Author Topic: JJ E88cc and Amperex white label Bugleboy Ecc88/6DJ8  (Read 998 times)

Offline steve

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JJ E88cc and Amperex white label Bugleboy Ecc88/6DJ8
« on: May 26, 2017, 10:02:59 AM »
An audiophile friend of mine gave me a pair of Bugleboy Ecc88/6DJ8 tubes about 6 months ago. Can't even find them listed this way. I already have many Amperex white Bugleboys from Holland out of very old Tektronix oscilloscopes, but my white Bugleboy 6DJ8s/E88ccs sound different.

For about 6 months, I have been investigating the difference between the JJs and these Bugleboys. The JJs, in a preamplifier circuit have about 18/19db less total harmonic distortion (THD) than any ^DJ8 or ^SN7 family, under single ended 2 volt rms conditions.

A better perspective, whereas the ^SN7 and ^DJ8 family of tubes produced about 0,1% THD, the JJs produced approximately 0,011%. Another way of putting it, the former's THD was approximately -60db down from the fundamental, the JJs were approximately -79db down.

So how did this difference play out in my monoblock amplifiers? After performing listening tests for months, I found I could adjust my zobel resistance much more with the Bugleboy with virtually no sonic difference while the JJs were so touchy, virtually any change in the resistance was perceived.

What are the conclusions we can deduce from my experiments?

1. It is much easier to design using the Bugleboy ^DJ8 or ^SN7 family than the JJs. Parts quality or quantity is not so critical as the harmonics tend to give the music a richness.

2. However we have a two edge sword. The richness of some ^DJ8s, ^SN7, and I am sure other tubes produce a "signature" sound, so a little less accuracy. A little masking is occurring. The music will sound a little different.

I could adjust the JJs for a nice rich/fleshy natural sound. The settings were just slightly difference.

3. With that said, all components, including speakers, need fine tuning adjustments. Speaker placement is also very critical.

I was adjusting the Zobel resistance, very easily less than 0,1 ohm out of 800 ohms. If I adjusted the resistor across the full range driver (not the zobel), it was easily less than 0,1 ohms out of approximately 9,000 ohms. Speaker placement changes was to less than 1/16 inch for perceptibility.

I feel like the movie, Fiddler on the Roof, going back and forth with pros and cons.

In conclusion, it did indeed take some work. I believe the experiments also provided valuable information for the general public. The ear is more sensitive to tonal balance/frequency response deviations than we believe.

Cheers
Steve
« Last Edit: May 26, 2017, 10:12:11 AM by steve »
Steve Sammet (retired, but manufacturing "V" ics again)

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