Dynaco FM-3 Upgrade Pictorial

Thanks for looking anyway Gary. I know first hand what it's like to try to find something when you want to. If you're like me, stop looking for it, then you'll trip over it.:thmbsp:
 
I was wanting to see the schematic with the mods in place.
Very little changes, really. The filter capacitor bank constitutes a different deal altogether, but still, at the ass end, the equivalents of the sections in the original get wired to the usual suspects on the chassis. Then there is that thingy-puffer that increases sensitivity — I can't speak to that. I can speak to the PEC board substitutes. I made my own and used the schematic illustrated in Sheldon Stokes' web site. This concerns small boards upon which discrete resistors and caps are mounted. These made a very big improvement. BTW: I used polystyrene instead of silver mica caps, but I recommend the latter over the former.

I also wired up my own cap board. But, about the same time that I got further involved in rewiring some of the old circuit, I got distracted by a Sony ST-5150-D. I recapped the Sony, and it turned out to be so flaming good that I've still got the FM-3 in pieces. The Sony is currently doing service.

I have heard the results of my PEC substitutions in combination with a number of fresh film capacitors. Prior to these mods, the unit was aligned by a pro using a signal generator and altered to the Japanese bandwidth. Verdict: it's very worthwhile to do these simple things — in conjunction with an alignment. Caution: a new cap board or can may make a realignment necessary.

I made some drawings related to some of the work I did. If you are interested in copies, please send me a PM.
 
Lorne- what improvements did you note when you replaced the PEC circuit? Also, I would like to inform some of you how important it is to align the Front End of the FM3. I was receiving static every time I touched the tuning dial so I thought I would clean the tuner (following the tuner cleaning steps outlined in the "Tuner Forum" of the AK site.) It made no noticeable improvements that I could tell. So now I was becoming worried that something more serious was at play. Not knowing where to start I jumped in at that section (Front End Alignment) of the Dyna manual. After performing the steps the tuner is now static free I'm glad to report. I have not rehooked the tuner to my main system with the out door antenna so as far as sensitivity be helped I can not say. But I will be back shortly to let you all know of it's performance in this capacity as well. EDIT: Yes it also helped in the sensitivity of the tuner as well, good luck and enjoy.
 
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Lorne- what improvements did you note when you replaced the PEC circuit?
Sonics ... more articulate and euphonic. I will not say that it improved anything but the sound itself. I can't remember enough about what the PEC does in the circuit, but a faint memory points towards this making sense — in regards to sound that is. Other parameters are IMHO unaffected.

Making my own was a real PITA. It seemed simple enough before I started, but working on breadboard using 30 gauge wire in such a tiny space was awful. You have to keep heat away from polystyrene caps. I used epoxy to seal out O2 from the bare copper wire I was using. I followed the schematic found on Sheldon Stokes' site — literally. The lay-out and wiring was a direct reiteration. Despite the improvement in sound, I'd not do it again. Buy the new boards from FM-3 zone!

Of course, if burning boards is a ho-hum exercise for you, the artwork is there on Sheldon's site — or maybe he is selling the bare boards. I chose to build them 'cuz I had these styrol caps around. But the problem is that they end up being too close to the rectifier tube — which gets scalding hot. very unhealthy for polystyrene caps. I may be in the market for new boards myself. Check: I would not consider an FM-3 without discrete boards in the future. It made a difference in sound that I really appreciate.
 
I have a FM-3 and SCA-35 and their biggest problem is that they were built on a chassis about half the size as should have been used for heat dissipation. Yes, large enough to build the kit but poor engineering. These 2 units literally seem to cook themselves to death.
 
I have a FM-3 and SCA-35 and their biggest problem is that they were built on a chassis about half the size as should have been used for heat dissipation. Yes, large enough to build the kit but poor engineering. These 2 units literally seem to cook themselves to death.

A small muffin fan will cool them down plenty to sane levels.

Russellc
 
I keep the covers off and plenty of room for circulation and have a set of fans in a frame that I've used on the SCA. However, these compensate for a poor design decision and hence a bad design and not a cure for the design itself. I've considered going to a 2-chassis design of the 35 as part of a makeover but I just hate ripping apart a classic.
 
The Japanese tube pro who aligned my FM-3 and checked out the boards a few years ago gave me some advice when he handed the unit back to me. Leave the cover off, he said. In the summer, you mean? I replied. All year, he answered.

BTW, the same guy altered my FM-3 to receive the Japanese bandwidth.
 
I have a FM-3 and SCA-35 and their biggest problem is that they were built on a chassis about half the size as should have been used for heat dissipation.
Perhaps the majority of Dynaco products were distributed in the mails. The idea must have been to keep the respective chassis models down to a minimal size in order to facilitate economy in shipping. Everything about the Dynaco idea was to popularize effective audio on a mass, affordable scale through a skillful balancing of shrewd engineering and frugal economics. The result was not totally effective nor was it expected to see these things into brilliant operation 45 years later. The fact that so many of them continue to work as well as they do is something to consider.
 
Sonics ... more articulate and euphonic. I will not say that it improved anything but the sound itself. I can't remember enough about what the PEC does in the circuit, but a faint memory points towards this making sense — in regards to sound that is. Other parameters are IMHO unaffected. <snip>

The PECs under discussion here do indeed affect the sound directly and possibly other things more subtly. Specifically, the PECs implement the de-emphasis curve and filter out a portion of the 19 KHz and 38 KHz pilot and subcarrier signals and other ultrasonic junk. The original PECs contained wrong component values so the de-emphasis curve was incorrectly implemented causing non-flat frequency response. The revised network corrects this and provides better rejection of pilot and subcarrier. The latter two items can interact in subtle ways with some amps introducing added distortion at lower frequencies. Note too that the original PECs are suspected to contain ceramic caps and carbon comp resistors...maybe not so good sounding in and of themselves even if the nominal component values had been correct.

For the record, sussing out the FM3 PECs was originally done by David Berning and published in the letters section to Audio Amateur ...yeah, it's that old.
 
After surviving the Midwest AK fest this weekend, I tackled a few of the easier mods from the kit today.

First up is the replacing of the flacelight bulb with an LED. Had to move one resistor from top to bottom and mount the LED board.

Before shots:

FM3LightB4.jpg

FM3LightB4Back.jpg

After. These picks don't do this mod justice. It is a more defined light source than the blasting bulb. Very cool looks.

FM3LightAfter.jpg

FM3LightAfterBack.jpg


Next is the Selectivity/Sensitivity Module. Easy no solder upgrade. The S/S Module increases the tuner's ability to recieve distant stations without being squashed by closer, stronger ones. I now must do the alignment so it may slow me down a bit.

Before

SSModB4.jpg

After

SSModAfter.jpg


So far darn easy. Lets hope I don't get lost somewhere down the line. Let me know if you have any questions.

Gary

Hi Gary
I know this is a 10 yr old post but i was wondering if you can still help me out.
i'm looking for the value of the capacitor used for the selectivity/sensitivity mod.

thanx
 
I had fm3 zone make me a custom face plate for the PAS I built. A repop chassis, ph-10 phono, Aikido line stage and the SS dual PS. When I do my fm3 ill have him do a face plate for it as well. I want to use a rotory power switch instead of the factory type used on the fm3. 20161004_092041.jpg20161004_092057.jpg
 
After surviving the Midwest AK fest this weekend, I tackled a few of the easier mods from the kit today.

First up is the replacing of the flacelight bulb with an LED. Had to move one resistor from top to bottom and mount the LED board.

Before shots:

FM3LightB4.jpg

FM3LightB4Back.jpg

After. These picks don't do this mod justice. It is a more defined light source than the blasting bulb. Very cool looks.

FM3LightAfter.jpg

FM3LightAfterBack.jpg


Next is the Selectivity/Sensitivity Module. Easy no solder upgrade. The S/S Module increases the tuner's ability to recieve distant stations without being squashed by closer, stronger ones. I now must do the alignment so it may slow me down a bit.

Before

SSModB4.jpg

After

SSModAfter.jpg


So far darn easy. Lets hope I don't get lost somewhere down the line. Let me know if you have any questions.

Gary
Hi, I'm looking for this selectivity/sensitivity modification part but cant find anywhere.. anyway you can read me the code on the ceramic filter itself? It would really help. Thanks.
 
I've always liked the FM3.

Really nice suite of mods gets me thinking.................
Had an FM-3 at work, in a desk drawer with two LM386 amplifiers, two 6V lantern batteries, and Koss Pro-4 AA headphones. The site was high on a mountain ridge a few miles from the Pacific Ocean, not quite halfway between L.A. and San Francisco, so reception was excellent.

Antenna was an el cheapo FM turnstile mounted in an unused radome, feeding about 100 feet of RG-59 with a cable TV 1:4 balun at the tuner.

Thank goodness for the signal capture ratio characteristics of the FM format, as there were seemingly unlimited stations available.

The Dyna tuner left nothing to be desired in sensitivity, selectivity, or sound quality. In 1977-79 a fair number of FM stations still transmitted high quality signal programming. Take away that and the near ideal receiving location, I not sure how it would perform today as a truly HiFi source.

Another piece of gear I wish I hadn't sold. If only I...
 
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