• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Dynaco Mark III

I don't know much about tube amps, but I'd like to build a Dynaco Mark III amplifier to familiarize myself with them, to see how it sounds, and because it's fairly powerful. Does anyone know anything about this amp?

here's a schematic: http://www.tanker.se/lidstrom/mark3.gif

I'm thinking about bi-amping this amp with a 300W solid state AB amp that I'm building. The tube amp would be used for the midrange and highs. I hear that tube amps are best at midrange.

[Edited by Kilowatt on 12-09-2001 at 03:16 AM]

I have owned many Dynaco amps and preamps. Several years ago I sold my MKIII's after hearing an ST-70. The MKIII was a very good sounding amp for what I paid for it. About $600.00 on the used market. Bass was solid and fairly tight for a tube amp. Midrange was excellent using Svetlana 6550 B3 or 6550C's. I also had GE nos 6550's which were very good in it. Highs were fairly smooth and clean. It threw a nice wide soundstage, with great detail.
The st-70's midrange,(where 90% of all music exists), is much, much better in my opinion. It is almost holographic, or 3d in nature, while the MKIII's mids sound more like a very good,(expensive), solid state amps. The drawback is the 35 watts per channel in a st-70 vs 60 watts for the MKIII. With the right speakers, the ST-70 is superior in my opinion. I have used them with 90 db sats/subs, Magnepans, and Klipsch Lascala horns. The Magnepans sounded glorious at low volume levels. The Klipsch horns rocked the house with the ST-70.
That said, the MKIII is a fine amp if you need 60 wpc. There are tons of improvement mods on the net that make it even better. If you are looking for transformers for your project, here is a link for brand new power and output trannies for Dynaco MKIII's and ST-70's. These are built exactly to the original Dynaco specs. They are a little pricey though. Ebay has lots of used MKIII parts for sale at decent prices also.
LINK: http://store.yahoo.com/triodeel/magnequest.html
Best of luck with your project. Let us know how it comes out!
Well, right now I don't know exactly how much power I'm going to need. I'm going to have 500W (250W/channel, solid state of course) for below 250Hz. That'll be 40% of the total SPL. The sensitivity of that system is 95dB/[email protected] I don't know what good and reasonable priced midrange/high speakers I'll use for the tube amp, or where I'd get them, I haven't come acoss any on the internet, but when I do, I'll be able to figure out how much power I'll need for it. It's stereo, so I may find that the little ST-70 will work just fine. Any suggestions on what speakers to use for mid/high?

This is not really related to this thread in particular but this is as good a place as any.

What exactly are you building?

You have asked many reasonably extreme questions relating to completely different topics across the forums here saying you are building many different projects.

Could you please clarify this as I, for one, am getting the feeling that you are beginning to waste our time as was noted in the thread on your 1.8kW amps.
Hell no, I'm not wasting your time. I'm building a system that will have a 2 x 250-400W or so bass amp (that's in a thread in SS called "400W amp project") and a 2 channel tube amp for mid and high frequencies. That's what I'm doing. I asked about hybrid amps just because I was curious. I guess we don't have to worry about the 1800W amps, I might pick that project up again much later when I have more experience, or if I can find something with detailed plans. I'm asking about the MOT supply in an attempt to save money on the tube amp.

I'm getting the impression that people on these forums aren't finding it easy to put up with me, I must be getting annoying. Sorry about that, that's just kind of how I am.

[Edited by Kilowatt on 12-09-2001 at 06:26 PM]
Speakers for tube amp.

There are many good mini sattelites that would work great with an ST-70. Since your low end is taken care of, you would only need a 2 way sattelite with decent response down to 100 hz. or so. Where is your bi-amp crossover point between the subs and mid/high systems?
I got great results with the following set-up:
Pair of homebuilt subs using NHT 1259 12" woofers in 2.5 ft^3 heavily braced enclosures, driven by Adcom 555 II's.
Gave about 300 watts per channel as 1259's are 4 ohm.
Pair of Dynaudio MDY-3 sattelitte kits from Madisound, driven by Dynaco ST-70. The MDY-3 uses Dynaudio's 6.5 " woofer and D-28 tweeter in a triangular shaped enclosure.
Madisound has the newer version at there web site for about $600.00 in kit-form.
Marchand XM-1 electronic xover boards. 24 db/oct. at 200 hz.
Op-amps changed to Analog Devices AD712's, and polysttyrene caps replaced with equivalent value polypropolynes by Xicon.
Power supply was +/- 15 vdc Walt Jung / Gary Galo design using Linear Technology regulators.
This is shown as PS-1 at Welborne labs web-site.
Just one idea.
Thanks, well I think I'll look around for speakers, Dynaudio is very expensive, they seem to me like they're the Cadillac of the audio world. Anyway, I think I shall get this project underway. Sometimes I have multiple projects going on at once, and it often takes me forever to get things done, but I get by. I'll probably end up building an ST-70.
Heh heh, kilowatt is a cool moniker..

My advice FWIW it's worth would be to not build a Mk III, firstly because the driver circuit is commonly upgraded anyway, and secondly because 6550s are expensive. Instead I would suggest the Eico HF-89 circuit which will get you about 50 watts/ch from EL34s. I have one with Hammond 1650R output transformers, sounds good.

If you want high power, check out the Super-Compact 150 amp in the book Audio Reality. However I wouldn't recommend that to beginners because of the high supply voltage.

I think the Poseidon boards look pretty sharp, too.

By the way, if you like the Poseidon, Shannon also makes a board for the Stereo 70 with essentially the same topology. It's just two Poseidons stuck together in the middle (or is the Poseidon one of his ST70 boards cut in half?).

Can someone explain to me the advantage or difference of the Poseidon Board over the stock driver board? There is so much information its hard to find the relevant information. I am looking at building the MK3 and my main concern at this point is that my speakers have a frequency range of 20Hz to 25KHz and I don't want the highs to sound rolled off. Which of the mod driver boards would best suit my needs? What about the Bob Latino Board?
Does anybody have a link to where Shannon Parks first released his circuit design on DIYTube?

The Stereo 70 driver board seems to have been announced first, roughly around the beginning of 2005. The post is here:

diytube.com • View topic - diytube st70 driver board

Curiously, even though his post states the prototype circuit was first tested as a "1/2 unit" running in a Mark III, the Poseidon boards weren't announced until a little over a year later.

If you really want to dig into the history of the Parks projects, I believe the DIY Stereo 35 came first. After that, the Eiclone was conceived (mid 2003). I would imagine the Poseidon circuit and ST70 drivers were simply a natural evolution of the Eiclone design (sans power supply and finals). Have a read through the oldest of the posts in the Eiclone forum for more details.
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