| KT120 Class A U/L Mono-Blocks [message #68655] |
Tue, 19 July 2011 20:35  |
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gofar99
Messages: 1947
Registered: May 2010
Location: Southern Arizona
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Illuminati (5th Degree) |
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Hi music lovers, I have been working on a pair of KT120 Push-Pull Class A U/L mono blocks for some time. As soon as the tubes became available I wanted to try them.  Some of you may have seen the amps at the LSAF. Since then I have been tweaking them to get them up to the power they should. Well they now can deliver 45 watts RMS into 8 ohms before going sour. This is great, except the tubes are not as linear as some other members of the KT family. Without using huge amounts of NFB the compromise I reached was extremely low (under 0.25%) distortion at 1 watt, under 1% at 10 watts, 1.5% at 20, and increasing linearly to 4% at 40 watts. The sound is quite good, but not IMHO as good as the EL34 and KT88 Oddblocks. A bit more "clinical" or less warm, than the smaller amps. Then again, for power they can't be beat with any other valve class A design I know of. Large, robust sound. I'll post the revised schematic in few days.
Good Listening
Bruce
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| Re: KT120 Class A U/L Mono-Blocks [message #69375 is a reply to message #69370] |
Wed, 07 September 2011 12:47  |
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gofar99
Messages: 1947
Registered: May 2010
Location: Southern Arizona
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Illuminati (5th Degree) |
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Hi Wayne, The KT120s are quite excellent and sound much better than I ever thought they would. And yes I set up the KT120 amps for use with KT88s. Using the 3.4K transformers the KT88s need to use the 4 ohm taps for 8 ohm loads for best results. This is really no big thing unless you have 4 ohm speakers. When I tested the KT88s in the KT120 amps the results were Superior. The distortion at one watt was at the limits of my gear at 0.05%, 10 watts were 0.33%, 20 watts were 0.9% and 25 (the rated power) was at 1.5%. It just hits 3% at 30 wrms (5 watts over the rating I place on them). That's all good, but the sound while quite excellent, was not as good as in the amps designed for them (the Oddblocks). Now back to the question, no, I think the KT88s are better, mostly because you can choose your tubes, the KT120s have only one brand and type. Perhaps if they catch on things might be different. Does that mean that the KT120 amps are inferior, hardly. They rank right up way near the top for what I have listened to. But my personal favorite remains the Oddblocks with the JJ Blue glass KT88s. Sort of a do you like chocolate or vanilla?
Good Listening
Bruce
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Really not true, but they are hugely powerful and well behaved now. 
