The PHILCO Phorum

Evenin!

I seem to be having a little issue aligning the broadcast/police bands properly on this 41-315X. I can't get the entire band onto the scale. I can get it so I'm either missing 100 KHz in the upper portion of the band or the lower portion of the band on broadcast and about 700KHz on the Police Band. depending on which end I have it aligned to, it gradually goes further and further off the dial till I get to the opposite end of the broadcast band. I assume it's similar on the police band, but all I pick up there is Radio Havana it's off about 600 KHz.

when I'm doing the alignment I keep running out of adjustment (bottoming out) on 20 and 20a trimmers. I'm suspecting the osc transformer (32-2499). I've wondered about it since I first inspected it, it looks like it was messed with.








I replaced that Aerovox cap (not knowing for sure if it was mica or not) with a 2200 pf film cap. I have since replenished my mica caps and have a 2000 pf one, not sure if the values are far enough off to make a difference. but for now, the film cap remains.

The schematic conveniently leaves off the ohm measurements for the transformers. Was wondering if anyone knew what they possibly should be. I've looked at the schematic for the 41-316, it has values on it. seems very similar around that portion of the circuit. however, the nostalgia air schematic is missing the parts list, so unsure if the part numbers are the same or not.

Was wondering if anyone knew what the values ought to be, if using the 41-316 as a guide would be a good idea? does anyone have that parts list?

41-316 schematic Nostalgia Air

Thanks a Bunch!

Bret

Bret;

As a general rule when doing alignment of radios, adjust the inductor (if adjustable) for the low frequency end of the dial and adjust trimmer capacitors to get the top end of the dial, especially the oscillator circuit. Inductors in the RF amp circuit will peak the signal strength on the low frequency end of the dial and trimmers will peak the signal strength on the high end of the dial. If you hit a band that does not want to allow the trimmer capacitor to tune high enough it indicates that there is somehow too much capacitance for the circuit to tune that region. Some sets actually had instructions to the alignment requiring a technician to compress coil windings to peak the low frequency end of the dial and hand select fixed capacitors to allow trimmers to handle the high end of the dial. I notice there are two twisted wires on the bandswitch section to the left. This may be a gimmick capacitor or an inductance that was added to trim one band, although I can't tell which band would be affected.

Your 41-315X bandswitch and coil assembly looks similar to my 40-201, but has significant differences too. At least your set uses replacable mica capacitors in the front end. My 40-201 has some capacitors made with metal plates and mica sandwiched between them and a rivet holding them together! Those may be problematic if corrosion ever starts there. I wonder about the penetration of moisture. Of course trimmer capacitors always have that issue over time and you might want to examine them closely to see if there is corrosion of the metal surfaces that hold the mica in compression.

Joe

I would replace that 2200pF film cap with the correct value mica. That is a padding cap which sets the osc tuning range for the police band. Trimmer 20 is in series with this cap so it affects the broadcast band also.

The original mica was a tight tolerance cap (1 or 2%) and if it is off value it will affect the calibration especially at the low freq end of the dial. If you still have the original Aerovox cap you can reinstall it.

I have a feeling that there is nothing wrong with your osc coil and the real problem is the off value film replacement for the 2000pF mica.

Bret;

Mondial is right. That capacitor is in series with the rest of the caps and the coils in the circuit. As such, it will affect the tuning of the associated parts. Using film type capacitors in RF circuits is not a good idea as the internal parts are coiled up, thus creating an inductance, so you have not only changed the capacitance but the inductance as well. Use the 2000pFd silvered mica replacement and try aligning again. An alternative would be to use a NPO type 2000pFd disc ceramic capacitor. Disc ceramic capacitors and silvered mica capacitors have minimal inductance internally and that is just one reason why you see so many of them used in RF and IF circuits.

Good luck!

Joe

Thanks for the tips. I was wondering about the film cap.. I only did it because the schematic doesn't list it as mica. I came across a similar one of these in another set that turned out to be a film cap and the cause of a problem I had. Ever since then, I'm suspect of the larger mica looking caps that aren't listed specifically as mica on the parts list. I do still have the aerovox I could easily put it back or put it one of the new ones I got.

it was pretty maddening yesterday trying to get this to align. I'm just 140 KHz from my goal.. just an inch on the dial! Both adjustment screws are tightened completely and I just need another 1/2 turn, dangit.


Joe, I've hear about those coils. they had a nifty little tool for adjusting those too, didn't they? for those metal plate and mica caps. I have some of those in a box of philco parts I bought over the summer. was wondering what used those.

Bret;

The twisted wires I spotted are not a gimmick capacitor as I originally thought, they are a twisted pair of wires that form a transmission line between two RF coils/transformers. It helps keep the RF signals confined just to the area they are needed and also helps somewhat on rejection of outside noise and RF signals.

Joe

Are you sure? I traced it out, I thought it was #14 on the schematic which reads as a 1 mmf cond. I er... replaced it with a 1 pf mica capacitor....

broadcast band is still giving me grief.

replaced mica cap with the old one, tried again, same.. and a new one, same.

the 6.8K resistor was out of tolerance, so I figured while I was down there, I'd replace it. didn't make a difference either
time for bed!

Bret;

You may be right. Without spending considerable time looking at the under the chassis illustration and the switch wafer illustrations and seeing the actual chassis I cannot say for sure. The first schematic I looked at seemed to indicate it was a 10pFd cap, but the second one I looked at says 1pFd as you stated. C14 is not shown on the parts illustration page. It does say in the parts list that is made up of wires.

Joe

Hi,
I have two 41-295 chassis that I am still working on..one is for spare parts.
Neither have the twisted pair wires. I do not think they are C14 as many moons back I traced it down and believe I found the wire used for C14 but this was a long time back. My memory is not that great any longer. My gut feeling is this was some gimmick used for parasitic oscillation suppression on one of the bands??? Would have to trace it down and draw it up on the schematic to find out? John

Bret;

It is possible that the two twisted wires were a production run change. I was thinking that they used an approach similar to the 41-316 model where it shows two twisted wires in the RF section between two bandswitch wafers. It will probably take some detailed study. Perhaps someone has seen this before and can find a service bulletin or parts change notice on one of this family of receivers.

Joe

It would be interesting to know.

I'm still messing with the BC issue. I never pick up anything on any of my radios that high up in the bands everything seems to come in under 9 MHz and only after dark. then again, I'm inside a stucco building without an external antenna.

I do pick up my Signal Generator on the upper SW bands from across the room.

I do wish I could figure out what's wrong. I haven't done that many radios, but this isn't my first alignment, either.

You might try connecting a silver mica cap of about 100-220 pF or so across trimmer 20. This will decrease the tuning range of the BC oscillator and give a bit more adjustment.

Trimmer 20 is the padding cap for the BC band osc and should be adjusted at 580 kHz for proper tracking with the ant stage and accurate dial calibration at the low end of the dial.

Thanks Mondial! I'll give that a shot. I am almost there. just the trimmer bottoms out and my tone is @ 620.

I'm wondering if this was the issue it had when it was repaired last. there are an awful lot of those mica caps that were replaced around this area.

making progress.. it's still not tracking perfectly though. but it's mucho better.

I really appreciate the tips Mondial, Joe, John.

Shortwave comes in well, and the upper police band is on target.

I can't wait to get it against an outer wall near a window!