Hello All, I'm working on a 37-60 that was a rust bucket. It cleaned up really nice so I changed all caps and most of the resistors. Powered it up and got a local station right away which was surprising because I took this thing down to nothing to get all the rust out of it. Anyway I thought I'd give it an alignment since it was working. Did the IF part no problem, got peaks from all the trimmers. So I moved on to the SW part and seemed to go pretty good. When I got to Osc. and Ant. part of the Broadcast band the instructions said to turn receiver dial to 1600kc and signal generator to 800kc so it is using the second harmonic to adjust to 1600kc. When doing this I get no signal at 1600 on the receiver. Tuning thru the dial I get the signal at 1000kc. Then I noticed that the local station which is 970kc was coming in at 1170. So everything is off by 200kc. I tried adjusting the osc. trimmer to get to 800 but there is not enough adjustment. I run out after about 100kc of adjustment.
I may be wording this problem all wrong but if anyone has any suggestions I'd be grateful for any help.
Thanks
Dick
Oh - boy. Check for threads on Philco Coils, the failures and those that are detuned by moisture and age.
I would start by ignoring the direction and setting my signal generator to the receive freq and see what happens. After you figure it out, then, you can deal with images.
Russ
Thanks Russ I'll check out the detuning issue of Philco coils and hope mine aren't too bad.
Thanks for the quick response
Wouldn't fool with using the 2nd harmonic of anything these days your just asking for trouble. Try using a local station to set the bc osc. WMGW @1490kc is good for the high end. Tune the trimmer till the station is in the proper spot.
The easiest way is to use a counter and a loop around the mixer tube. This will give you a reading of the osc frequency as you set the trimmer. With a programmable one you can set it - out the IF offset set it read the direct frequency. When you do it this way there's no worry about images your looking as the osc and using math to know exactly where it needs to be.
Thanks Terry I can't get WMGW here in NE Ohio but I have a local station at 1360 that I listen to every day. As I was doing the alignment I thought the osc. screw on the trimmer turned awful easy. I didn't want to turn it too much so I kept trying other things like asking for advise. I decided to take the trimmer apart to sees what was going on with that screw and it was backed completely out on the back side. This trimmer has a screw with a flat head on the bottom and the other has the slot in the end of the same screw. Then the nut is the tensioner on the top side. So when ever I was turning that screw nothing was being adjusted on the bottom side, I THINK. So now I'm putting everything back together and we will try again.
Now when you say use a freq. counter and loop, what do you use for the loop? The input cable of the counter or a loop of wire attached to the counter. I have a Beckman Industrial counter but it is not programable. I used it to check my signal gen. when this radio kept being off by 200kc and the S.G. was within 5kc so not too bad.
Thanks Terry I knew you'd be chiming in some time cause all us wannabes need your knowledge and it is always forthcoming. That's why these forums are good fodder for our addiction!!
Dick
I never used the harmonics. Not sure why they do that. Zenith portables use that alot.
I use the required frequency straight out.
Dick
It's just a pickup loop (coil of wire) place around the mixer tube to sample the osc signal. If you subtract the IF frequency from the osc reading that will give you the receiver dial reading.
Maybe a little low grade loc-tite might stiffen the screws up a little or some non hardening gasket glue.
Mike
I think the reason for using harmonics was in the 30's generators were not all that accurate so by using a crystal osc and harmonic a more accurate adjustment could be made. Not sure why it would be done on the bc band but on the sw bands it makes good sense. THe 16B uses something like a 3.7mc xtal to adj all of the sw bands.
Thanks to Terry, Mike and Russ After removing the oscillator trimmer i found the screw had indeed backed its way almost all the way out and there was no pressure on the mica wafer. So I cleaned the mica while I was in there and reset the screw and started aligning again at the beginning. All went well this time and it's playing well out in the garage. Not so well in the house. Way too much RFI. Can't get rid of it. My bench presently is right next to my Geothermal heater and that thing puts out a lot of RFI. So I put in a bluetooth mod and right now it's playing off my phone " Stairway to Heaven ". I did have to swap out a 6A8 tube. The radio seemed to lose signal strength after about 30 min. of playing. So I tried a NOS 6A8 and 6K7 and it seems to keep the signal strength. Now to attempt to make the front of that cabinet look original with all the faux finish gone. Should be fun.
Thanks again
Dick