Here is the the new Bare PCB for Dynaco ST-35 Rev 1 - New Design with EFB circuit incorporated.
The board is similar as the old Shannon Parks Audio SCA-35 design Rev C, and D, that is obsolete.
This PCB also Incorporates the EFB Circuit with LM 237 to keep constant Bias on all 6BQ5/EL84 tubes with just one adjustment.
The PCB was tested 100%, and we have amplifiers built with it sold. We've sold boards to NY, NJ, CA, MI, MN, FL, UK and we keep going! it's been a success!
It uses ½ 12AX7A and
½ a 12AU7 per channel. The 12AX7A is a low noise preamplifier that directly drives
the cathodes phase splitter 12AU7. We also replaced a single cathode resistor
and capacitor with an innovative
Enhanced Fixed Bias feature that allows your ST-35 to perform to its full
potential with both channels driven. The circuit incorporates once for all a
fixed bias operation to enhanced power to its full potential. Audio power will
be maintained with both channels driven and distortion will be significantly
reduced. The regulator LM237 voltage must be adjusted, and test points are
present on the board to connect the VOM and measure 0.27V or 270mV. This is
equivalent to have 27mA running on each cathode of EL-84/6BQ5 throughout each
10 Ohms resistor. We are essentially
setting up the LM237 to delivery +15VDC when measuring its output in relation
to circuit GND. By adjusting the bias, we are averaging the current of four Penthode
EL-84/6BQ5. This means one tube can be on 0.28VDC and the other in 0.26VDC,
resulting in an average of 0.27VDC. For best performance is recommended to have
a well quad matched tube on this project.
This sale here is for unpopulated (bare) PCB.
We are providing a full manual with Schematic, BOM, and assembly instructions. Also, transformer recommended to be used and so on.
This board saves you all the connections you have to do by hardwiring all tubes, besides time and helps avoiding mistakes.
The Black connectors are easy access with a fork terminal will make a nice and clean assembly.
You just need to add Fork terminals to transformer wires and bring it to the board.
The circuit incorporates and Inrush current limiter CL-90 that helps to protect the transformers and amplifier as well.
Save yourself time, money, logistics and researching parts!!! It's all ready to connect your transformers, and plug the tubes.
PCB size is 235mm x 108 mm x 2mm thickness, or 9.25in x 4.25in x 80mils
Material: FR4
Solder Mask: Black
Final Purchase is for 1 PCB unpopulated.
We are going to put for sale the CASE here on Ebay, with top plate cut and beautiful finishing.
You will have option to purchase for DYNACO/EDCOR/HAMMOND Transformer top plate.
Here it's the final product from the board with Hammond case and Stainless still top plate using EDCOR core.
The smooth sound of 17.5W RMS x 2 from the EL-84.
Please BID with Confidence, no returns will be accepted!
Thanks!
MADE IN USA!!
