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Review and Measurements of Dynaco ST 70
- Thread starter amirm
- Start date
Not sure what's out there these days (I designed my own), but Joe Curcio's board was pretty good and I bet there's some version of it still floating around. His used ECC88-types, and I've done some adaptions of it to use 12AT7 as well, since JJ is making some really excellent ECC81/12AT7 at a very good price.
If someone wants to design a PCB, I can provide what I think is a very good circuit at no charge (I don't make money from hifi sales, it would be a conflict-of-interest in my opinion).
DKT88
Active Member
That's good news. It was a very well thought out design, and Joe seemed like a good guy when I met him a few years back.
DKT88
Active Member
There is this: https://avahifi.com/collections/tube-power-amplifiers/products/ultravalve-vacuum-tube-amplifier
And this: https://avahifi.com/collections/dyna-and-hafler-rebuilds
I have not spoken with Frank in years and he would not remember anyway but I greatly respected hm (and still do). A no-nonsense kinda' guy in the audiophile world (Roger Sanders is another guy I admire, and he now lives just a couple of hours away, really need to see he and Angela again).
And this: https://avahifi.com/collections/dyna-and-hafler-rebuilds
I have not spoken with Frank in years and he would not remember anyway but I greatly respected hm (and still do). A no-nonsense kinda' guy in the audiophile world (Roger Sanders is another guy I admire, and he now lives just a couple of hours away, really need to see he and Angela again).
Last edited:
Newk Yuler
Active Member
- Joined
- Mar 5, 2019
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Yup. I have one of these, too. Buried somewhere. Are we forming a club?
Stereophile measured the Dynaco Stereo 70 II, not the same, but...
https://www.stereophile.com/content/dynaco-stereo-70-ii-power-amplifier-measurements
https://www.stereophile.com/content/dynaco-stereo-70-ii-power-amplifier-measurements
Jaimo
Active Member
I have a ST35, ST70 and a pair of MK3 clones - these are fantastic legacy products and they sound great. My MK3's are point to point wired and modified with switching B+ Neurochrome regulators. To my ears, they sounded better driving my Magnepan MG1.6's than a Bryston 4BST.
restorer-john
Grand Contributor
Wow. That exchange between Stereophile and Bob Rapoport is just just horrible. Never seen anything like it.
DDF
Addicted to Fun and Learning
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- Dec 31, 2018
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I thought you were alergic to class d (hypex)?Nope, there's more of us than you think...
OP
- Thread Starter
- #33
I was asked for wideband FFT to see if there are any problematic ultrasonic issues. Here it is:
It is pretty clean.
It is pretty clean.
OP
- Thread Starter
- #34
I swapped the tubes from left to right channel and vice versa. It made the good channel a bit worse for distortion and didn't improve the other. However, the levels now completely match which is good.
Adjusting the bias to lower values improves things a bit. It raises 2nd harmonic and lowers the 3rd. I should measure the inline resistors to see what the actual values are.
Stability is pretty poor though. It went into nasty oscillation a few times. Could hear the chassis rattling! What are the typical causes for this?
Adjusting the bias to lower values improves things a bit. It raises 2nd harmonic and lowers the 3rd. I should measure the inline resistors to see what the actual values are.
Stability is pretty poor though. It went into nasty oscillation a few times. Could hear the chassis rattling! What are the typical causes for this?
Low or high frequency? if the latter, likely the same as any other amp- inadequate phase margin, fixed by either by lowering the dominant pole or increasing the compensation cap in one of the feedback networks.
OP
- Thread Starter
- #36
Stunning. Some of these people have no business sense whatsoever:
It only gets worse after this!
OP
That might be the power supply coughing as the amp does some squegging. It's still an HF oscillation, but it sucks power so the supply sags and the power transformer goes in and out of saturation.
Ouch. I just looked at the pictures and thought I was done.
SIY, is there a driver board you'd recommend that ditches the hard to find 7199? I have a pair of clean MKIV's collecting dust for the last 30 years.
I may be the only guy on ASR that owns both amps at opposite extremes of the SINAD graph.
Hi DDF,
I have a pair of monoblock Hypex NC400 and a set of Kebschull 35/70 monoblocks from a Bavarian manufacturer that is of course long out of business (from the early 80s -- the amp based on the EL34 pentode power stage, EF86 pentode voltage amplifier and 6SN7 concertina phase splitter design developed by Harold Leak for the TL/12 "Point 1" and TL/10 in the mid 40s - 50s).
Although I don't know what the Kebschulls rate in SINAD, I can imagine it's something like the ST 70. The design is what was called "ultralinear" back then. If they didn't weigh like a sack a bricks, I should send them to Amir, so that we can we can see what progress ancient, to old, to those new boutique retro tube amps have made.
I guess it's best to cover the ends of the spectrum, as you say.
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