"New" Project

Sometime over a year ago I bought a pair of JBL monitors from a guy I work with who bought them brand new for his home recording studio many years ago. He always hated the way they sounded and he sold them to me in mint condition for $100. I bought them not because I wanted them, but because they were $100 and in mint shape and I knew they were worth more money. The rub was the speakers are big and heavy which means they are a pain in the ass to ship once they are sold because of course the original boxes are long gone.

I have a friend who is a hunter/gatherer of all things audio and I decided to trade him the mint JBLs for a pair of ancient Dynaco MKIII amps that looked like they had been stored in salt water and were originally built by Tommy Ten Thumbs many years ago. I figured the power and output transformers were worth more money than the pair of JBL speakers. I actually built a pair of monoblock amps from scratch based on the MKIII circuit many years ago and they actually sounded damn good. At the time, I used the Magnaquest replacement power and output transformers for the MKIII which I don't believe are made any longer. I have no idea if they are *better* than the original cloth covered lead transformers from Dyanco.

Anyway, I ordered new SS MKIII chassis replacements, the dual triode input boards (unstuffed) from Triode Electronics (I used these boards in my monoblocks that I built previously and know them to sound great), replacement chokes, new tube sockets, WBT binding posts and WBT input jacks, new hardware, terminal strips, the SDS Labs power supply boards, and the dual bias kit. Basically, everything will be brand new except for the power and output transformers when I'm finished. I figure they will make a good pair of backup amps and who knows, maybe they will see some time in my system. Below are some pictures I took of one of the amps before I tore it apart and trust me, the other one is just as hideous looking. Stay tuned for updates as they are brought back to life.

amirm said:

They sure are "crusty." Kudos for doing hand work like this. Will be rewarding when it produces audio!

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Amir-It will be rewarding as long as the power and output transformers work!

RogerD said:

Mark,

Now that's living,I love to do projects like that and with only 2 caps and maybe 16 resistors per amp the sky's the limit,have fun. Try a few TX2575 if there are any 1/2 watts and some tantalum resistors like Shinko or Audio Note 2 watt for those big ones.

http://www.negativland.com/dumb/blog/wp-content/uploads/2008/09/schematic-diagram.jpg

http://www.negativland.com/dumb/blog/?p=473

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Roger-There are a lot more than two caps. The input boards have a bunch and the power supply boards have a bunch as well. Aren't the Shinko resistors out of production and all people have left are some selected values and not all values?

rbbert said:

My first component stereo (in 1970); PAS 3, 2 MkIII's, Dyna A25 speakers, AR 'table w/ADC XLM cartridge. Enjoy yourself!

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Actually, for 1970, that was a pretty decent rig. Out of all the above components, I think the MKIII amps have withstood the test of time better although there are still people buying and using the PAS 3 preamp.

RogerD said:

Mark I noticed that after a closer look. Parts Connexion has everything.

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Roger-For the input boards, I need the following resistors:

(6) 470K 1/8 watt
(2) 10K 1/8 watt
(4) 10K 2 watt
(2) 47 ohm 1/4 watt
(4) 820 ohm 1/2 watt
(4)22K 2 watt
(2) 100K 1/2 watt
(4) 100K 1/4 watt
(2) 1.5K 1/2 watt
(2) 10K 1/2 watt

For the amp circuit I need the following:

(2) 1K 1/2 watt

What do you recommend?

whart said:

MEP- FWIW, i have a friend who is not an audiophile. Nada. Zero interest. And recently, he got intrigued by the whole vinyl/tubes/audio thing. He went out and bought some old Dyna gear, is now retro fitting it with better caps, upgrades, rectifier changes, etc. There are so many sources for Dyna parts, kits, mods, etc. I just skimmed the surface on what's out there. (I built an ST-70 kit back in the day, and shockingly, it worked!)
Somewhere, i read that the 'factory built' units were actually assembled by part-time workers from a local college, dunno if that's true.
My buddy is having a ball- I consider him a capable guy, but not somebody with any background in electronics, as you have, and he's really into it now! (I gave him a bunch of vinyl which helped me make room for the organization of my collection, so it has been a blessing for me too- he's also building a homemade vinyl cleaning system, and cooking up home brew cleaning solutions). I don't expect him to go Walter White on me, since he is a part-time cop.

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Bill-Dynaco sold more MKIII amps than all of the gear combined that some modern day audio companies have ever sold. That is why there is still such a big aftermarket for Dynaco tube gear. There is literally tons of Dynaco gear still in use and in the case of the MKIII, they actually sound pretty damn good. With modern day parts and power supply upgrades, they can even sound better than they originally did. It's hard to believe that they sold as kits for $79 and that included a pair of British KT-88 tubes and usually a Mullard GZ-34. Too bad we can't climb into a time machine and go back and lay in huge supplies of killer tubes for peanuts.

I'm glad I still have my tube collection. My input boards use a 12AU7 and a 12BH7 and I have a killer collection of 12AU7 variant tubes. I pretty much have all of the usual suspects and I have some really good NOS American made 12BH7 tubes. I also still have some Mullard GZ-34 rectifiers.

John-Thanks for the kind offer, I appreciate it.

RogerD said:

Mark, let me take a look and I will PM you.

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Thanks Roger.