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RedRoo Lives

For years I've been mucking around with valve amplifiers, much to the amusement of my family and friends. My first attempt was a version of what's called the Murray amplifier; a 20 watt per channel design by Australian Cyril Murray in the 1960's, which used 6CM5 television line-output valves. I used PL509 valves for a bit more power. Cyril Murray went on to build amplifiers for the Sydney Opera House and his work was very well respected. 

Later I made a 60 Watt 'circlotron' design using four triode connected KT120's in each channel. The circlotron is a fully balanced cross-coupled power supply design which has the advantage of a very low output impedance; enough valves and enough negative feedback and it will drive a loudspeaker directly without an output transformer. I used a fairly low turns ratio output transformer mounted at the loudspeakers - for some voltage isolation for my VAF-i66 speakers, less output valves, no negative-feedback required, and no need for expensive speaker cables. See the photo below. 

I still use the circlotron amplifier when I need some power, but it's a real room warmer, so for everyday listening I built the RedRoo 5 Watt Class-A design which is now offered in kitset form. It's a great little amp, and I actually prefer the sound to anything else I have for casual listening. I tested the kit-set build on my family and friends, and every amp they have built works perfectly.

Whichever way you look at it, valve amplifiers are expensive - even as a kit-set. However, you can also buy the Information Pack which includes a quality 2mm thick fiberglass PC board and all the information you need to source any components you don't already have, and build the amplifier into your own case. You will also get a $75 discount off the price of a full kit-set when it is available, (which won't be too long, and would certainly be a lot easier).

I'm sure you will have as much fun as I have building the RedRoo amp. And remember, we need lots of happy customers, so we are right there to help you. Please let me know what you think about this project and the website.

Phil Wait
RedRoo Kit-Sets
Sydney

p.s. As I write, the full kit-set is not yet available as we are in the last stages of organising component and metalwork supply. I expect them to be available in October 2019,

60 Watt per Channel Circlotron Amp.

60 Watt per Channel Circlotron Amp.
The Redroo 5Watt Kit-set Amp.

The Redroo 5Watt Kit-set Amp.


 

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