Review and Measurements of Dynaco ST 70

[Jaimo]

I just built up a Bob Latino ST-70. I live in Seattle and wouldn't have to worry about shipping if Amirm would be interested in testing it. New here so not sure how that works.

@amirm - if you are up to testing a variation of the ST70, Westy is your man...The much lauded Bob Latino version introduces a modified driver circuit that supposedly improves the original ST70 performance.

I got it! Let the solder flow...But not too much!

I can’t think of a better way to spend a cold winters night...

 

[AndreaT]

That's a fabulous FR (the good channel) for a 60+ year old tube amp into 4 ohms IMO. Must be some really good OPT TXFs.

A bit of work on the filtering, regulation and tightening up the tolerances to bring the channel balance back into line and it'd be a fun project.

I have a Dynakit ST-35 with the original transformers. It has been in use (heavy use from 1967 until 1983, as it was the only power amp in the family home) for the past 54 years, with updated (x2) boards and tubes. Remarkable.

 

[RoyB]

Finished it. Love the sound with Magnapan MMGs or Klipsch RP

 

[SIY]

Finished it. Love the sound with Magnapan MMGs or Klipsch RP

That's a very pretty build! The meters are a delightful touch.

 

[RoyB]

Meters are DC 0-1v for bias adjustment. Replaced a Yamaha M45. This amp sounds do much better. Much more "mellow" without the strident highs the SS amp had in my listening room. Using a Schiit Saga preamp and Bluesound Node2i for source. Could not be more pleassed with my current system.

 

[Sal1950]

Finished it. Love the sound with Magnapan MMGs or Klipsch RP

Wow, what a great looking build, a major thumbs up.
What is the knob for, an input level control or something else?

 

[RoyB]

Yes, input level control. Thanks for the kind words.

 

[jxdking]

I wonder how it compares to McIntosh MC275. I searched through the forum and didn’t find anything regarding McIntosh Tube amp.

 

[Sal1950]

I wonder how it compares to McIntosh MC275. I searched through the forum and didn’t find anything regarding McIntosh Tube amp.

Objective measurements or subjective listening impressions?

 

[jxdking]

Objective measurements or subjective listening impressions?

McIntosh lists 0.25% 1K THD for the latest MC275. I also saw ElPaso measured 0.2% THD with one of old version in his YouTube video, which is a little shy of 60db. Also from the MC275 specs page, the s/n ratio is listed as 105db. This is a quite achievement for a tube amp.

 

[SIY]

McIntosh lists 0.25% 1K THD for the latest MC275. I also saw ElPaso measured 0.2% THD with one of old version in his YouTube video, which is a little shy of 60db. Also from the MC275 specs page, the s/n ratio is listed as 105db. This is a quite achievement for a tube amp.

The Macs had a clever and unique circuit which made them less load dependent and lower distortion because of the reduction in leakage inductance effects. Great overload recovery as well.

Edit: wrong link fixed.

Excellent article about it here.

 

[johny_2000]

I wonder how it compares to McIntosh MC275. I searched through the forum and didn’t find anything regarding McIntosh Tube amp.

I was wondering the same thing.

Probably too expensive for someone to throw away that kind of money for the benefit of audio science.

Even just shipping such heavy units back and forth to someone with measuring equipment would cost a pretty penny.

I'm sure there are many owners of McIntosh tube amps, but they are not interested in any measurements, and are not members of this site.

 

[SIY]

Even just shipping such heavy units back and forth to someone with measuring equipment would cost a pretty penny.

When I'm done my restoration of some MI-75s, I'll show the measurements.

 

[30 Ounce]

Stereophile measured the MC275 here:

McIntosh MC275 power amplifier Measurements

Sidebar 3: Measurements

www.stereophile.com

 

[mlsstl]

I went through a phase about 15 to 20 years ago where I rebuilt a bunch of Dynaco gear. You could still buy used originals fairly cheaply at that point (especially if not working) and I enjoyed the benchwork. Here is my favorite ST-70 -- I disassembled it down to the chrome steel case and polished that then painted the transformer casings before starting the rebuild. process. The driver board was replaced with one from Triode Electronics, power cap was replaced and I used 6L6GCs as output tubes. Sound was a bit gutsier than the more refined EL34s but it was a fun amp. This is the I most regret selling because it turned out pretty good looking and I just like tubes. However, from a practical standpoint, I don't have a good place to use it in any of my current systems, and the new stuff I have sounds better. Life moves on....

 

[Sal1950]

I went through a phase about 15 to 20 years ago where I rebuilt a bunch of Dynaco gear. You could still buy used originals fairly cheaply at that point (especially if not working) and I enjoyed the benchwork. Here is my favorite ST-70 -- I disassembled it down to the chrome steel case and polished that then painted the transformer casings before starting the rebuild. process. The driver board was replaced with one from Triode Electronics, power cap was replaced and I used 6L6GCs as output tubes. Sound was a bit gutsier than the more refined EL34s but it was a fun amp. This is the I most regret selling because it turned out pretty good looking and I just like tubes. However, from a practical standpoint, I don't have a good place to use it in any of my current systems, and the new stuff I have sounds better. Life moves on....

Sweet, I had kept an all original ST70 around for many years (just because). LOL
The only thing not orginal were the bottom panel and of course the tubes, it ran great.
When you have the room to keep them around, the ole school toys are fun to own and play with.