Dynaco ST70 Upgrade

I just got a one of the Dynaco ST70  upgrade driver boards from http://www.tubes4hifi.com/ the VTA70 and I was very happy with both the performance and customer services from the folks at Vacuum Tube Audio.

This driver board came with great quality components, as well as great instructions on how to assemble the kit. I had to order a replacement current regulator and they sent one out within one day of getting my payment. They also sent another layout diagram to make sure that I installed the transistor correctly. The service was top notch.

This board replaces the single bias control per channel with individual bias controls for each of the output tubes. (2 per channel) It also replaces the large can filter cap with 4 common electrolytic capacitors  that are more cost effective to replace and easier to source.

So how does it sound? well after about 10 hours of listening all I can say is WOW it is a huge improvement over the old driver board, it sounds way more open and the sound stage is more focused. The amp also sounds much faster to me. I compared it to a Scott LK150 in the past before the upgrade the LK150 (stock) sounded much clearer and more transparent. and since the upgrade this ST70 is on par or exceeds the sound of the Scott. Overall I am in love with the new sound of my ST70.

As tested:

  • Dynaco ST70 with cloth leads on output transformers
  • Winged C Svetlana EL34 Tubes
  • RCA Blackplate NOS 12au7 Driver tubes in VTA70 driver board
  • JJ gz34 Rectifier

the other mods are Gold Input Jacks, Updated binding posts (banana plug) and Dale 1% Resistors and 99.99 Silver wire
VTA70v12-019

 

Dynaco ST-70 For Sale – SOLD

Dynaco ST-70 amp
Here we have an extra clean original Dynaco ST-70 Tube Amp, with cloth transformer leads,NOS dynaco branded 7199 Driver Tubes. a NEW Sovtec 5ar4 and a matched quad of Electro Harmonix el-34’sOverall Electronic Condition :
Amp has had 2 caps changed on the driver board; and were replaced with matched orange drops.on the underside of the amp you can see there is some slight discoloration on the bottom of the driver board from the heat generated from the 7199 tubes,
Also you will see a small amount of wax that has leaked out of the choke transformer, it has no effect on the discoloration.

Build Quality:

  • Since this is a Kit, the build quality is top notch, all heater wiring was routed in the correct way and twisted to ensure quiet operation; the layout was done correctly and the soldering looks very professional.

Appearance:

  • The lettering is all intact, and the chassis plating is in VERY good condition with slight pitting by the center power transformer.
  • The bottom as a few scratches and as you can see from the photos the rubber feet are missing.
  • The Tube Cage is clean; however there are a few scratches on the top surface, as well as a few minor paint chips.

Tubes:

  • The NOS 7199 tubes test Very Good / Strong + on my B&K tester(100 is new and these test 98+)
  • EL 34 tubes have about 20 hours on them and were purchased as a matched quad, they hold bias well.
  • 5AR4 tube has also about 20 hours and tests strong / new

Sound:

  • This is my second ST-70 and by far the better sounding, it also is the most original, I have played it using a Dynaco PAS2/3 preamp with an audio lab dac and the sound is fantastic, transparent and clean, it can compete with my vintage Scott in clarity and warmth. overall this is a great example of vintage American Tube Technology from the Golden Era of HiFi.
  • Click here to see the review from Audiomagazine –
  • Click here to see the review from Stereo Review both from 1959!

front pannel Dynaco ST-70

front pannel Dynaco ST-70 Top View of this ST70 in Showing the conditionBottom - Stereo 70 From Dynaco- very clean and good build quality

Bottom - Stereo 70 From Dynaco very clean and good build quality

Bottom - Stereo 70 From Dynaco- very clean and good build quality

ST 70 Driver board with original dynaco 7199 Tubes

ST 70 Driver board with original dynaco 7199 Tubes

Top View of this ST70 in Showing the condition

Top View of this ST70 in Showing the condition