Hello all, I am new to the forum. I am having fun with a model 60, have rebuilt all of the block caps, have added the wiring updates from the service bulletins, (all except the different compensators) and am having chirps and whistles on some of the AM stations and the SW band is very insensitive. (frequencies track properly on both dials, but I have to pump in huge amounts of RF to get a sound out of the SW band) I have cleaned and aligned it for the most part, and am looking for experienced owners who have been through this chassis and can help me with a few issues. What are the stage gains? Also, regarding the antenna transformer, does anyone know about the "extra" stage of the primary? (the one that reads .7ohms on the schematic) Someone before me had jumped one of the terminals to the chassis and it looks like it was this stage. Is this a tickler of some sort or a separate coil mounted on the bottom? What is it's value in mH? or is it a small part of the original coil? Any help would be appreciated. This unit is a challenge so far. I like to get them running as good as new or better, but don't know what to expect with this chassis. I know the old Police band is really the upper AM band and mine is not sensitive enough to pull in the upper AM stations (we have several here in Chicago) or even any static, but I can inject a very strong signal and can hear my tone. Thanks for the help in advance. Ron M.
OK, I found out about the antenna coil. I just took it out and checked it and there was a small primary that was damaged, so I rewound it and now the SW band works fine. My Am band still has some funky IF issues, as in when I tune to stations on the lower portion of the band, the audio is overpowered by whistles. Seems like they all track fine, and the higher on the band I go, they sound normal. I am using a signal tracer to hear them, though.
My real issue today is somehow, I have not been able to figure out why the audio signal is not appearing at the grid (or the plate) of the 75 tube. I've replaced the tube, caps, checked the resistors, and checked the volume control and still am working on getting sound out of the 2nd detector. I've injected a signal into my final amp (the 42 tube) and it works fine. ??? Help would be appreciated. Thanks. Ron.
Well, the audio problem was something incredibly stupid. After all of this time rechecking my recap job, wiring changes, etc. I decided to inject a signal into the grid of the 75 tube, and it worked fine, but not with the external grid wire attached. so, I removed the tube shield for the 10th time and examined the grid wire, and someone had passed it through the tube socket eyelet and it finally shorted out when I had put in the new 75 tube and slid the shield down for the 10th time!
Now, back to my squealing or heterodyning problem on the AM band. I checked again and I must have the newer IF can types as well as the proper compensating trimmers too, so I can now say that all of the newest mods are in place for this model. It is more sensitive for sure, but now I really do need help with finding the cause of my squealing only on certain stations, all of which are below 1000 KHZ on the AM band. Changing the length of the antenna affects this issue some, but does not correct it. I can adjust the antenna trimmer and it has a similar effect, of course. Any suggestions would be appreciated as now I can focus on this one remaining problem. I'm wondering if not using the wavetrap that Philco calls for is causing this issue? This is where I need someone with experience with this chassis to advise. Maybe someone can actually respond this time, I feel dumb talking to myself here!
Hi, Ron.
Everyone is probably away doing their Saturday evening things.
Quick question: Does your Type 78 IF amplifier tube have its tube shield in place?
Hi Ron,
Yes, my 78 shield is in place.
Hi, Was just wandering around the schematic trying to find a wavetrap. What component number did you omit?
Hi, I did not omit the part, I neglected to put one in as the service bulletins mentioned to do. It is shown on the "late model" schematic on Ron's site, but does not have any electrical values shown. It is Philco part number 38-6073. I have tried a few generic Miller wavetraps that cover the AM band, but since I'm not sure of what frequency they were trying to "trap" I didn't expect it to work. (It didn't) I'm starting to check the remaining coils and have the sinking feeling that I have to rewind the primary on the oscillator coil. The IF units look good and measure good, but there's no telling. Believe it or not, this radio was supposed to have been "gone through" already!
Thanks. Ron M.
Since you are receiving stations, I sort of doubt the oscillator coil is your problem, but if it is leaky (leakage between windings), all manner of weird things could occur.
If you should have to rewind the oscillator primary, please note it is wound counterclockwise. Most Philco coil primaries are wound clockwise. If you wind the primary of the Model 60 oscillator coil clockwise, it will perform poorly (if at all), will not cover the entire AM band, and SW performance will be very poor to nonexistent.
You mention the set was "supposed to have been 'gone through' already." Hey, maybe someone rewound the oscillator coil primary and wound it backwards? I've seen that occur before.
Ron,
I took out all of the coils and measured the resistance, and they all measure exactly to the ohm what they are supposed to. I checked with (2) meters. The only problem I showed was on the oscillator coil, which looks original, the primary tests at 11.5 ohms instead of 3.4 ohms. I pressed on the coil and it went down to 9 ohms and when I released, it went back up to 11.5. The wire used on this is very fine gauge, much smaller than the antenna primary or than the secondaries. Do you know what gauge to use? I show 18 or 19 windings, can you confirm this? I was thinking that this was not the culprit either, as the oscillator showed very stable all over both bands. I get intermittent gain increases when the unit is on for the first 20 minutes, then stabilizes. This happens with different 6A7 and 78 tubes too. If I use a 50 foot antenna, the problem is worse at the lower end of the AM dial than when I use a 10 foot antenna. The antenna trimmer seems to peak the 10 foot antenna better than the 50 foot. That is the state of affairs now, at least. Thanks for your help. Ron M.
All is well now. (Comparatively) I had not compared my radio to the "late" schematic very carefully and it already had the IF changes from one of the bulletins, but not the separate biasing of the 6A7 and 78. I had been mis-aligning the secondary IF secondary thinking it was the BC LF padder. I put the unit back together after removing the coils and testing continuity and I replaced the 110pf cap on the oscillator coil. I decided not to rewind the primary on the o-coil per Ron's suggestion and he was right, that was not my main issue. Now, the only problems remaining are an intermittent sensitivity issue while warming up. The unit "cuts in and out" but does not completely lose signal while warming up. I suspect that one of the IF coils is intermittent. Also the unit is not very selective but is sensitive. It sounds good and the AVC works fairly well. I cannot trace the issue to any component so any suggestions would be appreciated. At least I can use the unit now!
Ron M.
Ron,
Congrats! Other than your intermittent issue, it sounds like you have your 60 running about as well as it is going to. I have found that they are not exactly the best radios out there, but they were sold by the hundreds of thousands...