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Dynaco ST-70, What an Amazing Amp!!

zastin17

zastin17

Active Member
So I got myself an early Christmas present. And I am very happy I did!! What an incredible midrange, and beautifull highs. So diffrent from anything I've heared, but is so fun to listen too.

Sooo holographic, so mutch coherent texture. The sound has a physical presence that is very, very real. Very hard to describe, but nothing like any SS amp I have ever owned.

Even the very early SS Sansuis which are said to sound "tubie" but I dissagree in comparison. Deffinitly still sounds like a SS amp to me.

Every single album I play sounds like a different recording. Hearing many things I didn't hear like I did on SS amplifiers in different ways. What an amazing experience!!

Very involving, and extremely "tactile" is how ide describe it. And soo mutch more power than I was expecting to receive from this awesome amp!

The only other tube amp I've ever played with was an old Bell 404, 14w PP, cartidge deck/amplifier. That gave some of that tube sound, but only had enough power to drive very small, and/or very efficient speakers with only an 8ohm tap.

While this ST70 is driving everything I own without issue!!! Magnepans, ESS AMTs, you name it!

I bypassed the large multicap, and am still using the 30uf sections while I wait for an entire replacement!

Also I replaced the Diode, and the 50uf bias caps with 100Uf, 200v.

This thing sounds amazingly beautiful!! Driving my Apogee Graz KLM5 Ribbons, and Upgraded Ohm Walsh 2XOs no problem!!
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Very nice shape
I still have my first one 40+ years ago
Fellow I got it from here in NYC
He said my life would never be the same with your going to all Tubes
So right. Enjoy your amp best bang for the buck
Sweet Mids and nice presentation for sure
 
Erhard-Audio said:
that is a very clean example. It was either looked after and stored extremely well or it was one of the last ones built! A great find!
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I believe it may be an older one, as the transformer leads are cloth covered. But I may be wrong.

Is there anyway to check dates? I can't find any in the unit.

Luckily, it seems the chrome finish was covered in a farily thick waxy substance, which I assume is tobacco tar, but it seems protected it from rust.

A few hours of Netflix, Polish, and a box of Qu tips later, it came out looking brand new. Even better looking after these photos where taken.

It also seems it saw very little use from the lack of burn on the board.
 
There should be a two digit date stamp on the underside of the power transformer. Mine is stamped 59, indicating the it was made in 1959. As I understand it, the PT was made then and purchased by Dynaco but may have been used for a period of years, until that run was depleted. The bias pots should have a month and year. I replaced and threw mine out before learning this.

The plating is actually nickel which tarnishes to a whitish color, I believe.
 
Blackdog61 said:
There should be a two digit date stamp on the underside of the power transformer. Mine is stamped 59, indicating the it was made in 1959. As I understand it, the PT was made then and purchased by Dynaco but may have been used for a period of years, until that run was depleted. The bias pots should have a month and year. I replaced and threw mine out before learning this.

The plating is actually nickel which tarnishes to a whitish color, I believe.
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Nickel, yes. It has a "softer" sheen than chrome and seems less susceptible to pinhole rust pitting. It is a softer surface finish than chrome.
 
Thought I would just add to this post. Its been a while and I love this amplifier!!

This Dynaco will be preserved to Factory as close as possible.

I have learned a ton about tubes and tube circuits and have been building my own Tube Amplifiers. I don't think I need to buy another Tube amp ever again, I can just build it!! HAHA

Anyway. I redrew the Hafler 1959 Schematic, i'ts very clear to read compared to the old one, and may help people in the future, so I'm just dropping that here: https://i.imgur.com/ZsWQjX7.png
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Nice. While I love tube guitar amps, tube hi-fi hasn't interested me much. The Dynaco ST-70 has always been the exception. I'd love to get one of the modern reincarnations of this amp.

Yours is sweet. Enjoy.
 
I've got a vintage Dynakit ST-70 that I trash picked from a neighbor. It's down in the queue but I'll eventually get to it. It looks rough compared to this one. Good to hear someone is enjoying theirs.
 
Nice find. I currently use an AVA Ultravalve which is a further developed ST 70 circuit utilizing 6GH8 tubes instead of the 7199. It is a very dependable and nice playing amp.
 
Time to start saving up for spare 7199s if you need them. Suckers ain't cheap ... especially house branded.
 
Many of the amps based on the Dyna 70 OPTs and chassis, like the Latino VTA, are fundamentally different designs rather than variants of the original. Dynakit parts supplies new original Dyna amps.
 
Pio1980 said:
Many of the amps based on the Dyna 70 OPTs and chassis, like the Latino VTA, are fundamentally different designs rather than variants of the original. Dynakit parts supplies new original Dyna amps.
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The Dynakit site says "Out of Stock" on everything. This might be due to Magnetic Components closing. I believe they were the source of the transformers.

Jack
 
No, they have a new supplier from what I was told. I bought and built a ST-35 from Dynakit after Magnetic Componants closed. Dynakit was out of stock for awhile, but back up and running again when I bought the kit from them.
If you messaged them I'm sure they would be able to tell what the problem is this time.
 
one thing that has always driven me nuts about Dynaco schematics is the lack of voltages. Even just voltages at the power supply nodes would be helpful, rather than having to dig through the assembly manual to find it. Maybe something to consider adding to this if you're up for usability enhancements.
 
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