It's official-- there's a new tube convert in the world...

Tubes

Congratulations

Why use a Solid State amp with "tube like" sound when you can have the real thing? A tube amp with tube sound . Your ears will thank you.

As for mods, I leave my vintage Scott and Heath amps stock except for the output capacitors and selinium rectifier which must be updated for safety. Tubes are replaced if they are noisey or hum.

There are websites, user groups and forums for most of the manufacturers. They are excellent resources for all your questions on mods.

Happy Listening

 

Congratulations, Joel, and welcome to the club!

I was in a similar situation a couple of years back. I bought two McIntosh MC30s at an estate sale, and asked the same questions as you just did in a few forums. "My Macs need to be refurbished! Should I upgrade them, or just replace faulty parts with standard replacements?"

Several people on audioasylum told me how to hot-rod the amps, to squeeze more watts out of them and change the character of the sound. But I kept them stock, and absolutely love them. And I'm sure your Dynacos aren't that much different in this regard.

Well, I am no electrician, but I am fortunate enough to know a very good repair shop in Austin, TX, run by a fellow who owns MC30s himself. I paid him to refurb the amps, and he didn't do anything fancy. And I'm glad he did it that way. I had some cap cans and capacitors replaced, new power cords installed, and I love how they sound. I especially like knowing they've been repaired the way McIntosh thinks they should be. That peace of mind is worth a lot to me. I'm sure my Macs will run perfectly for another 50 years.

The easiest way to make them sound better, I've found, is using the right tubes. Tube rolling is much easier, and less dangerous (for me), than replacing the internals.

 

Stereo 70

I have heard that the Dynaco Stereo 70 is one of the truly great-sounding bargains of the century - congratulations. Let us know how it sounds when you get it up and running. I never had one. Not sure how I missed out on that, but it's a little late b/c I have too much stuff now.

 

I have a convergent audio tube preamp and just love it. I am waiting for the day when I can afford the power amps. I think tubes are the best way to go.

 

You haven't heard something "musical" in Hi-Fi Tube Amplification until you own and use a Dynaco St-70. I still judge the sound of most McIntosh, Scott and Heath vintage amps against both of my ST-70's. I'm not saying the St70 is better against any general amp, I just use it as a benchmark sound. If I hear something better, then I'll know immediately.

Yes, it's true; the amp does chew lots of voltage, and holds nothing back in terms of sound. It's not the most obtainable amp on eBay since people are starting to keep them, mod them, and love them more and more as time goes on. I'm sure just what I've said in AudioAsylum and here has made at least two people seriously look at Dynies. Most Dynaco's are already modded or wholly trashed. A few forum members asked me about their hunting on eBay. I know of two that almost bought a poorly-kept amp. Them's hard to find, them good ones! Modding is making a lot of sweeter Dynies extinct in their original sound!

About modding: IMO, the St70 IS a slllightly dark sounding amp, by just a tad. It has a range of warmth and detail with incredible midrange bloom. If it's wired properly with a great set of Mullards, music comes out of nothing, effortlessly, as if you've let your speakers flow from an etherial source. I was listening to "Days Of Furture Passed" and the melotron sounds of "Dawn Is A Feeling" seems to pour out as if the sound was always waiting to come forth.

Ok, ok, enough.

The dark, buttery sound IS desireable because of the vintage capacitors most of the original boards have, the Triad-Can cap, and the strength of the 7199 tubes. These, as well as using other tubes (Russian and other EL-34's) will make this amp change personality immediately. A guitar engineer for Jimi Hendrix said once; (from memory) "I had a fuzz box that Jimi wanted to use, so I gave it to him. He plugged in and hated it immediately. He made me switch distortion pedals 7 times until I went back to the original one. 'PERFECT - That's it!' He said, and off he went, using the same box he had in the first place."

My thoughts exactly after playing with these voltage beasts.

Think too, that many people are following many brave suggestions to mod them, mostly for fun and feeling of accomplishment. Many people modding an ST70 aren't doing it because they're running away MADLY from the original sound, they want to know how things sound when they royally screw with it. The vintage sound is what people heard on efficiant, simple speakers. You WILL find speakers that simple and efficiant, but you will find it hard that an amp will drive them as honestly.

That being said, I own a modded one, with the replacement driver board; the Soundvalves one with the 6GH8 driver twins found in some Scott amps. The midrange tightened up, and the amp got fast. Sudden sounds like snare drums and fast bass were coming forth like quicksilver. I lost the natural tones in the vocals and the smoothless of long bass sustain was cut a little as compared to my unmodded ST-70 with mostly Mullards.

Very true. A Dynaco ST-70 is a bargain even still. It's even better if you have some electronic knowledge and know where to get good replacement parts and tubes. Amps that do the similar performance go for $1200 or more today, if you can find something that sounds close!

Driver boards, can caps, and even some BlackCat caps used in the Dynacos are found here and there. A Dynie is well performed with care, and not everyone should own a tube amp.

I was curious. Then I bought one, then another. My plans were to sell them once I got the enjoyment out of them. They're more loveable than pet cats now. I can't see myself letting them go, knowing the care I put into them. Snif, Snif.

 

Replace the caps? Hogwash. Old and unsafe? Well, not normally. Unless this was a rotting, poorly kept Dynie, nah. Those caps will out-live even you and I, my friend. So far, I'm using the original can caps on each of my 2, and I DO have a SDS Labs replacement I built, standing by, just in case. I got a feeling I'll never use it.

Resoldering the driver board (pulling parts off too) isn't hard. You just need to make sure you don't break the fragile routed strips on the board. They will peel off. These PCB's are over 30 years old! Never pull components off hasty. Be very gentle, and you CAN pull things off the driver board if you WANT. If the driver board seems OK from your perspective (check all caps with a volt meter, all connections too) and you'll be suprised. Again, I don't know why one would just replace the caps. Replacing the whole driver board, all with linear-types of caps in the circut, is much better. People on eBay sell really good driver boards for upgrades as well as originals. It's not expensive at ALL.

Yes, get it working strongly with as little upgrading as possible. If you don't like something, well then go for it, but the sound of an original Dynaco is more desireable, and WILL be to most audiophiles. Get used to enjoying it rather than planning to rip it apart. Leave it alone for 1-2 years. THEN ask yourself, do I wanna?

One of the reason I have two, The original one is the oldest one and has mostly original tubes, caps and trannys. Since I bought the second one as modded, I can really do wacky things to it and not feel guilty for polluting it with mods.

**Sckott sez: As always, please be careful when getting into tube amplifiers; they capacitate and use lots of voltage. One wrong move and you could be hurt badly, or even killed. Always seek professional help if you are not confident in learning and/or electronic circuts. Respect electricity.

 

Check out the May issue of Stereophile, Fremer uses a Dynaco Stereo 70 in his review of Odeon horn speakers.

 

I just bought a Dynaco system, too!

Wow! I picked up a system with these three components two days ago. They need a little TLC and cleanup, but I might just build a backup system with them (I doubt if they'll match my McIntosh MC30s but I can't wait to find out).

Does anybody know a good source for stock replacement parts for these Dynaco components -- like power transformers and whatnot? And are the Dynaco components the same as the Dynakit components?

 

Dynaco = Dynakit; in the good old days you could buy Dynas factory assembled (Dynaco), or as a kit (Dynakit) when tubes ruled the roost. For a little while (I think) the transistor stuff came the same way, but then later the faceplates all said Dynaco regardless of who did the construction. Parts? Ebay is a good source - look for lowtechelec on Ebay - he has lotsa stripped Dynaco goodies available...