The Crystal SET amplifier
Crystal SET amplifier project by Martin Thibault
What we have here is an acrylic stereo, 5u4GB tube rectified, Single Ended Triode using two 6L6Gb’s as outputs, one 6CG7 and one 12AX7. It’s powered by a Stancor Power transformer I had on hand, one very beefy Hammond choke, and two 5K Edcor OPT’s which are rated at 15 watts.
This is my first scratch built amp using schematics and assistance provided by:
Of greater importance is the patience and guidance of my very own tube guru, Mike who should be nominated for some kind of electronic sainthood.
He did the math needed to modify the schematic, correctly taught me how to perform the necessary tests and somehow figured out all the stuff I had installed incorrectly. Trust me that this is a gross understatement of the time and assistance he provided.
I also want to add thanks to another Klipsch community forum buddy, TC, who provided and cut the stainless steel bottom plate for me and show me how to make it shine.
Building an acrylic amp has some special considerations: heat and safety.
For this reason I have elevated all tubes and transformers so heat buildup will not warp the case. ¼” acrylic stock was used for rigidity and it also has a higher heat deformation characteristic. Airflow has been added and various spacers and bolts also contribute to rigidity.
For safety reasons, a modern 3 prong safety cord was installed as well as a bottom plate which has attached the chassis ground from that plug as well as the star ground, a feature used to lessen noise.
Layout was important because there are two top plates, the case itself, an extra top for looks and airflow. This part of the project only went so, so since the 12AX7 is probably a little closer to the power supply than optimal, and one of the gain pots had to be added and that hole is off center. Wiring and soldering could be neater, but hey, you’re dealing with an amateur.
I actually employed a color-coded wiring scheme to help me keep track of things and to add some visual candy.
We also changed the original from solid state to tube rectified, added a power switch and pilot light.