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Ok. I have taken apart this radio and revisited the schematic many times over.
It tunes very well for the Osc and 1st Det., using the signal generator blasting out through the speaker - loud and clear. However, although at one time i had weak stations, I cannot do the next steps and tune the stations. i've looked at the coils and i cannot see a break in the wires. I've gone over and over the schematic and i can't find my error. I have to assume i am grounding it somewhere but having checked the capacitor blocks and resistors so much, I need to take a breather and see if you guys can point me in the correct direction. I don't know how i can put the signal generator on the antenna and hear it scream at 175Kh but not tune. I can hear peaks throughout the 600 - 1400 range but no stations. So signal comes out to the speaker but only a signal generated one. Does this point to a coil that i need to inspect more closely? Tnanks, Rich tuning is always my weak spot.
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Hi Rich,
A couple of things. Set your generator for 175kc connect output to the grid cap of the 24A mixer tube. Turn volume up and generator output so you can just here the signal. Adjust #15 and 17 for max tone heard from spkr. Now your IF is aligned.
Take a listen for the local oscillator. Set dial of 52 at 60 (600kc). Use another receiver to listen for the lo signal at 775. You can use a small transistor set near the 24Atube to listen with. The lo should produce a signal at 175kc above the dial setting. At 600kc on the dial lo is at 775kc with the dial set at 1000kc the lo is at 1175 you get the point.
It can be difficult to see a bad winding your better off using as ohm meter to do the looking for you. If the oscillator coil is open (common problem) you can measure the resistance from pin 4 of the 24A to the ungrounded side of #35 or 36. Should see a low resistance like 10 ohms or less. If not you'll need to rewind a small winding on the coil (it's easy)
http://philcoradio.com/tech/images/51.jpg
GL
Terry
(This post was last modified: 03-22-2016, 08:36 PM by
Radioroslyn.)
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(03-22-2016, 08:30 PM)Radioroslyn Wrote: Hi Rich,
A couple of things. Set your generator for 175kc connect output to the grid cap of the 24A mixer tube. Turn volume up and generator output so you can just here the signal. Adjust #15 and 17 for max tone heard from spkr. Now your IF is aligned.
Take a listen for the local oscillator. Set dial of 52 at 60 (600kc). Use another receiver to listen for the lo signal at 775. You can use a small transistor set near the 24Atube to listen with. The lo should produce a signal at 175kc above the dial setting. At 600kc on the dial lo is at 775kc with the dial set at 1000kc the lo is at 1175 you get the point.
It can be difficult to see a bad winding your better off using as ohm meter to do the looking for you. If the oscillator coil is open (common problem) you can measure the resistance from pin 4 of the 24A to the ungrounded side of #35 or 36. Should see a low resistance like 10 ohms or less. If not you'll need to rewind a small winding on the coil (it's easy)
http://philcoradio.com/tech/images/51.jpg
GL
Terry
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Terry, thank you so much.
I tried the lo but couldn't detect anything. However, i measured the ohms between #35 and pin 4 of 24A and i got a resistances of 18.24 M ohms (bouncing around) - that is far above 10 ohms so you put your finger on it. I kind of thought it had to be a coil but i didn't know how to tell. I measure 8.24 ohms on the heater pins. Now i know what the exact problem is - i just have to fix it. thank you again!
Rich
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Your welcome!
So the next step is to take some pic's of the coil while in the chassis to show the original wiring. Unsolder the connections and remove the coil. Near the bottom of the coil you'll see a small winding (about 20 turns or so). If you look closely you may see some green spots on that winding. That's where the copper wire has rotted. Count turns and rewind that part of the coil. It's rare for the other sections to be open. To rewind there is a couple of pointers. Direction is important! If you reverse the direction it will be out of phase with the other winding and will not oscillate. Use copper magnet wire, gauge isn't real critical. Original was 38g. You can use any thing from 32-38ga and it will work fine. Under that winding there is a strip of plastic, remove and disguard. I've used a strip of masking tape to replace it. Wind your winding over the tape. To get RR stamp of good house keeping bake the coil at low temp (150-175 deg) for 20min. You don't want roast it. The thought is that the Bakelite coil form holds moisture and that will lessen the Q (or efficiency) of the coil. I put a little candle wax over the new winding.
Put it back in the set and your good to go!! Easy!!
Check your PM box if you have questions.
GL
Terry
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Terry,
that's progress. Re-coiled because the the wire was broken. I measured resistance within each coil and they're reasonable - below 30k and much less in most instances. I followed the steps in the schematic and tuned the signal generator at 175 to the 24A mixer tuner - loud and clear. however, when i try and tune 175 with the signal generator at the antenna and the tuning capacitor at 1400 i get the signal generator but i cannot tune when both are at 600 plus there are no stations or hint of reception. my problem must be at the beginning now near the antenna and volume control. Thanks Rich
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If you are measuring anywhere near 30K across a coil then it is most likely open. You should be reading less than 100 ohms across any of the RF coils, and around 10 ohms across the oscillator coil.
It still seems your oscillator is not working. The 24A performs both the functions of the mixer and oscillator. It can still be passing the 175 kHz IF signal but not oscillating. If you can hear the 175 kHz IF freq at the 24A grid, then everything is good after the mixer, but you have no oscillator to mix the received signal with to produce the IF freq.
What you are probably hearing is the feedthrough of the 175 kHz IF freq into the mixer grid if you hear the same signal regardless of the position of the tuning dial.
(This post was last modified: 03-25-2016, 07:49 AM by
Mondial.)
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I re-did the oscillation coil and now get very low ohms across each. I checked the other 2 coils and found the same. I must be grounding the RF somehow. However, that doesn't make sense because i get such a loud 175kc when i connect the SG to the antenna. I can't get a signal beyond around 350kc - nothing above 600KC except when i clip on the SG and hear it regardless of the tuning capacitor. i think the RF coils are bypassed and i'm only getting the SG. Looking at that i don't know how that is happening.
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Ok time to push in the clutch pull the gear shift towards you and up (reverse gear). Lets go back a step or two. Now just because you have a low resistance across the winding you rewound doesn't necessarily mean the osc is working. To verify listen for it in another receiver as before mentioned. Also you can measure the voltage on the control grid of the mixer tube with a high resistance meter. Should read some negative voltage there. If positive the osc is not working.
Now if you like to fool around you can take your signal generator output and connect to the cathode of the mixer tube and use the generator for the local oscillator. Turn off the modulation when doing so. If you tune the generator 175 kc above the dial setting of the Philco and then tune both the radio and the generator together keeping the generator 175kc above the dial setting of the Philco you should be able to receive stations across the dial if the lo is the only issue.
Have fun
Terry
(This post was last modified: 03-26-2016, 06:04 AM by
Radioroslyn.)
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Well, i did play around with the SG as you stated and discovered a couple of things.
#1 the tube shield for the 3 tubes was wearing on the 24A oscillation wire bare going from the 24A cap to the hole connecting under the chassis. I kept losing signals and i never put 2 and 2 together - it ground out the IF signal. i will replace that wire after Easter.
But, now i can only tune to the upper level stations 1400 and above and even then only to one or so stations clearly. Anything below - nada. So i assume i didn't wind the OSC wire coil correctly. Was it not enough turns or something else? Your suggestions focused on the right things. Now that I'm close, i know this is not too far off. Thank you again!
PROGRESS!
Rich
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> Was it not enough turns or something else?
Mostly 2 things. If the turns are wound in the wrong direction or not enough turns will cause the osc to conk out as you go lower in frequency. So if you are pretty sure the direction is correct then I'd add 5 or so turns and see if that corrects the problem.
Terry
(This post was last modified: 03-26-2016, 05:24 PM by
Radioroslyn.)
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Ok, more wire didn't fix it. Still an oscillation problem.
So if two possibilities, then 1 is eliminated - i must have wired it in the wrong direction. Could be worse. Rich
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(03-26-2016, 10:59 PM)winston763 Wrote: Ok, more wire didn't fix it. Still an oscillation problem.
So if two possibilities, then 1 is eliminated - i must have wired it in the wrong direction. Could be worse. Rich
So that was worse.
Back to rewinding it my original way.
