Several years ago I rebuilt/restored a Dynaco FM-3 with the singe board from the FM3Zone, it all looks OK, but it won't tune and only hear a faint sound. Anyone of have any interest in taking a look? I am willing to pay. I am not experienced with radio issues but have no way to tune first IF stage or determining if if other transformers are working correctly. I realize this has limited value but have already spent enough time and money and would like to see thsi through. '
Many thanks for looking
Many thanks for looking
Are you trying to do this without at least a RF signal generator or do you have equipment ?
The reason I am saying this as it isn't just a matter of getting a signal but distortion values relate to the correct tuning .
The reason I am saying this as it isn't just a matter of getting a signal but distortion values relate to the correct tuning .
The FM-3 kit was designed to be aligned without special test equipment. The tuning eye is used instead.
A DVM may be used for part of the alignment, making it a bit simpler. The results are quite good
in my experience, having owned and built a number of FM-3 tuners, starting since they were new.
One of my modified FM-3 tuners embarrassed a customer's Marantz 10B in sound quality, if not sensitivity.
http://www.tubes4hifi.com/Dynaco FM-3 manual.pdf
A DVM may be used for part of the alignment, making it a bit simpler. The results are quite good
in my experience, having owned and built a number of FM-3 tuners, starting since they were new.
One of my modified FM-3 tuners embarrassed a customer's Marantz 10B in sound quality, if not sensitivity.
http://www.tubes4hifi.com/Dynaco FM-3 manual.pdf
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I don't have an RF generator, yes I have tried to manually tune but the first IF transformer I suspect is also out of tune and need to be retuned with an 10.7 Mhz signal. This is, as I understand, the base for the rest of the tuning.
Your right Ericoto its 10.7 MHz but it doesn't need to be exactly on that .
You could attach some sort of indicator after the discriminator to watch any change but as you don't have a generator then plug in an aerial .
You could "peak it up " -IE just tune for the loudest signal at each stage not too accurate but its a start.
You could attach some sort of indicator after the discriminator to watch any change but as you don't have a generator then plug in an aerial .
You could "peak it up " -IE just tune for the loudest signal at each stage not too accurate but its a start.
They were supplied pre-set so that only minor adjustments were needed. Stewart Hegeman did a
very good job designing this tuner, and it works quite well when aligned as intended.
This should help if T1 has been misadjusted, from Bill Thomas.
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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An alternative would be to buy a different used T1 from dynacodesigns, which presumably would
be preadjusted. You could ask them about that.
be preadjusted. You could ask them about that.
Thanks all for the advise, I'm setting up to try again,. will pay close attention to the caps as well, not sure I was as careful before. Thanks also for info on adjusting T1, I really think that maybe an issue, I had read this before, but couldn't find again when I needed it. I also replaced 6AT8A, it tested subpar
The trimmer capacitors on top of the main tuning capacitor are extremely critical
for the tuner's effective sensitivity. Also use a plastic tool for those.
for the tuner's effective sensitivity. Also use a plastic tool for those.
Yet another, for the gear-rich, is to use a good-working tube FM tuner as 10.7 source. Tack insulated wire to the last IF plate, and throw it across the Dyna's tuner. Tune the source tuner to a station good as you can. Now peak the Dyna's trimmer (1st IF bottom?). Once that is real-close to 10.7MC (does not have to be exact, just within trim range), disconnect and unpower the temporary source tuner, then go through the rest of the Dyna trims.
You'd think you could buy a 10.7MHz oscillator.
This is a black box and a lot of money:
https://www.amazon.com/DSC6003MI2A-010-7000T-Oscillator-10-7MHz-Stability-Automotive/dp/B07V9ZSYRQ
Ahhhhhh that's a 25-pack. Mouser will sell you just one:
DSC6003MI2A-010.7000T
This does much more than we need but has a pretty face:
https://www.amazon.com/dp/B07G9GF8YL
There's a cheaper unit which does 35MHz to 4400MHz(!!). 42.8MHz and two flip-flop dividers?
Hi,
Just for your consideration attached it is a link of a 10.7 mhz oscillator schematic easy to built and parts that you can buy in Mouser store.
10.7 MHz Oscillator (ART043E)
Just for your consideration attached it is a link of a 10.7 mhz oscillator schematic easy to built and parts that you can buy in Mouser store.
10.7 MHz Oscillator (ART043E)