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Old 9th December 2001, 06:01 AM   #1
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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]
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Old 9th December 2001, 08:22 PM   #2
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Default Dynaco MKIII SCRATCH BUILD

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!
mg16
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Old 9th December 2001, 09:24 PM   #3
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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/W@1m. 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?
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Old 9th December 2001, 10:26 PM   #4
jduncan is offline jduncan  United States
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Kilowatt:

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.

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Old 9th December 2001, 11:24 PM   #5
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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]
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Old 10th December 2001, 12:34 AM   #6
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Default 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.
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Old 10th December 2001, 03:32 AM   #7
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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.
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Old 10th December 2001, 05:37 AM   #8
jduncan is offline jduncan  United States
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Kilowatt:

OK, thanks for clarifying that. With all your different posts it sometimes comes across as though you really have no idea what you actually want to build.

Thanks again for the clarification.
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Old 10th December 2001, 08:13 AM   #9
JohnR is offline JohnR  Australia
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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.

JohnR
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Old 27th July 2008, 08:54 PM   #10
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anybody ever add a second set of output tubes to the mark III, build monos on the same chasis and bridge them in series, build mono's on the same chasis and parallel wire?
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