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DYNACO-ST70 POWER AMPLIFIER - DRIVER AMPLIFIER & QUAD CAPACITOR UPGRADE
MODULES |
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Many of you have requested that we develop modules to
upgrade the
existing Dynaco design (as opposed to our complete modification package).
You also requested a simple and reliable power supply module. We thank you
for your suggestion and in response
we are very pleased to announce two new modules for the ST-70: our PWB-3U
driver stage (replaces the 7199 board) upgrade module and our PWB-S7U
"Quad" capacitor replacement module.
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CAE PWB-3U DRIVER STAGE
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PWB-3U
Driver Amplifier |
Schematic
Diagram |
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- All Triode Full Direct Coupled Circuit Design Provides Ultra High Stability and Highest
Sonic Purity
- Accepts 6922, 6N1P, 7308, 6DJ8, or 6CG7
- Instrumentation Style "STAR" Grounding Assures Signal Purity
and Freedom from Hum & Noise
- High Input Impedance is Ideal Match for Passive Preamps
- Extremely Easy to Install - Exact Size
"Drop In" & Original Terminal Labels
- Can be Operated With or Without Feedback
- Optional AC Balance for perfect phase inversion
- Optional DC Bias Balance to match Output Tube
Parameters
- Optional Polypropylene Capacitors
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| Developing a design that would inexpensively replace the original
Dynaco 7199 design and improve its performance was difficult. Our goal was
to improve the spectral balance and harmonic purity of the original and
preserve the musicality. We have retained the purity and balance of
the midrange while dramatically improving the two weak points of the
original circuit - loose bass and dull high frequencies. We built and listened to many designs including
both classic and modern topologies. We compared all to the original and to
each other and finally settled on a cascode gain stage direct coupled to a
split load phase inverter (as in the original). It is simple and equally
important, met our goals and dramatically improved the imaging and
spectral extension over the original. Surprisingly it retains its
musicality with both standard as well as premium audiophile components
(although the benefits of the latter are evident). While we were designing
the pc board, we included a few optional features that many of you
requested as well including a DC Balance potentiometer (to balance the DC
bias in the output tubes) and an AC Balance potentiometer to perfectly
balance the phase inverter stage. Installation is perfectly straightforward
since the board is exactly the same size as the original including the
exact labeling of the connectors. You simply de-solder the connections
from the original board, drop in the upgrade board, and reconnect the
wires to the same pads. So, within an hour you will be enjoying your ST-70
like never before. Feel free to download our comprehensive instructions to see for yourself just
how easy it is. You may purchase the board blank or fully assembled.
You may also purchase the board and parts as a kit.
Blank Board (PWB-3U) = $67
Board w/ All Parts (KIT-3U) = $110
Assembled Board (ASM-3U) = $140
Driver Tube Option, 3 Premium 6922 Dual Triodes (OPT-V-3) = $48
DC Bal Adjust Option (OPT-DCB-3U) = Add
$12
AC Balance Option (OPT-ACB-3U) = Add $12
Polypropylene Capacitor Option (OPT-PPC-3U) = Add $21
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PWB-S7U "QUAD" CAP MODULE |
PWB-S7U
QUAD Cap Supply |
Schematic
Diagram |
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- Increases Both the Capacitance and Voltage
Rating (to 600 VDC)
- High Reliability Capacitors used with
Resistive Dividers to Protect Capacitors
- Includes Complete ST-70 Bias Supply Circuit
- Includes Original Filter Power Resistors
- Can be Configured for Either Tube or Solid
State Rectifiers
- Extremely Easy to Install - Mounts in Existing
Holes & Uses Original Terminal Labels
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| One of the most frequent failures
in the Dynaco ST-70 is the original "Quad" electrolytic
capacitor. Worse, direct replacements are both expensive and offer no
improvement in reliability. To address this problem, we have designed a
replacement module that contains a composite of high quality capacitors
and will easily mount in the area between the original capacitor and the
rectifier tube (we didn't forget access to the bias adjustments). Our
PWB-S7U module utilizes high quality - high reliability radial capacitors
that will provide many years of service. The composite capacitor array increases
the original capacitance (30,20, 20, 20 to 68, 68, 68, 68) and raises the voltage
rating (500VDC to 600VDC). The original filter resistors are included as
well as a complete new bias supply (diode, resistors, and capacitors). it
allows for either Tube or Solid State rectification and includes the
diodes for the latter choice. Installation is very easy since it mounts in
existing holes (no drilling or cutting) - you simply mount, connect, and go.
You can download our
comprehensive documentation to see how really easy it is. We will be offering the board blank or
as a kit with all parts.
Above Chassis Version
- Blank Board (PWB-S7U) = $29
- Blank Board w/ Parts (KIT-S7U) = $65
- Assembled Board (ASM-S7U) = $98
Below Chassis Version
- Blank Board (PWB-S7U-B) = $29
- Blank Board w/ Parts (KIT-S7U-B) = $65
- Assembled Board (ASM-S7U-B) = $98
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