Dynaco Stuff : Upgrade PC Boards for Mk2, Mk3, Mk4, ST70

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Troubleshooting and
Triode Connecting

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Our Dynaco (TM) ST-70 Conversion Board (includes instruction
manual)
See the schematic by clicking here
For more details, click here
Tubes
are not included.
You can also Upgrade to Sprague coupling capacitors on
above
Manual for ST70 board
Boards require 2 EF86 (or
6Au6/EF94 for that version) or compatible tubes and one 12AU7 or 12BH7 or tube
(see tube page for
numerous types avail.). Our newest board also supports 6922 type tubes as
well.
View of ST70 board installed (courtesy Tom McNally)

Triode Electronics ST70 Capacitor
Board:This Power Supply board replaces the original can capacitor in
Dynaco ST70. (You can leave the old one there for looks if you like) Bolt on
standoffs under the output transformer, no cutting or drilling required to
install, just bolt in, hook up the wires and go! NEWLY DESIGNED! Upgrade Cap
Board: New Updated Version!!! This is a new, updated, version of the classic,
SDS Labs, ST-70 Capacitor board. We have upped the capacitance to over 500uF @
500V (Increases capacitance from original 30-20-20-20 to 40-195-135-135) while
at the same time shrinking the board to make it fit into the chassis more
comfortably. The board still replaces all bias supply components and we have
also added 0.1uF Wima MKP series metallized polypropylene bypass capacitors onto
the board. There are no more surface mount resistors as used on the old boards,
instead we have standard axial metal film resistors that are easy to mount and
solder in place. There is also a cutout on the back of the board to make
clearance for using binding posts in the amplifier rather than the original
screw terminal strips. The board is a high quality .062 FR4 2oz Copper with
plated through holes which allow you to solder/resolder connections with the
board already mounted in place. Now with clearer and more detailed
instructions.
(Note that the maximum capacitor size is 25mm
long by 30mm diameter, board requires 8 pieces rated 250V or
more)
Board with instructions, all capacitors, parts & amp;
hardware.

Our Mark 3/Mark 2 Upgrade Board, (includes instruction manual..)

See the schematic ,click here More details , click
here

Each amplifier requires one board. Tubes are not included.
You can also
Upgrade to Sprague coupling capacitors on above.
Manual for Mk2/Mk3
board
Boards require 2 12AU7 or 1 12AU7 + 12BH7 or ECC99 or 6CG7/6FQ7 per
board (double this for two amps). See our tube
page for types available. We suggest using 12AU7 + ECC99, 12BH7 or 6CG7 for
best results.
View
of installed Mk3 board (courtesy Tom
McNally)

SDS Labs Mk3/Mk2 Capacitor Boards:These Power Supply boards
replace the original can capacitors in Dynaco Mk3& Mk2. (You can leave the
old one there for looks if you like) Fit on standoffs under the output
transformers, no cutting or drilling required to install, just bolt in, hook up
the wires and go! The Mk3 board increases capacity to 50-50-50-50 uF (two 100 uF
in series per section) and the voltage rating to 630V per section (800V if you
leave out the .1 uf bypass caps) eliminates capacitor problems the original
525V rated cap had that are caused by high line voltages and allows the use of
solid-state diode replacements as well as the original tube (5AR4/GZ34 or 5U4)
rectifier.The Mark 3 board also works on Dynaco Mark 2 (50 ohm 5W resistor
required for Mark 2, not included), and most Sunn amplifiers that use Dynaco
transformers (some Sunns will need additional resistors not included in the
kit).One kit required per amplifier.
Blank board with instructions
& mounting hardware (Note that the maximum capacitor size is 25mm
long by 25mm diameter, board requires 8 pieces rated 300V or
more)
Board with instructions, all capacitors, parts &
hardware

Our Mark 4 Upgrade Board, (includes instruction manual..) The same
successful & renowned (cascode-triode input and long-tail inverter) circuit
as our Mk2/Mk2 board, downsized to fit a Mk4.
Schematic other than
pad numbers, same as Mk3 board, click here
More details , click here

Boards require 2 12AU7 or 1 12AU7 + 12BH7 or ECC99 or 6CG7 per board (double
this for two amps). See our tube page for types
available. We suggest using 12AU7 + ECC99 or 12BH7 for best results.
For
single pieces instead of pairs, deduct 40% off above prices.

Parts supplied with above boards include low-noise metal film
resistors, Xicon polypropylene capacitors, and ceramic tube
sockets.

Mark3/Mark2/Mark4 Dual Bias Kit: Allows separate adjustment of bias
for each output tube when used with our board. Includes bias-supply caps &
diode. Requires drilling to install.Works with our board ONLY.

Bias Controls for Dynaco. Available in standard 10K, or 25K (allows
wider range to allow for use of tubes other than stock). Fits all Mk3, Mk2, Mk4,
ST70.
Bias Repair Kit: Capacitors, diode & terminal for
repairing bias supply.
For either ST-70,Mark 4, Mark 3 or Mark 2.One
required per amp.
We also offer a Replacement choke for
Dynaco C-354, fits ST70, Mk2, Mk3, Mk4.

Replacement input jacks, output binding posts
and other useful items for your Dynaco can be found on our
Dynaco Parts Page

Replacement Tubes for your Dynaco may be found on our
Tube
Page

What's so special about our Dynaco upgrade
boards?
The object of our upgrade boards is to provide a dropin
replacement for the original boards that would result in a perceptible
improvement in sound quality and overall performance, use readily available
tubes, and, in keeping with the original Dynaco philosophy, sell for a
reasonable price. In other words, using our board, you get improved performance
just by installing the board, there aren't any additional controls to bother
with, or shoehorning in more parts in the amp.

There's certainly other "dropin" boards, but most of them use 6GH8 or a
similar triode/pentode which are a step back in performance compared to the
original 7199, and no better than a 6AN8. Basically, you're getting improved
quality parts, but no better performance otherwise than the original board if it
had better parts to begin with...actually, on the average, 6GH8 have worse noise
performance than 7199's do. Our board with either 6AU6/EF94 (ST70) or a cascoded
12AU7 (Mk3/Mk2 board), gives improved performance in this respect, and most
people agree it sounds better, too. The ST-70 board also cuts DC grid circuit
resistance of the EL34's by about 2/3rds, which reduces or eliminates pesky
bias-drift problems.

Our board's a great choice if you really want to learn more about how your
amplifier operates, too. You see,unlike many other  modifications, you are
not totally locked in to only certain components, nor are you stuck with
unchangeable circuit values which limit the versatility of your amplifier and
further modifications. There's no "big secrets",you don't need permission from a
"guru" to change or tweak it, the 20 page manual has instructions for about
every change you could imagine making. Instructions are included for triode
connecting the output tubes, which will give you a taste of hi-end triode-itis
for the cost of 4 resistors, about $1.
So, you've got a choice..you can just
plug in & play, or you can do your own experimenting if you'd like to, learn
a lot and become your own neighborhood Dynaco guru. And you won't break the bank
doing it, either.
The stock board parts kit includes metal film resistors,
polypropylene & polystyrene capacitors, and gold plated tube sockets. which
do just fine..but if you like you can modify many component values and try
different or exotic parts and tweak to your heart's content. The boards will
adapt to output tubes which need very low drive circuit impedance/ DC grid
resistance like 8417's- or may be modified to whip out enough voltage to drive
6B4's!! (even 300B's might work..we haven't tried it yet..).
The board
sounds fine even with the off the shelf, current production tubes, and special
grading and matching is not absolutely necessary. It is a good example of what
can be done with the original type of circuit with improved components, and
makes a good case for the virtues of simplicity and short signal path in audio
design. PC1 boards emulate the simple but highly effective (due to the short
signal path and single gain stage) original Dynaco circuit, but with lower hum,
noise, distortion and a wider voltage swing across heavier loads than a
7199,6GH8,6BL8/ECF80, 6U8/ECF82 or 6AN8 are capable of.
The manual includes
information on adapting the amplifier to different output & board tubes,
adjusting resistor & capacitor values if desired, plus a comprehensive
Troubleshooting Guide.
The Mark 4/3/2 board uses a cascoded triode
front-end, which gives "pentode gain with triode noise" and allows the use
of a wide variety of possible tubes with pinouts same as 12AU7, by simply
changing 2 resistors on the board.
The Mark 3/2 manual also includes a
special section on Mark 2's.
The 6AU6 ST-70 board uses an 6AU6/EF94 (or
compatible tube) front-end..don't be scared of this pentode, like Sam I Am,
you'll be pleasantly surprised.There's a plethora (at least a dozen types)
of tubes that are cheap and pin-compatible with
6AU6 if you want to try some bargain tube rolling! We are as always offering our
Newest Upgrade Classic EF86 version as well. This one has won many shootouts and
many hundreds are in happy service right now. Our newest version of the EF86
board has been slightly revised to accept 6922, 6DJ8, 7308, and 6CG7 in the
phase inverter position as well as 12AU7, 12BH7, and ECC99 that were previously
supported.

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Upgrades Page
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Data Page ][Tube& Tube Amp
Links Page ][Dynaco
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Schematics][Altec Page][Area 51][Frequently
Asked Questions][How To Find
Us]

Dynaco Stuff : Upgrade PC Boards for Mk2, Mk3, ST70

Transformers

Troubleshooting and
Triode Connecting