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

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tube & parts sales, contact ned@triodeel.com
new & used audio equipment sales contact jim@triodeel.com
Triode Electronics, 2225 W Roscoe St, Chicago, IL 60618
Phone number 773-871-7459 FAX (on 24 hrs) 773-871-7938
Open 12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun

Our Dynaco (TM) ST-70 Conversion Board (includes instruction manual)
See the schematic by clicking here For more details, click here
Blank board, $59.95, Board w/parts, $74.95, stuffed board, $99.95
Upgrade to Sprague coupling capacitors on above, add $12
Manual for ST70 board (if you decide to get a board later the price can be applied to the cost of the board) $9.95
Boards require 2 EF86 tubes (EF86 are $12.95 each from us) and one 12AU7 or 12BH7 or tube (see tube page for numerous types avail.). We suggest ECC99 or 12BH7 for best results.
View of ST70 board installed (courtesy Tom McNally)

SDS Labs 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! Increases capacity from the original 30-20-20-20 to 50-180-50-50 uF at 500V, and also replaces the bias supply capacitors & diode as well.
Blank board with instructions & mounting hardware $19.95 (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 & hardware $49.95

Our Mark 3/Mark 2 Upgrade Board, (includes instruction manual..)
See the schematic ,click here More details , click here
Pair of blank boards,. $69.95. Pair of boards with parts for completion, $84.95.
Pair of stuffed boards, $119.95.
Upgrade to Sprague coupling capacitors on above, add $8
Manual for Mk2/Mk3 board (if you decide to get a board later the price can be applied to the cost of the board) $9.95
Boards require 2 12AU7 or 1 12AU7 + 12BH7 or ECC99 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.
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 $19.95 (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 $49.95

Our Mark 4 Upgrade Board, (includes instruction manual..) The same successful & renowned (cascode-triode input and long-tail inverter) circuit as ouir Mk2/Mk2 board, downsized to fit a Mk4.Available March 2001
Schematic other than pad numbers, same as Mk3 board, click here More details , click here
Pair of blank boards,. $74.95. Pair of boards with parts for completion, $89.95.
Pair of stuffed boards, $124.95.
Upgrade to Sprague coupling capacitors on above, add $8
Manual for Mk4 board (if you decide to get a board later the price can be applied to the cost of the board) $9.95
Boards require 2 12AU7 or 1 12AU7 + 12BH7 or ECC99 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 and Mial low-loss polystyrene capacitors, and gold-plated 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.$6.95 (per amplifier)
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.$1.95
Bias Repair Kit: Capacitors, diode & terminal for repairing bias supply. Not required on ST70 when SDS Labs capaciotr board is used.
For either ST-70,Mark 4, Mark 3 or Mark 2.One required per amp. $2.95
Replacement choke for Dynaco C-354, fits ST70, Mk2, Mk3, Mk4. $15.95

Replacement input jacks, output binding posts and other useful items for your Dynaco can be found on our 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 EF86 (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 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 an Alternative Power Supply Strategy guide to deal with the occasional pesky Mk3/2 power supply problems, and a special section on Mark 2's.
The ST-70 board uses an EF86 front-end , which is the lowset noise & distortion audio pentode in current production..don't be scared of this pentode, like Sam I Am, you'll be pleasantly surprised. It's a measurable improvement over 7199 and 6GH8.
Both boards use a split load phase inverter, which requires no adjustment or "selected tubes" for proper operation. Both boards have similar gain to the the original, so don't require additional tweaking for proper operation.

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[Tube Data Page ][Tube & Tube Amp Links Page ][Dynaco Upgrades] [Dusty Files Part 1 Part 2 ][Mailbag Page][Schematic Index][Studio Schematics][Altec Page][Area 51][Frequently Asked Questions][How To Find Us]

 

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