Comments for page: 7591A Tube Comparisons

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Posted by Mike January 04, 2012 - 04:29 pm
Your data is MUCH appreciated simply because there is next to nothing on the 7591 tubes. If your tester engineering is so much superior to Hickok's why aren't you selling it? I've always understood a testers "GM" to be relevant and taken with a grain of salt. The 752a I own does fine for me.

Posted by Steve L. October 25, 2011 - 12:47 pm
Hi Mo, Looking closely at EH's pictures of the 7868 and the 7591, it does indeed appear that they are different. In any case, our article is focused on tubes with the 7591 pinout and the 7868 would, of course, require rewiring. Nevertheless, I appreciate your bringing up the fact that EH uses a different structure in the 7868.

Posted by Mo October 25, 2011 - 11:40 am
Steve- when you hold the EH7868 side by side with the EH7591 you can physically see that they are a different size internally. Unfortunately I can't attach a photo.

Posted by Steve L. October 21, 2011 - 08:46 pm
Hi Mo,
The original RCA 7868 was just the 7591 with a different pinout. Looking at the EH version of the 7868, there is no apparent difference in the internals, versus their 7591. What makes you think that the plate structure is different?

Posted by Mo October 21, 2011 - 05:08 pm
Too bad you didn't include the EH-7868 in your test. These have a different plate structure than the EH-7591's. I use these in my Fisher 400 and they sound better to me than the EH-7591 that I'm running in a few other amps.

Posted by Steve L. October 18, 2011 - 08:19 pm
Hi Butter, Thank you for the kind post and for the DIY fix on making the JJ pins fit. Yes, I imagine that acoustic feedback really would degrade sound quality. Sorry that the one Sylvania developed microphonics. However, you might find a hifi amp owner that would want the pair. Microphonics would be far less of a concern in that kind of application.

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