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In Reply to: 6V6 = Guitar and EL84 = HiFi? posted by Gusser on July 19, 2006 at 17:50:50:
Check out Poinz' creation. You'll find him regularly at the tube diy forum.
Follow Ups:
Much better than the old one. No ads, much more recent data, lots of stuff. Thanks for the reference.
AudioTropic.net Aloha,
Poinz
It's actually on a finished chassis. I need three however for my tube LCR theater system. I also need three KT88 units for the mids but that's anothet discussion.Your design works just as advertised but I want to try some others as well. What about a tuce CCS in place of that 25K cathode resistor? I'll try that tonight with an EF86.
Gus
Try everything.I haven't used a CCS on the tail of the input amp because the 5965 only needs ~3mA/device (6mA/amp) to hit the sweet spot, so a resistor works fine, and is simple. I'm now looking at improved devices for the front end that need 5/10mA/device to rock'n'roll, so a CCS is looking much more attractive to me, as well as ultimately simpler (I can just build the bias supply from Hell, and use it for the tail supply too). I'm not sure the CCS needs to be tube, I have tried several types of resistor, from dirty ol' metal oxides to fab Kiwames in the tail, and could hear no difference whatever , so maybe a pretty quiet chip or discreet sand CCS would be 'jus' as mo'bettah'.
There are places in this circuit that are critical, the tail supply/implementation has proven, so far, to be not one of them.
Mahalo,
Poinz
I was measuring 6.2ma at the 5965 cathodes. No measurable distortion difference between the CCS and the 25K resistor. I was using a 6AU6 and I also regulated the -140 at 150v with an 0A2.Now I really need to get rid of that -150v supply. Reason I am tapping bias voltage from it and the drop to 32volts is too great. I want to keep it at two power tranneys. So tonights test is a solid state CCS using a pair of 2n2222 and an LED fed with -12v. This way I can have a more reasonable bias supply that also feeds the CCS.
I considered regulating the +300 to the 5965 plate loads but with a CCS in the cathodes, it makes little sense, don't you think?
Gus
Gus,One of the reasons we went with self bias in "El Cheapo" was to avoid the hassle of adjusting both CCSes and bias.
Can you "goose" your B+ rail voltage up some? If so, changing from "fixed" to self bias might be beneficial.
Eli D.
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