Shiny Eyes by Radu C. Tarta

This is a fantastic 4P1L push pull incarnation done by Radu. I hope you enjoy reading this post as much as I did. Cheers, Ale

Introduction

“Shiny Eyes” Push-Pull tube amplifier is the result of 6 months of research, experimentation and lots of music listening. It started in the summer of 2012 when life opportunity re-opened the door of an old passion: electron tubes. However, this time my goals were directed towards audio. I understood from the beginning that after 30 years of interruption I have to dedicate a great amount of time and energy to catch up with technology and ideas. I want to thank my wife Paula for her emotional support and understanding. I am also grateful to the fanatics from the DIYaudio community for their contribution to the world of tube audio experimentation. Personal thanks to Kevin Carter of K&K Audio for his advises and help, to Ale Moglia of Bartola Valves for his inspiring work and to Rod Coleman for his excellent filament regulators.

Initial tests

Here are few images taken during design, experimentation and final building: Early stages…

Here is the top plate CNC-ed at high quality by ProtoPanel

Earth bond

Loctal sockets for the 4P1L

Wiring the amp

Testing

Finished amp without transformer covers

Final build and design notes

Design goals:

• pleasure our senses
• not trying to measure perfect, but make it sound warm and transparent
• zero global feedback
• 2 stages design, 4П1Л DHT triode strapped for final valves
• minimum number of capacitors in the signal path
• quality components in a reasonable budget

Schematic description:

• played with different final stage tubes(6P3, KT77, 6C41, 4П1Л) and driver stage tubes(6S3P, 6C45P, 6H6,6E5P,6H30P) and loved the sound of 4П1Л and 6H30П-EB.
• 4П1Л filaments powered from a separate dual bobbin transformer, 11V raw supply and Rod Coleman’s regulators ( one for each channel)
• 6H30П-EB filament DC powered
• lots of Lundahl iron: LL1649 main, LL1638 Choke in special configuration for improved common mode rejection, LL1663 as OT, LL1660/10mA Alt “V” as IT
• bridge rectifier using UF5408 ultrafast rectifier and filtering capacitors are Clarity Caps TC series 110uF
• Delay HT 60 seconds based on 555 IC
• Final stage parallel 4П1Л (4X 4П1Л) filament biased, operating point at 245 V, 35mA, -21V ( tubes were selected to match as close as possible
• Driver stage  6H30П-EB balanced and cryogenic treated(tried also the standard version but liked the sound of the cryo better(more depth)), cathode biased, operating point at 120V, 25mA, -5.5V
• Elna Cerafine for cathode caps and Takman for resistors in the signal path except the final stage cathode (filament) resistor which is wire wound chassis mount
• Wires in the signal path are Teflon silver plated ( just had them and try to give it a shot, but I didn’t hear any noticeable difference in sound. However, I like to work with Teflon isolation)
• ground wiring is a combination of star and ground follow signal

THD measurements

• Gain 17dB (7.3X)
• Maximum power before clipping:  7W
• When 1Vrms input signal, 6.7W power output @ 0.2% THD

N.B. Measurements were done repeatedly under the same conditions, however high accuracy and precision was limited by measuring tools used. To measure THD I used ARTA software and USB external sound card EMU0204 and a attenuator interface( THD of sound card and attenuator at -17dB position was 0.025%) to protect the sound card. To measure and visualize output signal a Rigol DS1102E digital oscilloscope was used.

Listening impressions

• vocal sounds amazing, transparent and warm
• instrumental sounds well defined, full of depth and great separation
• sound is amazing for jazz, classical and vocal

My setup is: Marantz CD5001 player and Klipsch Synergy B3 speakers

Final Note

This amplifier will come soon at www.simplepleasuretubeamp.com:

I am working on a documentation for my amp, and I am hoping on performing more accurate measurements. However, this amp’s sound can better tell the truth.

Hope that you enjoy seeing a finalized amp with the amazingly linear Russian 4П1Л.

Best regards,

Radu Tarta

Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp) View all posts by Ale Moglia