I received a request from a friend who want a 2A3 SE amplifier. Here’s the 2A3 I build for him.
I used 6E6P as driver stage. The 6E6P are long life military tube which is very linear when connected in triode mode, Rp are around 1.2K , suitable for use as driver stage. The gain are around 25+ when using plate choke as a load.
I did some test on most of output transformers in market, either they are too expensive , or not perform well. Thats why most of output transformers / chokes in my DIY vacuum tube amplifiers are hand wound by myself, so that I can take control of quality or suitability of impedance / characteristics etc. I will write a separate post on how to wind an output transformer soon.
For plate choke, I choose 0.35mm CRGO EI66 material stacked to 32mm thick . I wound 5000++ turns in total , all 36 layers with thin paper in between, and leave air gap on EI core using craft paper. It measured around 60H , good enough for 6E6P plate load.
Each 6E6P biased to 2.4+ V at its cathode to get 27mA plate current, and the supply at plate choke measured around 150V.
The power stage is just a classic self-biased 2A3 stage. I’m trying to use filament bias but since my friend refused to put any transistor or mosfet in his tube amp, I used normal DC supply for filaments.
For output transformers, I built a pair of C core transformer for this amp. C core output transformer consist of two identical windings, with each side of 4 sections primary and 3 sections of secondary, all primary are in series and secondary are in series-paralleled.
I love wood frame chassis and apply beeswax on plain wood for natural look. top and bottom plates are aluminium painted in red.
As for listening test, I played several type of music, this 2A3 SE amp is much differ from my previous 6SN7-2A3 or 717A-2A3, the plate choke can really store energy and I get more detail, very dynamic, very satisfying bass, and huge soundstage.
Here’s my ugly hand drawn schematic diagram:
A short video here with Fourplay “Chant” :
Here’s another test by request from a few from forum friends, female vocal ( Chinese, because youtube deleted most of copyrighted songs )
I’m waiting for my external microphone, once I received, I will record a video clip again and post it on my youtube channel.
Please subscribe to my youtube channel for more video:
Stay tuned !