My modern version of a Dynaco ST70

[Wardsweb]

This is what I came up with for building a modern version of a Dynaco ST-70. The only original parts used were the output transformers. Everything else is new. I upgraded parts and driver board. I drilled and punched a chassis for the new layout and had it chromed. I build a new cabinet out of Baltic birch and veneered it in cocobolo. I was inspired after the Quickie I built with a similar cabinet design.

 

[Paul Joppa]

Sweet!

 

[Paul Birkeland]

Can you build me one?

That is really pretty, whose driver board did you decide on?

 

[Grainger49]

WOW !

That is incredible.  What are the two red topped things between the output tubes and the driver tubes?

 

[Wardsweb]

Can you build me one?

That is really pretty, whose driver board did you decide on?

I used Shannon Park's board. You can see in depth details on my website:

http://wardsweb.org/audio/ST70/

 

[corndog71]

That is one sexy amp!

 

[ironbut]

Beautiful work!
How hard was it to do the veneer?

 

[Wardsweb]

Beautiful work!
How hard was it to do the veneer?

Not hard at all actually. The side you glue and then trim. The top is one piece. I glued it first and then cut out the center.

 

[Wardsweb]

WOW !

That is incredible.  What are the two red topped things between the output tubes and the driver tubes?

They're several test points on the chassis used for setting bias. The original amp had the tube socket on the front. I opted for a some nicer tip jacks.

 

[Grainger49]

I take it that the right and left pair of output tubes are still biased together?  I got a schematic some time back that allowed bias for each tube and allowed using non matched tubes.

 

[Paul Birkeland]

Let's see the inside!

 

[mrarroyo]

That is sweet indeed! How many watts does it put out? I wonder if I could use it to power my AKG K1000, and if yes how much to build me one?

 

[Grainger49]

The Stereo 70 is 35 WPC.  That was part of Dynaco's numbering scheme.  The parts are mostly being cloned by a number of companies.  Luther bought his "junker" ST-70 for the old, desirable, cloth insulated  wire output transformers.  

If you use the link he supplied in reply #4, you will find a parts list.

And with a few more pictures of the inside goodies and this MANUAL downloaded you can build your own.

(That is a hot key.)

 

[Paul Birkeland]

K1000's are very nicely driven by Paramounts, and the DC on the filaments keeps it super quiet. Oddly enough, 2A3's are plenty of power for the K1000. I will test the Stereomour also to see if it is suitable for K1000 duty, but I'm somewheat skeptical.

 

[mrarroyo]

The Paramount using the 300 tube looks awesome! However, I would not be able to build it due to both poor soldering technique and poor eyesight. Since I would have to have it built I will have to wait until I can come up with $2,000. Thanks.

 

[Cary]

WOW! You still are the master!

 

[baddog1946]

That's a beautiful piece of work. I was so inspired I am making a smaller one for my extended foreplay III. Using cocbolo veneer as well. Is there any wood more beautiful than cocbolo?
You are the master. You have both electronics and woodworking down pat. My hat is off to you.

 

[Wardsweb]

That's a beautiful piece of work. I was so inspired I am making a smaller one for my extended foreplay III. Using cocbolo veneer as well. Is there any wood more beautiful than cocbolo?
You are the master. You have both electronics and woodworking down pat. My hat is off to you.

I thank you sir, but I feel I'm only good at best. Even that has taken years of trial and error...lots of errors. I think what most people key in on is my obsessive behavior. I want things one way - right.

 

[Paul Birkeland]

You know some of us are patiently waiting for inside photos...  I am guessing you are spending a ton of time perfecting this beast?

 

[Wardsweb]

You know some of us are patiently waiting for inside photos...  I am guessing you are spending a ton of time perfecting this beast?

My appologies, the amp was set aside for a few more pressing items that needed my attention. Things like my wife asked nicely for pull out drawers for her pots & pans, my son informed me he wants to take my 1955 Belair to prom and my truck decided to stop running. The drawers are made and sitting in the floor to go in, I did brakes all around with wheel cylinder rebuilds on the 55 and my poor truck still doesn't run. Did I mention, I just completed an ISO recertification audit at work?

I will return to the amp which is still sitting on the table in the sun room, but it may be a few weeks.