AM radio alignment question
This is my first radio project: Is a signal generator necessary to align an old AM radio, or can it be done wihtout one? If a signal generator is necessary and I don't want to spend a fortune on one, what should I look for in buying one? I have found several reasonably priced models on e-bay, but I am hesitant to bid until I get some advice from the pros (you all). Thanks,
It is necessary to align it properly, but if the set works you can optimize it without one. I don't own one myself.
A signal generator and a scope are particularly valuable for tracking signals through a non-functioning radio, and especially if your dial tracking is off that may be the only way to make it right.
It's not just a radio, it's history you can use!
Used signal generators are very inexpensive at antique radio swapmeets. Usually you can find a good one for $20 or even free.
Once you get a signal generator, make sure that it is well calibrated at the frequencies of interest (most notably 455 kHz). This can be done by listening for the harmonic at 910 on a well-calibrated (preferably digital, like a car radio) AM radio.
Using a signal generator makes alignment easier. You can often follow the exact alignment instructions from the manufacturer given in Rider.
Although it's handy to have, a signal generator is not absolutely necessary for alignment, especially for AM radios. With practice and a clear understanding of how all the tuned circuits in a radio interact, it's possible to align using over-the air signals.
We are fortunate to live in a time when some of the best test gear ever built is available for peanuts. Yes, you will need a signal generator. Do not waste your money (even if it's free) on junk like Eico, Heathkit, Paco or similar. These units are way off dial calibration, and put out very un-pure signals.They are also very poorly shielded. For $35 to $100 you should be able to land a General Radio 1001 or a HP-606 series. You will also want a frequency counter to monitor the output. Again, aim high. A GR-1192 can be had for $35. If you plan to continue with this hobby, you will be well rewarded for the money spent on these units.
I you don't have a digital radio or frequency meter to check your signal generator frequency you can use an "ordinary" radio. Tune in a station on the AM band and then feed some signal in from the generator (just clipping the output onto the aerial lead should do). Then set the generator to the same frequency as the station and adjust for a zero beat where it is the same as the station. Check the dial and either re-calibrate the generator or note the error. Do this for a number of stations, you can also beat the harmonics of the generator for lower frequencies e.g. 910 kHz second harmonic for 455kHz as already suggested. There probably won't be a station exactly on the frequency you want to use but you can find something close and use the error to offset the frequency you do want. For example, if you find the generator is reading 17 kHz high at 470 kHz (487) just set it 17 kHz high for 455 kHz (472) and it will be very close. The better generators such as the HP 606 mentioned have an inbuilt crystal oscillator and beat detector that's used to calibrate it, the 606 also has a vernier to move the dial reference to set it accurately but the method I suggested will do for a "cheap" generator.
Me too! Thats the very same gear that an awful lot of "radiotricians" used to repair an awful lot of radios in the 40's and 50's. If it was good enough for them to use everyday to make a living I figure it should be good enough for my limited hobby use. Just my 2 cents worth, your mileage may vary.
Check out this thread, which goes over some of the points you were wondering about:
And also this one, which gets a little more technical:
Both of them have a lot of interesting thoughts on alignment by John Grady (jgrady).
I have a signal generator, but honestly if the radio plays, I usually start out by using the method described by tubbytwo in the first thread above. (I do make a careful note of where the various trimmer screws were positioned, so I can always go back to square one. At least in my experience, the IF cans have needed virtually no adjustment after a recap -- maybe I've just been lucky.
I have a Precision E-200C signal generator that I picked up on eBay for less than $20, and it arrived calibrated absolutely perfectly and doesn't drift at all. I have a signal counter, but it's actually much easier to check the output of the generator by zero-beating it against my Timex digital clock radio. Of course, this wouldn't work very well for very high frequencies, but it's great for IF frequencies.
I wouldn't try to align a 4-band shortwave radio without a signal generator, but you can do pretty well without one on an AA5 as long as someone didn't "tighten down those loose screws" on the IF cans.
Before I got my E-200-C I got by with either peaking on a known station that was close to my alignment freq and/or using a cheapy heathkit test oscillator that only had the common alignment freqs on presets. Most if the common AA5s that I did only needed a slight adjustment after recapping (within 1/2 turn) in order to get good sound and dial tracking.
It's true that these consumer grade generators work OK if calibrated etc, but I think the point Chuck was making is that for a few bucks more you can get a much higher quality piece of gear today. If you have a small collection of AA5's it isn't worth the added expense, but a fleet of 12 tube consoles or a few boatanchors will justify the difference in cost. Imagine being at a flea market and standing beside two radios, a Hallicrafters S-38 and a Hammarlund SP-600, there's only $20.00 difference in price, same condition, which would you buy?? I'd go for the SP-600. (assuming the S-38 isn't grossly overpriced) As someone who has used all grades of gear, I can certainly appreciate a HP over an Eico. Just my $.02 Ross
One unit that many seem to ignore is the RCA WR50-c. This is a solid state unit, but it has crystal controlled 455 Khz and 10.7 Mhz settings to accurately align AM and FM if's. There are the usual VFO settings and you can also plug another crystal into the front panel if you need some other frequency produced very accurately.
It is very compact as well. I think I paid 12 or 13 dollars for mine on Ebay. I also have an Eico 324 and a Heathkit unit ( can't think of the model # at the moment), but I use the RCA most of the time.
The results of an allignment job depend on 1)How well the "restoration" work has been done. Were all the "usual suspect" parts like caps/tubes etc done correctly. or are we just "fixing it up", and replacing a tube or a cap to get it playing to some degree?
2) The quality of the test gear used.
3) the skill and knowledge of the person behind the allignment tool.
Each of these factors will limit the results. One who chooses to use low end test gear does so at their own peril. One of the biggest limitations of cheapo test gear is that they do not use regulated supplies. This applies to such as Eico, Heathkit, Paco, precision, Philco etc etc. None of this stuff is "lab grade". A VTVM from any of the above makers will indicate different voltages depending on what time of day it is, as the line voltage fluctuates. In a similar manner, your signal generator will drift as the line voltage fluctuates, to say nothing about the constant drifting of these cheapo devices with fluctuations in operating / ambient temperature. Cheap signal generators are very poorly shielded, which can cause one to lose sonfidence in the procedure very quickly.
Back in the '60s, I worked in a radio TV shop, just before the whole industry went to department stores, and the owner had Precision (brand) test gear. My stuff at the time was all Heathkit, so I was impressed. That was then, this is now, and I know better. I'm sure my boss would have used better stuff if he knew about it, and could afford it. Things are much different now. A lab grade signal generator that cost thousands of dollars in 1964 can now be had for $35. Seems to me to be a no-brainer. If someone wants to collect this cheap test gear, that's fine. Put it on the shelf, and dust it occasionally. If you are serious about your work, get some good tools.
My opinion is to buy the best you can afford, and true, what used to be outrageously expensive lab equipment is now available at a very modest price. You CAN use the older equipment, and as time goes on one will find what they can and can't do.
For example...I own 3 cars, and my favorite is my 1972 Dodge Dart. It's my favorite, and sure, back in the 70's we used to drive these all over and never gave it a second thought. But...this is 2005. For all its charm...well, you have to watch out for deep water because the brakes get wet, and the ignition gets wet. My 2004 Pontiac Vibe gets much better mileage and runs a lot better. With older cars you always had to monkey with something, the newer cars just run.
Old radios are the same...plain and simple you can just plug it in and it works, uses a lot less power too. No fragile, relatively short-lived tubes.
So we're kind of living a paradox, aren't we? Using better equipment and materials than were available when these sets were current.
If someone can get a great deal on the better equipment, do it! But I also wouldn't turn down an "offer you can't refuse" on a piece of equipment I don't have at all.
It's not just a radio, it's history you can use!
I've been frustrated lately trying to do alignments but I didn't want to blame my generator. I used to rely on a big old Hickok until a retiring tv repairman gave me his EICO. Since it was the newest of the many generators I have, and solid state, I trusted it completely. Now I realize this may have been a mistake!
The radio's we are aligning will probably drift more than the "cheap" test equipment we use. Some of this "cheap" stuff is actually pretty stable and accurate. If you can afford better test equipment, buy it, but don't think you need it to do a decent job on an antique radio.
Intelligence is the ability to use your knowledge
I think one of the pitfalls that happens all too often is not allowing time for the set and the signal generator to warm up and stabalize. If you have a frequency counter, you can constantly monitor the frequency and retune as necessary.
Also, I have harped on this before, but it needs repeating every time re-alignment questions seem to come up. Make sure that the set is completely dried out. Just bringing in a set from the garage or outbuilding and slapping a few new capacitors in it and then proceeding to attempt aligning it is bound to result in less than desired results. Let the set play for a week or two to drive all moisture out of the coils then proceed.
As for my choice of equipment to use, I do the simple thing. I use the best that is available to me at the time. Whether it is Hewlett-Packard, or Heathkit or Homebrew (the three H's). Knowing the limitations of each and working around those limitations is the key to success.