Hi Brian. Second harmonic performance isn't too shabby from the RCA plate curves. An excerpt for a 40kohm load below. On casual inspection it doesn't look worse than, say, the ubiquitous 12ax7. Better audio tubes, known and unknown, are undoubtedly available. In this application the 5964's major disadvantage though appears to microphonic. It otherwise measures very well and if last's night mono session was any indicator, sounds great in this circuit too.
However, I agree something like the 955 or 9002 make for better examples of the principle, potentially terrific audio tubes heading for the crusher for being unknown.
Edit: Loadline shown at ~6.25 ma for ease of judging linearity, I run it at ~5.5 ma.
However, I agree something like the 955 or 9002 make for better examples of the principle, potentially terrific audio tubes heading for the crusher for being unknown.
Edit: Loadline shown at ~6.25 ma for ease of judging linearity, I run it at ~5.5 ma.
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I lucked into a several pieces of digital tube gear, digital counters of fairly recent vintage by tube standards, to be specific. These are loaded with computer-type tubes. Most check good on the analyzer. I will be playing more with these types when I have more time.
It's worth it. The results I mentioned earlier shown below, hot off the press. Overbiasing the 7591's causes the 3rd to plummet below the 2nd, so I'm confident it's not generated by the driver or by 2nd order cancellation between driver and output. The circuit is a simple LPT driving a P-P output, unused driver input tied to ground. This tube has the potential to be killer in something like an EL84 p-p.
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