Point to Point SET amp in a Dynaco ST-70 chassis


Well-Known Member
Feb 14, 2008
I had a ST-70 chassis and a bunch of other parts
lying around.
Since I already made a PP amp, I wanted to try a SET.
I considered a few choices, and finally decided to try the
diytube Get*Set*Go in a point to point mode.
This design is clean, simple and
sounds great. It really lives up to it's name.

I used Bakelite sheet (available in electrical shops) as
a back plane.
The config - Transcendar 3K OPTs, Sovtek 6B4Gs, NOS
RCA 6AX5GT and a NOS Raytheon 6SL7. The PT is an
Antek AN-1T300. All parts are thanks to friends and
family in US.

The large coupling caps made by El-Ci-Ar were
given to me by Rajiv.
I made an extension shaft for the pushbutton type
power switch mounted at the rear.
The transformer leads are not trimmed yet, so there are some long, coiled wires in the pic.

I wanted a removable power cord, so used one of
those 3 pin metal connectors (found on temp controlled
soldering irons etc) - had to drill out the hole a little bit
to fit this.


Looks perfect. Dont change a thing. However, you can consider replacing the Bakelite board with an AL or Cu board sometime in future. Can help better dissipate the heat from the 6SL7 on hotter days. A bakelite sheet is not a good conductor of heat.

Seem you are implementing a hybrid tube rectification here. Good thing if yes.
Seem you are implementing a hybrid tube rectification here.

B+ is rectified by the 6AX5GT. No sand there.
The schottky diode full wave circuit seen on the
tag boards on either side are for the DC heaters.

About bakelite, I considered using
a glass-epoxy substrate, but was unable to make time
to go hunt for a largish piece. The area near the
6SL7 does not get too hot as I put in the middle
with lots of space around.

Build log here if you are interested -


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your amp look lovely prasad! :licklips: do post a detailed review of the sound too and a comparison with the push pull amps you've built.

Ok. I missed that. I automatically assumed AC on a low mu triode.

Be in look out of 6A3 which should be available in some forsaken place. Most GE and other US made radio sets had 6A3 in their output stage.

The 6SL7 in its normal biasing will get pretty hot in warm days. Besides, why build up and retain heat in if it can be dissipated easily. Are you running them in SRPP?

Of course all small nitpicks. Great build and I am sure great performance too! :clapping:

your amp look lovely prasad!

Yes. I second that. It looks stunning ! Very classic and 60's look.
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Prasad one more feather to your DIY cap:clapping: ! neat looking one man !

Please do post your impression on sound mated to your single driver speakers,also how is it in comparison with the LM you did sometime back !

Thanks folks! :)

This amp turned out to be better looking than I anticipated.
The ST-70 chassis is pretty nice - very flexible as it
has a variety of holes for various stuff.
I did not have to make a single mod to the chassis,
except to make the power cord hole bigger to fit the
round connector.
Luckily, the Transcendar OPTs fit quite nicely into the
original OPT holes, after a little bit of filing the end cap
holes so they line up.

About the listening impressions, I have just got to
use it for a couple of hours. It sounds very detailed,
especially at lower volumes. The OPTs look
small, but the bass is excellent. Definitely great VFM.
The Sachiko speakers work very well with
this kind of amp, as they are very efficient and present
an easy load.

I prefer this amp to the LM3886 for the Sachikos,
but I think the LM3886 amp works very well for the
smaller, less efficient Recession Buster speakers.

Comparison with the PP KT-77 - I am yet to make
up my mind. I have listened to the PP amp much longer,
and this SET is yet to break in.

Are you running them in SRPP?

No, each half of the 6SL7 drives one channel.
It is a very simple circuit, actually. In fact, I spent more
time building the DC heater circuits than the actual amp.

Hi Prasad,

The amp looks great. Innovative use of the ST70 chassis.

How do the EL-CI AR's sound in comparison to the Orange Drops?

With just a few hours on it, I am very happy with
the performance of this amp. Those El-Ci-Ars are staying
in there! Thanks, Rajiv!
I don't see a need to try out the orange drops.


Prasad,sorry to hijack this thread but I would like to let other DIYers know about these caps.

I have used these oil impregnated film and foil caps( mixed dielectric and polypropylene) and found them to be better than the Solen,Orange Drops and the Infinity TRT caps.They are also inexpensive in comparision to imported caps.

Polypropylene Capacitors,Polyester Capacitors,Polypropylene AC Capacitors,Axial Polyester Capacitors

Thats a very encouraging piece of information.

I use them when prototyping a project. Once the design was stable I would put in a so called better cap. I must give an extended listening with these caps.

You are the second person giving this comment. Another DIY friend who only uses El Ci Ar is his tube amps swears by them. But I never took him seriously as his audio tastes are vastly different than mine.

The fact they are cheap as peanuts helps with my cheapster philosophy !
No, each half of the 6SL7 drives one channel.
Please dont take me otherwise but that seem like weak point. I would have preferred at least a parallel drive when using a tube like 6SL7. The present arrangement is adequate but not the best.

See if you can use an additional 6SL7 or even better 6SN7. You may need to use another bakelite board. Or you can put a CCS load if only using one tube for both channels.

These are small nitpicking. Hope this unsolicited opinion is taken in right spirit.
DIY is that endless quest of constant tinkering for actual and imaginary improvements ; )

BTW I marvel you braveness in putting a pair of Sachiko in what looks like your bedroom. It seems you have managed to manage the WAF most brilliantly. I admire and salute you skills !
managed to manage the WAF

:) Yes, the stars were positioned right and the lady of
the house felt that the Sachikos could be tolerated in
the mid-size spare bedroom. I have taken over an old
dresser and using it as a makeshift audio rack :)
I certainly do have WAF probs with my accumulated "junk".

The Sachikos would do better in a larger room than I have.

The opinion/critical review/sugggestions are definitely
taken in the right spirit, else would not be posting here,
so it's not unsolicited either.
I am grateful for the time folks take to look at
other people's work and encourage them to improve.

For the first SET (and only my 2nd tube effort), the
fool-proof, easy design (and cost!) of the GSG was appealing. This was easy to do in Point-to-point wiring.

Tweaks like CCS, SRPP etc are things to play with on this
foundation, as I understand the concepts better.
I have to brush up my electronics and read
Morgan Jones and other stuff - miles to go.
At this time, I am just the average diy tinkerer
than a designer like some of you folks here.

6SN7 - someone on diytube asked and they said it would
not work well in this design. I have one somewhere, so
I can give it a try one of these days.
BTW, are the IXYS CCS chips available here?

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