TRIODE HI-FI & RELATED TOPICS, MOTORCYCLES AND STEAM POWER.
Hello, I'm an expatriate Brit, now naturalised American living in North Carolina, USA. I left the UK when I was offered a job here. I have tried to make the project presentations both informative and useful. I hope you not only enjoy browsing my pages but find something helpful. Please pass my URL to anyone whom you feel might be interested, Thanks.
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August 2009; I have been mulling taking the isolation of audio circuits to a new level and this connected with a desire to build a 50 amp that would permit fixed bias with a 50 DHT with no possibility of grid-current induced failure. In taking full advantage of what I have learned about current regulators with the 6AS7G update, what resulted is an amp that can be simply switched for either 50s or 300Bs and that can drive the 50 into Class A2. 3.5W @2% and 7W @ 5% with lovely free, agile and articulate sound. My best to date.
While making mechanical modifications to reduce microphony, following the success with the new 50-300B constant current topology, I took the opportunity to modify my line-stage similarly, also to install a 4 section Goldpoint Mini V switched series attenuator.
Failure of this lovely sounding and inexpensive design caused me to take a hard look at constant current sink design. What emerged may not surprise you, however I did not expect to see such worthwhile performance gains, especially in respect of stability of DC current with respect to impressed voltage.
I bought a nice looking cheap Chinese amplifier that basically did not work. It became a fun learning project, especially working with the difficult characteristics of the cheap output transformers to get solid stability into reactive loads. In what may be a unique first, this is the first Hi-Fi amp I have designed/built that does not feature regulation on all the rails!
I got inspired and updated this to use a cascode CCS to balance the signal current in each cathode follower pair, thereby minimising signal current interaction with the B+ supplies(s). I have deleted the B+ voltage regulator and separated the supplies for each channel.
I replaced the output stage (5842) grid resistor with a choke to ensure DC stability at high current.
I got carried away and developed a 10k double C core output transformer for the 845 SE. I tried two configurations and several thousand feet of copper wire before I was satisfied. Go on take a look, unlike masturbation (makes you blind) transformer winding really will ruin your eyesight!
Just a Thought:
"Dear God. I pray to remain centered in your love and free of fear so that I may have the strength to do those things that I know I should and to behave as I know I should. I pray that all sentient beings be filled with loving kindness and that all sentient beings be at peace. Amen "
First published: 5/30/2001. Contents of this site are © Richard F Sears, All rights reserved. The only non-copyright contents are any public domain data and the "Amazed Bear" and Mallard on Ribblehead Viaduct photographs.