Item Tag: 6 Ohms

Hello Tube Lovers, Here is the the new Bare PCB for Dynaco ST-35 Rev 1 – New Design with innovative Enhanced Fixed Bias EFB™, thanks to D. Gillespie Designs. The board is similar as the old Shannon Parks Audio SCA-35 design Rev C, and D, that is obsolete. The circuit uses a 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! The design was based on Dynaco Stereo 35. 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. The original output stage cathode bias resistor has been replaced with an innovative Enhanced Fixed Bias EFB™, thanks to D. Gillespie Designs, 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 improve power to its full potential. I would like to give full credit here for Mr. David Gillespie on this portion of the circuit since the EFB™ and Enhanced Fixed Bias are trademarks of D. Gillespie Designs. 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 having 27mA running on each cathode of EL-84/6BQ5 throughout each 10 Ohms resistor. We are essentially setting up the LM237 to deliver +15VDC when measuring its output in relation to circuit GND. By adjusting the bias, we are averaging the current of four Pentode 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 80milsMaterial: FR4Solder 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!!

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