[andrekp]

BTW, my testing suggests that the local oscillator is faily close to being right on. Using a digital radio, the 42-324 tuned to just barely under 600, oscillates the digital at 1060, while the 42-321 tuned to about 1000, oscillates the digital at 1450. However, 1700 on the digital is oscillated by about 1210 on the 42-321 (which is obviously off by about 30-40kc)

So to me, this implies that my local oscillator is probably acting as it should - and is close to 455kc, but that for some reason the upper part of the band is off.

[exray]

My suspician is that this must be because the antenna tank trimmer needs tuning. I arrive at this conclusion through the idea that the oscillator should only adjust WHERE the stations are on the dial, but the antenna tank would control the spread of the band. I'm thinking that maybe the band pass of the antenna squeezes on the ends and it's currently adjusted so that it is above the middle so most of the dial is fine, but the top end is starting to get into the squeezed end.

The oscillator alone will determine the station locations on the dial. In a more sophisticated radio there would be two oscillator adjustments. A capacitor for the top end of the band and a coil or large padder capacitor for the bottom end. The combination of the two gives you the 'width' or spread. In this model you only have the top end adjustment. Thats not unusual and is generally effective enough.

Here's the alignment data in case you don't have it.
http://www.nostalgiaair.org/PagesByModel...013512.pdf
(skip that Part B about tightening the trimmers all the way down. You don't need to start from scratch on a working radio and that might cause you to get lost for sure!)

They have you aligning the dial pointer physically and setting the oscillator for correctness at 1600. Then they have you set the antenna trimmer while at 1500. You can do this with off air stations if you have something reasonably close. The antenna circuit trimmer will not affect the frequency.

Will your digital radio tune out of the BCB...up to 2055kc for example? If so you can use it just as you were describing and set the oscillator using that method if you don't have a local station handy.

Once it is set, and you've found a station to use to set the antenna trimmer, then go back and tweak the IF trimmers again. That's really all there is to it!

[andrekp]

Well, as I have it now, 610 is at about 620 on the scale, while 1530 is at about 1500 on the scale. That appears to be as close as I can get it to work. It still seems like the bandwidth is compressed a little bit (i.e. 610 needs to move down and 1530 needs to move up). (my digital is just another AM/FM radio, so it doesn't tune beyond about 1700AM)

However, while the oscillator trimmer has a profound and obvious effect, I can't hear anything going on when I adjust the antenna trimmer. If I tighten it all the way down, there is a very slight drop in volume, but once it's at all lose, it always sounds the same. I can unscrew it to the point where the screw is ready to fall out, but you can have a station tuned in and nothing at all changes when you turn the atenna trimmer.

I looked at it physically, but to be honest, I can see why it doesn't work - I just know the oscillator trimmer works, but the antenna trimmer doesn't. I took off the adjustment screw, and saw that it appears to be a simple cap with one metal plate connected to ground, a thin clear plastic sheet (presumably the mica dialectric) and another plate that it all screws down upon. Reads a small amount of ohms between the two plates (which is apparently the resistance through the coil which is in parallel) and this doesn't change when you screw it together (so the two plates aren't shorting). But it just really doesn't seem to DO anything when adjusted along its range. I even tried adding a small piece of paper along with the plastic, and it had no audible effect. Maybe the effect just is too small to be heard - I don't know.

It works well enough I guess right now, and maybe as good as it ever did, being so simple, so I guess I'll leave it as is for now unless anyone has further advice.

[exray]

On the antenna trimmer note that it is to be adjusted in the high end of the band. 1500 in this example. It won't have any noticeable effect in the low end.

Is the loop antenna in good shape? No shorted turns? And does the Antenna Transformer (#4) check out ok?

[andrekp]

Well the radio works beautifully - other than having a slightly squeezed bandwidth. There's no obvious problem with the internal loop, but then I'm not sure how I could ever test that other than visually, or winding a complete replacement.

I have been trying to adjust it at the top of the band. I am assuming the trannie is fine since a). the radio works well generally, and b). it reads about 3R5 across it, which happens to be exactly what's marked on the schematic. I'm more suspicious of that trimmer.

[Ron Ramirez]

Hi Andre

I just looked up your 42-321. Your set does not have a low frequency padder adjustment. This was included in better radios, including most older Philcos. Designed to be adjusted at the low end of the AM band, typically 600 kc, its purpose was to make the local oscillator track accurately with the set's IF (intermediate frequency).

Since the 42-321 does not have the low frequency padder, you are going to have to live with a set that is somewhat misaligned on the low end.

The bean counters, I am sure, deemed such an adjustment unnecessary on cheaper radios after a time. Hey, as long as it's close, who cares, right?

Finally, if you want the best alignment possible, you are going to have to invest in a signal generator and have some means of measuring the output, whether it be an output meter or oscilloscope. Then follow the factory alignment instructions to the letter. This is the only way you can accurately align your set.

The ear method is OK in a pinch, but is not the correct way to do things.

[andrekp]

Yeah, I've pretty much figured it's a close as it's ever going to get - which is actually fairly close at this point. Besides, it's just a radio on my own desk, not something I have to convince anyone else to live with.

I'm actually happy with where it's at, I just can't resist tweaking it further if possible.

That said, I did find it a little curious that the trimmer for the antenna tuning cap doesn't actually appear to have any effect at all - even given that whatever effect it's supposed to have is subtle. I suppose I could put a small value adjustable cap in its place and see if there's a difference. I could even disable the current trimmer and temporarily clip in a very small value cap just to see what change it makes. I feel it should at least SEEM to do SOMETHING!