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 Post subject: Dynaco FM3 Alignment
PostPosted: Dec Mon 27, 2010 5:24 am 
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While I am well versed in AM radio alignment FM has always been outside my skillset and equipment base. Still is.

Now, the Dyna company and their kit based radio was probably unique, in that it was designed and built to be aligned by the builder utilizing the EMM-801 eye-tube and little else in the way of conventional test equipment. A VTVM is helpful, but not necessary.

BUT, all of the steps (at least in the IF strip) are predicated on at least the initial 10.7 mHz IF alignment being pre-aligned at the factory, correct? I guess this might be T-4, the very first transformer adjustment in the procedure?? The instructions even stress that their particular alignment procedure cannot be improved upon and, that conventional sweep alignment should not be used.

If my thinking is correct, though, then all the other adjustments are only aligning to whatever the intial IF value is. So is there a good way, (or even a bad way) to check/verify this with basic gear outside of oscilloscopes and modern test gear like frequency counters?
While I expect this radio to be "close" based upon its performance it is also true that a GOOD alignment makes all the difference.


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 Post subject:
PostPosted: Dec Mon 27, 2010 11:42 am 
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Actually, the transformer that should be "pre-aligned" to 10.7 MHz is the Bottom of T1, the IF transformer located on the RF board. Here's a simple way to do it:

1. Remove V2 - 6AT8A and apply a 10.7 MHz signal through a 100 pF capacitor connected to pin 6 of the 6AT8A socket. (Caution: when the tuner is on there will be around 220 Volts on this pin!)

2. Warm up the tuner and the signal generator for awhile.

3. *Gradually* increase the signal generator's Output Level from Zero until the bottom section of the EMM801 starts to close.

4. Using the proper plastic alignment tool, adjust the Bottom slug of T1 for maximum closure of the EMM801. If the eye closes completely, back off the signal generator until a peak can be easily observed.

5. Power everything down, remove the signal generator connection, replace the 6AT8A and perform the normal alignment. However; if your dial-tracking is correct, do NOT perform Step 3 on page 16 or Steps 26 through 28 on page 18.

6. The idea is to align the Primary of the First IF transformer, THEN go to the last tuned circuit in the IF chain and work backwards to the TOP of T1 - the Secondary. Since the Primary is already set to 10.7 MHz, don't adjust the bottom of T1 again, but it wouldn't hurt to perform a second pass from the top of T4 back to the top of T1.

The only equipment you really need is a calibrated signal generator, or a non-calibrated one and a calibrated frequency counter. (Actually, calibrated counter is nice, but a garden-variety frequency counter will *probably* be "good enough.")

There are really only three "touchy" areas when aligning an FM-3: The oscillator adjustments for dial tracking; the discriminator adjustment; and the alignment of the multiplex board - especially the adjustment of T73 which is VERY touchy and absolutely CRITICAL for good stereo performance and separation.

Using the "tuning eye" method of alignment will ABSOLUTELY perform as well as using a VTVM (or similar high Input Impedance meter).

Hope this helps.

Bill Thomas


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PostPosted: Dec Mon 27, 2010 1:36 pm 
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BILL: Thank you! _Exactly_ what I was looking for. Still digesting it.

I have a signal generator, but no counter - but a digital readout SW?

A semi related question - are the multi-plex and discriminator alignments predicated upon an accurate IF strip alignment to begin with, or are they independent of this? That is, should the IF be subsequently aligned exactly to 10.7 mHz, does it necessarily follow that the discriminator and multiplex circuits are now out?

Thanks again for your help!


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 Post subject:
PostPosted: Dec Thu 30, 2010 6:04 am 
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Hi, Ted.

Sorry for the delay in responding. I've been dealing with a fried computer for a few days.

The basic alignment steps go this way:

1. Peak the IF's.
2. Perform the discriminator alignment.
3. Perform the *necessary* alignment to the RF board.
4. Perform the multiplex board alignment.

The Quality of the IF alignment has little effect on the multiplex board alignment, but the Discriminator alignment is VERY important. The better the discriminator alignment, the lower the distortion - both Stereo AND Mono.

I know you are approaching this with a good deal of caution, but you will find that a complete alignment can be performed in about 1/2 hour or less, once you get the hang of it.

If any of the tuning slugs are "frozen" in the cores, avoid using excessive force. If this happens, come back here and we can discuss possible solutions. It doesn't happen THAT often, but it *occasionally* happens.

Alignment of T73 on the multiplex board is probably the most "touchy" and critical part of the whole process. Small movement of the slugs can kill the Stereo, or even cause the channels to be reversed! Just follow the directions in the manual and you'll be just FINE!

Let us know how it goes and how it sounds when you're done, OK?

Hope this helps.

Bill Thomas


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 Post subject:
PostPosted: Dec Thu 30, 2010 1:01 pm 
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Hi Bill

Well the entire alignment procedure isn't new to me, have done this a few times, but have never checked that the IF is _exactly_ 10.7 mHz, just always used the tuning eye as outlined in the manual. But thought I could drag out the Triumph 110 siggie and let it warm up for a day or two, and bounce a signal off 10.7 indicated off a digital SW (poor mans freq. counter?)

My intention was to go through the entire alignment steps, especially if IF was off. Guess I'm a little unclear why aligning the bottom slug of T1 _only_?

I understand that alignment of the cores is always done in "reverse",
so does this initial "prealignment" affect the other cores peaks when using the tuning eye method?


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 Post subject:
PostPosted: Dec Thu 30, 2010 6:46 pm 
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The idea is to pre-align the Primary of the first 10.7 MHz IF transformer, then peak the rest of the IF cores to that 10.7 reference. As you surmised, setting the first transformer's primary will insure that you align the rest of the chain to that initial reference - working backwards from the Discriminator to the Secondary of the 1st IF. If the Primary of the 1st IF were set to 10.4 MHz, then the rest of the IF transformers would also be peaked at 10.4 MHz.

Using a communications receiver is a perfectly acceptable solution to "reading out" the 10.7 MHz signal.

Hope this helps.

Bill


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 Post subject:
PostPosted: Dec Fri 31, 2010 3:49 am 
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Hi Bill

Thanks again for explaining that. The manual points out that alignment is a "semipermanent" adjustment, but also allows that tube replacement would require re-alignment, but doesn't explain any further.

I can sort of figure that eventual replacement of the IF tube types
for example, 6BA6 and 6AU6 would affect the IF, and 6AT8?

6BL8 maybe the multiplex alignment? On the other hand 12AX7 at the audio output replacement shouldn't require any adjustments.

Do you have any suggestions or advice here, I did replace and/or lay in a stock of the tubes required, iirc you mentioned 6AT8 is run hard and tend to wear out first.

So far have replaced the power supply electrolytics, the larger value film coupling capacitors, those two undersized resistors, and the three
FM de-emphasis couplate deals. As of now tracking seems real good, and good sensitivity, and reasonable selectivity, There are a couple strong locals adjacent channels that can be used as a kind of test, but I could see where in a crowded big city environment with lots of stations the FM3 might run into trouble.

But this is a fine sounding tuner and it's just plain a lot of fun!!

This weekend will try to start out fresh with the alignment and see how it goes.


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PostPosted: Jan Sun 02, 2011 9:25 pm 
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Bill,

Ok, I was able to feed a 10.7 MHz signal into T-1 and peak the bottom core. Then went back and aligned according to the manual.
This made a tremendous difference, particularly on the second pass through, it's neat to see how the other cores slave off the first.

The C8 and L4 adjustments for tracking went fine as did the rest of the front end, trimmers B and D on the tuning cap.

The discriminator adjustment (VTVM is the way to go here) was as I remembered but more "touchy" as you mentioned. One thing people need to remember, be sure to remove the gimmick capacitor prior to discriminator alignment, and reinstall.

The Multi-Plex part is a bit of a pain but as you mentioned KEY to good stereo separation, in that the FM3 excels. Here's where I wish I had a pair of headphones, but as a "temporary" experiment last night was able to adjust transformers T71, T72, and T73 to a rough mechanical alignment as suggested in the manual, and then adjust "by ear" through the speakers. it sounded quite good.

Today I went through the Multi-Plex alignment portion "by the book" with the test points and 1.2 meg resistor. As you alluded to, T73 is the tough one, and can't be neglected. Thanks for your help, getting the IF spot on makes all the difference!

Ted


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 Post subject:
PostPosted: Jan Tue 04, 2011 1:12 am 
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THIS is the sort of outcome I LOVE to hear about! I'm REALLY happy it all went well, but to be honest, it isn't really surprising. First off, we're dealing with a pretty sharp "tweaker/aligner" here! (After all, you DID select a Dynaco FM-3, right?) But we're also dealing with a truly inspired bit of design here. While there were quite a few "kits" available back when the REAL Dynaco walked the face of the Earth, there weren't many that could boast "a complete alignment with NO test equipment necessary!" By pre-tuning that ONE transformer slug, the rest goes SO smoothly!

Now the fun part! Listening!

GREAT work, Ted!

Bill

P.S. I did a rather extensive rebuild of an FM-3 a while back and profiled the build at another website. (Their picture hosting is a bit more "full-featured" than here.) If you'd like to see what happened, click on the link below.

http://www.audiocircle.com/index.php?topic=69309.0

Bill


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 Post subject:
PostPosted: Jan Tue 04, 2011 2:21 am 
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Well I got up early that day ready to tackle the Multi-Plex "by the book". When I was done I spent the rest of the day listening to our local classical NPR station, and a program called the Folktree. It sounded so nice that it was fun to anticipate what they would play next. One song/artist in particular that I've never heard, was called "Anton" by John McSherry, a kind of Irish or Celtic piece that has some nice acoustic guitar that I always enjoy, but the sonics on that audio recording was amazing!

One thing I noticed today that is very gratifying, after this alignment there isn't any drift upon a cold start - turn it on, and there it is, dead on where I left it.

Thanks again Bill you have been a great help in many forums and have devoured the Fm3 stuff I can find on the web. I should also thank Chauncy at the FM3 Zone for providing the PEC replacements and other FM3 survival items, Joe Curcio at avahifi et.al, and of course the fine folks at this site. Bill - you should put together a page on FM3 alignment in the same vein as your restoration, it would be well received. (ba da bing!)


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