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Old 12th April 2012, 08:52 PM   #1
bst is offline bst  United States
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Default Recommendations for 6888 triode operating point?

In the midst of my ongoing parts clean-out, I discovered a bunch of Sylvania 6888 dual-control pentodes. I was about to add them to a bulk sale on an auction site, when I re-read Steve Bench's article on triode-connected 6888s.

Click the image to open in full size.

Wow-- these things are beautifully linear when triode-wired. I began thinking of a small SE amp, or even a White cathode-follower OTL headphone amp. My question is this: How do I determine the best plate voltage, plate current, and output transformer impedance (if any) for a non-standard application like this?

With an Rp of less than 1k, it looks like a 3.5K output transformer would probably be a good choice. But what if I dial back the current, run the voltage up to the limit, and use a 5K transformer? I realize it will put out less power, but will it likely sound better?

Is there a theoretical method to optimizing a single-ended amp design, or is it something, once you determine a normal range of parameters, that is strictly empirical?

Even better, is there someone who has built a triode-wired 6888 amp, and would like to share the results?
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