[Phlogiston]

Well as I recall the mag tuning switch is 2 switches. Do they both work?

The AF tone is just something for you to hear. It is the modulation on an rf signal that you are injecting. Most people "tune" by listening to the volume of the tone, but NO tone is necessary you could use a volt meter.

This adjustment seems to be to center the magnetic tuning. The change in audio level is not great, nor is it very sharp. I recall hunting for it.

[BrendaAnnD]

Looking at your schematic, those tubes are a discriminator circuit, similar to those for FM reception, but these are used for your AFC (magnetic tuning) circuit. There will be no DC voltage on them at all, save for when the magnetic tuning is turned "on" and the radio is tuned off station.

[jerryhawthorne]

Thanks Phlog and to you Brenda. And yes, the discriminator circuit looks much like those of FM receivers. Pholg when you say that no tone is necessary, should I just turn it off on the sig gen tone? If so, if I have a VOM on the speaker, well, don't know what will come out but willing to try. Brenda, your a bright light here and appreciate your help and knowledge. I'm wallowing in a lack of knowledge on this circuit. I have not figured out where item 97 on the schematic is on the radio. Seems it may have a part to do with the mag tuning.
http://www.nostalgiaair.org/PagesByModel...013235.pdf

Jerry

Edit: Phlog as far as I can see the mag switch consists of a single switch (small rotary) combined to another switch on the back to change the "flood lights" on when the switch is turned to mag tuning. I replaced the switch as the old one had a broken up switch for the lights on the back of it. New switch seems to work well for both the rotary part and the lights.

[Phlogiston]

Yes, that is what I meant by 2 switches. One just runs the lights.

No, leave the modulation on. I was just saying that it is more of a matter of convenience riding on the RF signal which is what you are looking (listening) for. What I was responding to was when you said this:
"Not understanding how a signal (a tone AF) which I believe is going into that section is going to somehow alter the tuning of the radio"

If the circuit is working like an FM discriminator, deviation (modulation) would be required to see a voltage. So turn up the mod on your sig gen to 100% and hit it with a level high enough that no static or distortion is heard (like quieting the RX on an FM set). That AVC tube has a grunded plate. The dirrections state that you must be centered on freq for this step to work.

At this point I wonder how wide a signal your generator needs to output to see this, 5 kHz (?). Also, Check the instructions, but the IF bandwidth should be set to normal (narrow) while you make this adjustment.

My test for this function is just a bit backwards from the directions. I find a station, not strong or real weak, set the tuning with the "tone" IF narrow, mag tuning off. Then I tune off freq slightly till it is noticable. Then turn the mag tuning on and see if the station comes in better.

Did you check the 2 1M resistors on the grid, 56 and 59? And that 110mmf cap 57 on the 6J5 AVC?


How well did the radio respond on the tuning steps up to this point?

[jerryhawthorne]

Thanks for all the information, on to a little more testing. May have to wait until after the superbowl. Need to think a little more about the AVC as well if that is at all involved in setting of the mag tuning. Resistors test ok in the mag circuit.
Jerry

[jerryhawthorne]

Played with it a little today with monitoring the plate voltage of one of the 6J5 triodes in the output of the discriminator circuit and indeed, working the two tuning caps does change the plate voltage on the tube. It will go from 0 to about .3V DC and will peak. Not certain where I should be testing the "output" per the directions. Does the same with or without modulation. Much quieter without modulation. As I recall, hooking up to the speaker, don't see any change. Still confused as to how I should be troubleshooting this but then again, that's normal for me. Still not certain as well as to where to monitor the adjusting activity and with or without modulation. With modulation and monitoring the speaker output on my VOM I really see no change in the output while adjusting the padders.

Jerry

[jerryhawthorne]

Not understand the circuit and how to troubleshoot it, I have given up. Nothing I do seems to work for alignment as I understand it although that may be wrong. This dog will not hunt on the mag tuning. Not that it really affects the operation of the radio which is great. I would like it to work, but don't have the knowledge to figure this sucker out. So unless someone has some guidance, it has me beaten. Of course, Phlog could come out and visit.
Jerry

[Ron Ramirez]

All right, Jerry. You had stated that you had replaced the magnetic tuning off-on switch previously. Could it be wired incorrectly?

The way the switch should be wired is, when it is turned off the extra lights on the dial assembly are off - but the two wires going to the switch from the magnetic tuning circuit are shorted together by the switch, which disables the magnetic tuning circuit.

When the switch is on, the lamps come on but the short is removed from those two wires from the magnetic tuning assembly.

Using this info, study your schematic and I think you will see what I mean.

If you have the switch wired wrong, your lamps could be coming on with the switch in the on position but the two wires from the magnetic tuning circuit could be shorted, disabling the circuit.

Just a thought.

[jerryhawthorne]

Ron, thanks for jumping in. The mag tuning switch is fairly simple, turned clockwise (I believe) turns on the mag tuning and indeed turns on the lights (flood). That would not change the working of the on/off other than giving you a wrong light turn on for the flood if the four wires were wired wrong. One pair to one side with the 6V on that side and going also to the tuning light. Keeps that one on all the time. Moving the switch to the mag on position, ties two other wires to light the "flood lights". The other two wires going to the switch go to a small rotary switch that will take the two wires from going no where to grounding them. Even if reversed I don't see how that would make any differences. Yes that aspect of the switch works as indicated on the schematic.
As indicated earlier, following the alignment as I think I understand it, if measuring the output on the speaker with a VOM, I see no change in following the procedure for alignment. I can see a very small change on the plates of the the 6J5 output tubes from the circuit. They seem to do something but nothing on measuring a modulated signal to the speaker. I'm probably doing something wrong but trying to follow the directions.
A lot of help here for those of us electronically challenged.

Jerry

[Ron Ramirez]

You're close, but those two wires don't merely "go nowhere." They are actually very important. Perhaps you're not seeing the forest for the trees, or de trees for deForest, or whatever.

Okay. Pay close attention to the following.

38-116 Code 125 partial schematic.

[Image: http://i326.photobucket.com/albums/k420/...8f192d.jpg]

Pay extra close attention to part (96), the Magnetic Tuning off-on switch.

The 38-116 schematic, as well as this partial schematic, shows the Magnetic Tuning switch ON. Notice how the circuit is completed from the 6.3 volt source to the flood lamps? Notice also the other section of the switch is NOT connected between the parallel wires which go in one direction to the three capacitors of (65), resistors (64) and (88 ), and on to the discriminator circuit - and, in the other direction, to the magnetic tuning shorting switch (97) that is on the Automatic Tuning mechanism, and on to the 6N6G tube through resistors (28 ) and (29).

Now, look at this variation of a partial schematic, paying close attention to switch (96) again:

[Image: http://i326.photobucket.com/albums/k420/...250bf4.jpg]

This, which I just took the time to create in Paint Shop Pro, shows how switch (96) looks when it is turned off. See now how the 6.3 volt filament source is now disconnected from the flood lamps? Notice also the other section of switch (96) - it now shorts the two parallel wires. In this manner, when the Magnetic Tuning switch is off, the discriminator circuit is shorted out and Magnetic Tuning does not function.

If your switch is not connected as described, your radio's Magnetic Tuning circuit will never work right.

Please study these two partial schematics and get a handle of the circuitry before proceeding. Your radio will thank you.

[jerryhawthorne]

Thanks again Ron. I will check that switch. When I installed it, it had inadequate spacing as it tightened down on the chassis and wanted to short out the leads from the rotary. I will check that aspect again. Sorry I said the wires were going no where, bad choice of words. There were just single connections to each on the rotary switch. It seems item 97 could come into play as well. I have never identified where that switch is located! Will report back on the switch functioning correctly. Any idea where #97 is located?
Appreciate your help, know your busy.

Jerry

[jerryhawthorne]

More digging in and remeasuring the Mag switch and yes, it works nicely when monitoring it and takes each leg coming off of it and to ground when the switch is turned. Great! Problem is that when I measure between the two legs of the switch, they are always shorted together, regardless of the switch position on the front. Leads me to believe that that elusive and yet to be discovered switch labeled 97 on the schematic is not opening! I think! I may have to find that puppy but somewhat clueless as to where it might be. Perhaps on the back side of the tuning dial? But why? Disable the mag tuning somehow when using the "speed dial" feature. Still clueless in Sedona but trying. Am I safe to assume (scary) that switch needs to open for the mag tuning to work? PS: Ron, lovely job on the schematic, makes things much easier to review what is going on.

Jerry

[jerryhawthorne]

Still playing with it and I believe (often wrong) that the elusive switch mentioned above is the one behind the tuning dial with two wires going to it. Now, at what point in time should that switch open? It appears to be closed at all times. Regardless of position of the mag switch or speed dialing engaged. I would think that that switch should be open most of the time. Any inputs on the little devil? Wires on the switch don't look like an original solder job. Looks like someone has been back there in the past. Does not look like fun to get to.

Jerry

[Ron Ramirez]

Jerry, go to the following link:

http://philcoradio.com/phorum/showthread.php?tid=5938

Complete service instructions for the Philco Automatic Tuning mechanism. Study this and see if it helps.

I hesitated to post this, as I would prefer that Chuck get the business...every Service Bulletin that gets posted for free only serves to hurt his schematic copy service. So...my apologies to Chuck.

Yes, the switch - ( 8 ) in the Automatic Tuning Bulletin available in the link above, (97) in your schematic - should be open unless the lever is pushed in to change the radio to a different preset. When the lever is pushed in, the audio muting switch mutes the radio, and switch ( 8 ) - (97) on your schematic - shorts out the Automatic Tuning circuitry. And, yes, the two wires which attach from one side of the mechanism is for the Automatic Tuning shorting switch. The audio muting switch has but one wire connected to it, and I believe it attaches from the bottom of the mechanism.

[jerryhawthorne]

Thanks Ron, exactly the information I needed to understand the working and location. Nothing else to do but tear apart that mechanism again, except going deeper. I really needed to know when that switch should be open. Will report back with progress when I get up the courage. I did buy the schematic package from Chuck but it did not include the bulletin. Not surprising as it pertained to many different models. I am a Chuck supporter.
Jerry