^^^^ Surprise, surprise! That's how I do all mine! (even the "old" fm on the '42 model, works like a charm!!!). It sure would be swell to have all that fancy, schmancy equipment about and handy, but you have to do what you have to do! "Someday", perhaps, I'll have a scope or generator or both! So far, all of my units have been deemed "acceptable" to all that hear them. I can only imagine how well they would perform with a "real" alignment. So far, though, no complaints!
Electro, I'm happy for you but not certain how you know your "Old" FM is working properly as there really is nothing on that band. Tell us you did a full alignment on the modern FM frequency by ear and I will be really impressed. As for "fancy, schmancy" equipment, well, my signal generator was $25. My scope was free but not needed a lot. You must have better hearing than me, which everyone has. I suspect you could get even better response out of your radios with at least a signal generator. There is a difference between "acceptable" and great performance.
Regards, Jerry
A friend in need is a pest! Bill Slee ca 1970.
(This post was last modified: 09-12-2013, 11:01 PM by jerryhawthorne.)
Jerry, As Ron explained to me, I must be picking up 2nd or an odd 3rd harmonics or be close to the transmitters, or something. (Perhaps I did something when I rewired the radio with 20ga stranded, instead of 22ga solid????) As for it being "proper", it can't be, but I still pick up a minimum of 8 fm stations, (12 if I "tweak" the antenna) from about 88-101 mhz. (Yes, by ear) They sound quite good (but drift a little bit, sometimes, but seems dependent upon antenna positioning. A couple stations don't drift, nary 'tall! I think I should be able to lock it down with a modern antenna, maybe). Mine may not be "stellar performers", but they still kick proverbial a@@! I will be leaving this territory in the next couple of weeks, so my "radio days" will be drawing to a close, for now. (You may all jump for joy, and throw a big party!!! ) When I come back to it, you can bet your bottom dollar I'll have the equipment! May be awhile, though. Don't hold your breath!
Hey, no problem and glad it gets something. Just suggesting that a signal generator is a good and cheap investment. Sad to hear your leaving for a while but look forward to your return.
Jerry
The most likely circumstance is that you have high power stations in line of sight, and very closeby (3 to 4 miles, or closer). This allows the front end to overload, and creates a lot of intermodulation products. Combine that with a local oscillator that does not generate a perfect sine wave.
I don't know whether Philco uses low or high LO on their prewar FM sets, but especially if the LO is on the low side of the incoming frequency, say, 42 - 9 = 33 MHz. Tripling this (3rd harmonic is the strongest harmonic) gives you 99 MHz. 99 + 8(x3, remember you're tripling) = 123 MHz. So, you have a LO product of 99-123 MHz. Now subtract your 9 MHz IF from this, you get high side mixing product of 90 - 114 MHz. This does give you a possibility of receiving strong stations over most of the modern FM band, plus a bit of the aviation band.
Now, the math works out a bit different if they're using high side mixing to start with. 42 + 9 = 51. Double this gives you 102 MHz. This results in a LO range of 102 + 8(x2.. you're doubling here) = 118 so 102-118. Now, subtract your IF (102-9= 93) so your range then becomes 93 to 109 MHz. Still most of the band.
And all of this is possible because of high power stations and dirty local oscillators. At VHF frequencies, it takes a lot more effort to make a perfect sine wave.
YES! Math IS fun!!! Thank you very much for an overview of the in depth explanation, BAD!!! It is much appreciated! I suppose being in "the flatlands" of Texas helps matters out a tad, also, though I'm not exactly sure where the power station is around here, haven't really noticed.
I've just about got everything removed from the top of my chassis (except the adjustment coils in the square cans - so I'll have to come back and re-read this discussion on alignment later). I've got new caps (restuffed in the old cardboard tubes) and resistors and am just waiting for my wire to arrive and I'll redo the entire underside of the chassis.
In the mean time, I was pushing the tuning buttons on the chassis and this fell out of the mechanism somewhere. Any ideas what it is? Where it came from? Where I can find a new one? Do I only need one, or do I need several?
I managed to figure out the part from my last post, it looks like a rubber bumper for the buttons in the push button tuner. Does anyone know where to find replacements? I haven't found any online yet...
And on the topic of the push button tuner mechanism, what type of cleaner is best for cleaning the gunk out if the mechanism? Can I use some CRC cleaner and the Re-lube the mechanism with some WD-40? Or should I use something else?
I finally have some time this weekend and will begin replacing the caps, resistors, and rubber wire.
Eric, as for the bumpers, I have several fall out. Some were "alive" enough I could put them back in with some rubber cement. Some like yours were well, just totaled. I found the push buttons worked just fine without the missing ones. I don't know if anyone makes reproductions or not.
Jerry
Thanks for the tips, guys! Some CRC and WD-40 did a nice job on the tuning mechanism. All of the buttons are free now.
I used some naval jelly to remove a few spots of rust on the top of the chassis and have repainted the power transformer. A little metal polish and some steel wool has made a nice difference on the rest of the chassis.
I guess it's because it is my first time, but rewiring the chassis is taking a bit longer than I thought it would. I spent six hours today and have only gotten through the "easy" part of the chassis - the bottom side of the tubes on the left side of the chassis that are free and clear to work on. I'm becoming concerned about the density of wires on the right side of the chassis, under the tuning mechanism and coming out of those tower coils. I'm taking a number of pictures and trying to work carefully, so I don't mix things up.
So far, each of the caps is about 50% out of tolerance and each of the resistors still measure very close to spec. The wire, though, is a mess. Each rubber wire is just shredding as I touch it. So, I guess it is worth all of the trouble. I figure I still have another 6-10 hours of work to replace everything.
I can't wait to get it all back together and make it work...
I'm working on rewiring item #37 on the parts list, 2nd IF Transformer Assy. I've removed it from the chassis and pulled the core out. Surprise! There is a resistor inside that is not on the parts list. It measures 50k on my meter. Can someone please confirm the value of this resistor for me? It appears to have a gold (yellow), pink, and orange stripe on it.
If it's chocolate brown, I believe that's a purple stripe rather than pink, which would make... 47K ohm, yes? I don't have a chart in front of me and I'm a little rusty at decoding. And yes, I was quite surprised to find that resistor as well. (My secret weapon was several test leads in different colors... <<grabs yellow lead/gator>> "okay, I disconnected the yellow from *here*...")
Anyway, I've learned from the pros on here... "if it's a bugger to get to, replace it while you're already in that deep." Insert a timing belt joke here.
Thanks DeckApe! I've noticed that the color codes on the vintage resistors partially match new replacement resistors, but the new ones seem to have an extra color stripe in the code. On others, the colors are completely different, though they measure the same...
It's coming closer. Have one more IF assembly, a few wires, and a few resistors to replace then I can add all of the caps back. I'm getting anxious to fire it up and see what it sounds like!
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