanks Terry- I really appreciate it I'll give you a call this week sometime
Mark
Hi Mark,
Did you give me a call in the last few days? I saw local # but I get a lot of spam calls. Am around pretty much all the time. Not much left on the chassis but does have the trimmers and you are more than welcome to grab it.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 02-18-2017, 06:50 PM by Radioroslyn.)
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Hey Terry I will actually be around your way today about 2 or 3:00 I'll give you a call when I'm in the area to see if you're around. I tried calling you a couple minutes ago give me a call if you need to thanks Mark
edit removed phone number please use pm for that sam
Posts: 82
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I replaced the wacky IF trimmer with an exact replacement from a 70 chassis which was also marked yellow but I have still have the exact problem... no volume control and lots of static unless I put my finger over the trimmer grounding it to the chassis with my hand which then brings it back sounding perfectly and restores volume control. Also any attempt to calibrate the oscillator or other trimmers just results in static and no improvement unless I make the adjustment while I'm grounding IF trimmer. one other thing to note my volume adjuster has a couple of dead spots in it where it binds so that needs to be replaced as well there's no chance that is related is there?
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