Dynaco Stuff : Upgrade PC Boards for Mk2, Mk3, Mk4, ST70
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
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
What's so special about our Dynaco
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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Dynaco Stuff : Upgrade PC Boards for Mk2, Mk3, ST70