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Old 23rd January 2012, 11:25 AM   #1
ElCid79 is offline ElCid79  United States
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Default What are your opinions of the ST-70 and St-120

Hello. Title says it all. Tubes4hifi.com makes an interesting st-70 kit ans ST-120 kit. What are your thoughts?

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Old 23rd January 2012, 11:34 AM   #2
ElCid79 is offline ElCid79  United States
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And while we are at it let throw in the m125 mono blocks as well.
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Old 23rd January 2012, 11:51 AM   #3
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I would have expected to see this post on the Dynaco forum
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Old 23rd January 2012, 12:20 PM   #4
ElCid79 is offline ElCid79  United States
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Whats that forums adress.
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Old 23rd January 2012, 03:31 PM   #5
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The Stereo 70 was a decent amp, though not exceptional, but IMO the cost to operate one today is more than I'm willing to put up with, as with most tube equipment. Good tubes are expensive and the output tubes need to be replaced every now and then. There are all manner of mods available to improve it- that should tell you something right there.

The Stereo 120 is widely considered to be one of the worst solid state amps ever produced, both sound-wise and for reliability. One should probably have one for that reason alone.

New kits will likely have improvements and I can't comment on those, having no experience with them.

Don't get me wrong as I've owned a lot of Dynaco equipment and enjoyed most of it. It's just that we've come a long ways since then and can do much better, especially DIY.
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Old 23rd January 2012, 04:30 PM   #6
akimmet is offline akimmet  United States
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The st-120 on Tubes4hifi.com has an unfortunate name, the version on his site is a st-70 heavily modified to run kt-88 output tubes. His kits have upgraded power transformers and much better driver circuits. That eliminates 2 of the st-70's major problems. The only issue left is the chassis size/layout.
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Old 23rd January 2012, 05:45 PM   #7
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I have looked at the ST-70 and the ST-120 on that website and they look nice. I have read that the ST-70 and it has been called the poorman's McIntosh and with 350,000 made, it says something about the amp itself. With regards to the new ST-70 amps being made, a lot of the problems that were known with the older original Dynacos have been addressed. I have emailed Bob Latino and for his kits it seems that they are straightforward and easily done by even a novice such as myself. There probably are worse and better PP amplifiers out there, but at this price and to have everything minus the solder, soldering iron, and time it is hard to beat.

If you want for a broader opinion to what it has been compared to, then look at a website that has been in a few posts on diyaudio.com

The Ten Most Significant Amplifiers of All Time | AVguide

And at 9 pages, it makes for an interesting read to as what staffers there think is the best of all time. Probably all subjective, however it gave me something to think about.

If it is DIY kits that you are looking at, take a look at oddwatt offerings from oddwattaudio.com or the Elekit 6550 SE amp from vkmusic.com

(I'm probably going with a ST-70 a lot later on after i am done my first three projects, so there might be some bias)
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Old 23rd January 2012, 06:13 PM   #8
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The main positive quality of the *original* ST-70 and the lower power SCA-35 were the output transformers. Being smaller and lower in power, due to certain realities of winding output iron they happen to have a good bandwidth.

ALL of these early tube amp designs used a fair amount of global loop feedback - mostly to maintain the specification that was more or less *required* in that day of "20cycles to 20,000cycles +/- 1dB". Remove the feedback and most of the output iron would not permit a flat response to 20kHz. The effect of this is/was to make squarewaves, especially if there is any reactance to the load (and there is...) have a fair amount of ringing. The more feedback and the less the bandwidth of the output iron, the more ringing is introduced.

The input stage of the original ST-70 did some things with the input stage to in effect add some "EQ" so that the effect of the feedback would be less severe...

So my point is that modern variants of these amps, using different input stages could well sound better, a lot depends on things that one can't really know without seeing specs, schematics and actual real world tests of the amp.

It's impossible to know what these different companies have done or engineered for these new output transformers. It is certainly possible to improve on the old Dyna iron, but then it's not Dyna iron! Copying Dyna iron depends on proper reverse engineering of the old one, and then proper reproduction...

Anyhow, kits are nice, fun and can always be modified by the owner at a later time and date! And, you will know what is inside.



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Old 23rd January 2012, 06:59 PM   #9
ElCid79 is offline ElCid79  United States
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Fwiw I was looking at the VTA kits from tubes4hifi. Not an original. I like having the higher power output than they smaller ones. But if it as the expense of significant interference and distortion it is not worth it. Does anyone know offhand of any thuroigh reviews of the various kits. I have been searching and they are tough to come by.
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Old 23rd January 2012, 07:00 PM   #10
ElCid79 is offline ElCid79  United States
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Sorry for the typos. My cellphone has been acting up.
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