I am new to this forum and want to share my efforts in rebuilding a ST70 amplifier.
I bought a stock ST70 (1961) on EBay that looked like this:
I completely stripped the amp and cleaned the chassis:
I did not change the original topology of the amp except for the power supply.
The power transformer was replaced by a Triode Electronic transformer.
I needed a 230V version anyway, so I decided to buy a beefier transformer instead.
Modified the multicap for the 80-40-30-20 version of Dynakit and replaced
the selenium cell for an ultrafast rectifier diode type BYV29.
All other components are new except for the chassis, the A470’s,
the choke, the speaker connectors, the bias pots and the cathode resistors.
I used Belton tube sockets (except for the sockets up front that are still the
original Amphenol sockets), resistors are Beyschlag (red brown ones),
Takman and Kiwame (green). All carbon types. For coupling I used Auricap capacitors.
Tubes used: a matched quad JJ EL34L, Silvania and/or RCA 7199, Philips nos GZ43.
The mono-stereo switch was left unused.
Most rebuilds are done using PCB’s for the front end of the amp.
I disliked the PCB on top, so I decided to follow another approach.
You hardly ever see a hard wired ST70, so I fully hard wired the frontend using
stand offs, terminal strips and a sub chassis that is covered with a laser-cut
chrome steel plate on top. First attempt sub chassis:
This one worked fine but I was not completely satisfied.
I used this one for another ST70 that I rebuild for my brother.
I thought it over and designed a less chaotic topology.
Layout of the final version of the front-end:
Dimensions (in millimeters) of the sub chassis:
Dimensions (in millimeters) of the cover:
Top view of the completed ST70:
This is how it looks underneath:
Some detail shots:
Comments and critics are welcome.
Those of you who might be interested in (re)building the ST70 this way,
may benefit from this layout. Mail me and I will send you the drawings
in PDF format, or if so desired, in Autocad DWG format.
All drawings are in a 1 to 1 scale.
See also my triode - ultra lineair mod., Post n°35:
Here are the two finished ST70’s and my ‘Classic One’ preamp:
The Classic One is the incredible sweet sounding design of
Triode Dick consisting of a SRPP stage (6N30) and
a cathode follower stage (6N6) and here it is:
If you want to know more about this beauty, mail me.
All ST70 photos (click on the photo displayed in the
center for a larger view) can be found here:
At this time I (temporarily) replaced my ST70 for the Allen Wright's PP-2C power amps (monoblocks)
Text on this forum is all in Dutch, but there are a lot of photos and schematics, if you’re interested. Use Google Translate.
Last edited by rovano on Sun Mar 24, 2019 7:48 pm; edited 6 times in total (Reason for editing : Addition of links)