I believe this radio has a 1st IF issue, the primary is 66 ohms the schematic shows 34 ohms, the secondary is 71 ohms and the schematic shows 47 ohms. It looks different than the 2nd IF from below, I think the 1st IF was replaced with one of the wrong resistance. I sent 460 KHz tone from the tone generator, on the grid cap of the 6A7, it is very faint at the secondary of the 1st IF and strong into the primary.
The 2nd IF measures 36 ohms on the primary, schematic shows 34 ohms, the secondary reads 45 ohms the schematic shows 85 ohms which I hope is an error on the schematic, 85 ohms seems a bit high.
When the 460 tone is put on the secondary of the 1st IF, I can get the tone all the way to the output coil.
I hoping I can find the correct IF coils. I think the 2nd IF is probably okay and the original one.
On the 1st IF there is no short between the primary and the secondary. This radio has two compensators on the 2nd IF, I believe this is run #11 according to the Evolution of Philco Model 60 by Ron.
Thanks
Jim
Is it possible that the 1st IF currently installed is not designed for 460KHz? Is the existing 1st IF xformer trimmer tuned, slug tuned or neither? Maybe hook up the sig generator to the convertor tube and adjust the freq of the sig gen till you peak an output on the secondary of the 1st IF xformer. Maybe lead dress may be an issue. ensure thet the wire to the grid cap for the IF tube is not running too close to then IF can or tube shield (if used. )Also, how good is the IF tube. If the sig gen is not attenuated, you could be blasting through a bad tube. Also check the wiring and parts in the AVC circuit. an open may cause grid rectification and low gain.
Good luck
Thank you MrFixr55, will check this out.
Need some help on the wiring a trimmer #12 for 600kc. This is the lasted run #11 changed from trimmer #11 to trimmer #12. How is this trimmer for 600kc. to be wired. It looks like it is ground to pin #1 of osc. Will this work for trimming 600kc?
[
attachment=30005]
Yes, this will work the way the schematic shows. A variable cap connected in series with an oscillator coil is called a padder and is tuned at the low end of the specific band, in this case 600khz. Variable caps in parallel with an oscillator coil are trimmers and tune the upper end of the band.
I also found that the #12 padder has a wire that goes to the band switch, which when the switch is put in the SW band position the lead coming from the #12 padder mates with the 4100pf cap. which goes to ground. The band switch wire is connected to the same terminal as the lead that goes to the osc coil on the padder. The 4100pf cap was put in there to replace the trimmer #11.
Having trouble with tuning, getting only one station and weak. Recapped and new resistors. Can hear this station with signal tracer very well, radio weak.
Read some threads and things point to the osc coil. Here are my readings with all wiring removed.
These are the coils pin numbers
1 to top wire 4.2 ohms primary coil
1 to 4 2.3
1 to 5 3.8
4 to 5 3.8
2 to 3 3.8 secondary coil
The ohm readings are lower on the schematic. Do you think these are okay.
I believe the osc coil numbering is the same as the antenna coil, numbering clockwise from mount.
Align the IF @ 460kc by connecting a signal (460kc) to the grid cap of the 6A7. Does this improve the sensitivity?
Generally if you don't have any high resistances your good. If something was 100K then that would indicate a problem. Can you verify if the oscillator is running?
Yes I can hear one station weak with the radio but very strong with the signal tracer. I also used a test radio and could hear the whistle when oscillated. I believe the osc coil is okay, I took it out of the radio and it looks good as well. I can get the 460 signal thru the radio right up to the output coil/speaker. I can't send the 460 signal from the antenna clip thru the radio, but I can send 1400, 600 faintly? If you look at the schematic, on the antenna coil you will see a .7 ohm coil on the bottom, lug #4, I don't see that on this radio or measure it from #4. This could be the problem. Hopefully, tomorrow I will put the osc coil back in and remove the antenna coil and examine it. The antenna coil ohms out good.
Thanks for your reply
Oh, on the osc coil measurements I didn't subtract the resistance (ohms) of my meter leads. Better yet.
Ok. If you think the osc is working is it working properly The osc has to track the frequency on the dial or "in coming signal"+ 460kc. If you take a piece of hookup wire and wrap a couple of turns around the 6A7 tube. Take the other end and connect it to the ant post of a well calibrated sw receiver or freq counter. Osc frequency should always be 460kc high than the frequency the is on the dial. For instants if the dial read 100 (1000kc) osc got to be at 1460kc for IF stage to hear it. When you move the dial down to 60 (600kc) osc got to be at 1060kc.
Sets w/bad ant coils and good osc work ok but the sensitivity is awful. And can usually be tested by hooking the ant to grid cap of the mixer tube. When this is the case Set will track fine w/stations being where they are suppose to be on the dial.
Hello Jim,
It sounds like you are making some progress !
Terry great tip .
sincerely Richard
I thought I was doing ok. I have not removed the antenna coil, the coil ohms out great, but I do not see the coil which is rated at .7 ohms. on the schematic it is on the bottom on lug #4 of ant. coil. How important this is.
I was able to wrap a wire around the 6A7 then connected to my freq. counter and it worked ok, but not above lets say 1300 khz and above, if I touch the 6A7 cap or the #5 lug on ant. coil it will work ok. I used a transistor radio to test the osc as well worked ok.
Also I set the freq. generator to 460 khz and touched the grid cap of the #78 IF tube I get it loud thru the speaker, when I touch it to the 6A7, it is about 50% less. I do not get the 460 khz tone when connected to the antenna clip.
I can hear one station but very faint, it is at 1370 khz, on the dial as well. That station is the strongest where I live. If I turn the dial it will disappear. So the signal is right on. I do not get any hiss from the speaker either.
Is there a diagram for the band switch some where.
Thanks for helping me out this one is a bummer, just a year ago I restored a "60" went fine. I'm just not a good trouble shooter.
Seems to me the trouble is in the front end????
Here's how I see it. The ant coil is a red herring so far, I'm still back at the osc and 1st IF trans. Think of it like this. The 6A7 is pentagrid converter tube but inside it's a triode (osc bottom section) and pentode for the ant or rf section stacked on top of each other.
Pins 4,5, and 6 are all connected to the osc circuit. Pin 4 is the "output" of the osc in that it radiates throughout the tube. The grid cap (grid 4) has the signal from ant circuit. Inside the tube these two signal are being mixed together but there are three resulting signals at the mixer's output. If the set is tuned to 1000kc for instance you'll have a signal at 1000kc, 1460kc (in your case) and at 460kc. Philco I think is the only company that used 460kc IF's from late 1932 till '38. Then for a few yrs it was 470kc and finally 455kc in the beginning of the '40 season. By the late '30s 455kc was the standard but should always check the paper work to be sure.
So it's pretty important that IF stage is working properly to discriminate and pickup only the signal at 460kc . All of the trimmer for the adjustment of the IF should a pronounced peak. I like to feed the signal thru the grid of the mixer for the align of the IF rather than connecting it to the transformer. The generator tends to load the circuit which throws the alignment out a little.
If you have a spare 455kc IF input transformer I'd give that a try and see if it will tune up 5kc. Even one from an aa5.
The resistance measurements of coils don't really mean much, unless they are suppose to be a low resistance and read very high. Coils are all about inductance, Q, and resonance.