Dynaco FM3 Rebuild

[pro_crip]

Has anyone out there refurbed an old dynaco fm3? I just got one from the bay for next to nothing. After stripping it all the way down, it looks like a great candidate for a rebuild. It was a Cali tuner so there's no sign of rust on any of the chassis components, sure to change rapidly in the salt air of my coastal home. Due to some various problems I've read about it online, I decided to just strip out all the components and replace all the resistors and caps and what-not. There's even a re-designed motherboard out there that makes the wiring even easier than stock. Even the tuning cap looks to be in good nick. The only deficient area is tubes, it's missing a bunch. I've dropped a hint with the family about some of them NOS Telefunken EMM801's out there that would make a great holiday/b'day gift. The rest I can pick up on my own in drips and drabs, this project is at the bottom of the queue. I was planning on going all Tele on the tubes. Anyhoo, if someone else has travelled this path and wouldn't mind sharing some of your hard-worn knowledge, I would be appreciative. Thanks for listening.


Rich

[VoltSecond]

Unless you are buying a pre-aligned RF section, don't touch the RF.

I've done the mods in Audio Amateur and liked them.  A mod I wanted to do, but didn't get around to designing was to replace the rectifier tube with UF diodes, snubber, a soft start circuit and a CCS fed shunt regulator.  This should actually reduce the temperature of the FM3.

Note: NPO capacitors sound very good.  Calling NPO a "ceramic cap" is like calling a Teflon and foil cap a "plastic cap."

[pro_crip]

I was going to run an alignment procedure using the only fm station I listen to as the "low" frequency (89.5 FM, college metal) as per PJ's suggestion to optimize tuning for that freq. Excuse a newb, but what's a NPO cap? I've seen mod articles written in Glass and Valve, not anything (yet) in audio amateur. Trying to find free/low cost reprints of these articles as I've seen reprints for $20 out there. That power mod you mention sounds great, except I'd have no idea how to design it. Knowledge level hasn't progressed that far (yet) but then again I'm only a biologist, not an engineer ;P Thanks for listening.

p.s. I built your pseudo-dual mono power mod and snubber mod for my fp2, your site was fun reading

Rich

[howardnair]

i have salvaged 2 of them one being a partially built/unbuilt--so basically new--if the boards are good get the pec's and the power supply board from the fm3 zone and the led backlight module-and there is good info on the net about replacing some resisitors on the front board--on the older fm-3 i did not fool with  any parts in the radio section and was able to align it quite well using the dynaco manual-i did open the radio tuning capacitor and with a thin screwdriver apply white lithium grease to the bearings-i forget who told me to do this ,but it really cleared up the reception-better ground is what i recall -the pec's are a real improvement--go to the dynacotube audio forum baddog1946 can be found on page 2 of the basket he just rebuilt one with all new motherboard-also on that forum   ping gp49 or the curcio  forum gp49 or bill thomas--i love the sound of mine-musical is the term i would use

[VoltSecond]

An NPO cap (also known as COG ) is a class 1 ceramic capacitor who's
 
* Capacitance does not change much with temperature,
* Capacitance does not change with applied voltage
* Lacks microphones
* Low loss
* Low dielectric absorbtion
* Low Distortion

Example NPO cap
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BC1046CT-ND 

[Natural Sound]

This is a must read IMHO http://www.avahifi.com/index.php?option=com_content&view=article&id=185&Itemid=181

[Doc B.]

I've seen mod articles written in Glass and Valve, not anything (yet) in audio amateur. Trying to find free/low cost reprints of these articles as I've seen reprints for $20 out there.
Rich

Here are links to the VALVE articles, from the recently uploaded VALVE archive:

http://www.bottlehead.com/VALVEarchive/1998/va031998.pdf

http://www.bottlehead.com/VALVEarchive/1999/va011999.pdf

Classic Buddha dry wit from the second article:

"A better answer is my combination tube shield/microphonic attenuator. This process should be used on all tubes in the set, especially the RF-IF  tubes. Some folks might not like the sonics when this technique is used on the audio tubes because much of the reverb is lost..."

I sure miss that old geezer.

[pro_crip]

Voltsecond, I came across this guy's site http://www.quadesl.com/pdf/fm3_capboard.pdf. The art work for the board has spots for 2 diodes for solid state rectification. It also replaces the quad cap, which I hear is a good idea. I don't know if it'll make designing an upgraded power supply easier, but I thought you might want to use the info.


Rich