Comments for page: 7591A Tube Comparisons

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Posted by Mark September 07, 2012 - 07:39 pm
Thanks, very useful info us tube freaks.

Posted by Steve L. July 27, 2012 - 04:05 pm
Hi JM, Thank you for the kind message!

Posted by J.M. July 27, 2012 - 02:23 pm
Steve: Thanks for freely sharing this info. you guys have worked to produce.

Posted by Dave June 04, 2012 - 10:27 pm
Hi Jamie -- Thanks for your interest and following these tests. Your input alone on the durability of the EH 7591 tubes under band conditions is extremely valuable. Most hifi diyer's don't realize that it is the peak current demands placed on a tube that causes the most wear and tear -- not the quiescent current or current levels required for normal listening levels at home. That your tubes have served you well in a band environment for so long is very encouraging! As we get any new or updated information, we will be sure to add it to the existing data.

Thanks again!


Posted by Jamie Tyson June 03, 2012 - 01:17 pm
I'm happy to see the updates to this article. Again I'll say thanks for putting the time and effort into this testing. I don't use 7591's for hifi applications but I believe my theory of modern tubes applies to both HiFi and guitar amp use- it's helpful to view new tubes as something to be designed around. I'm sure this is frustrating for owners of classic equipment. The advantage of this thinking is that one can view a design with an open mind and appreciate new production 7591's for what they are- usable tonal choices. I've used and abused a pair of EH 7591's for about 5 years of weekly gigging. They've started to sound ratty but at no point in the last 5 years would I say they're bad sounding tubes. I'm happy to see that the transconductance numbers are a closer match for vintage tubes, of course.

Again, thanks for the info!

Posted by Steve L. January 04, 2012 - 05:08 pm
Hi Mike,
Thank you for the kind words. We have considered offering a tube tester product. However, the market is small and there are one or two products out there which may do a decent job of it. There is no great secret to doing proper measurements on tubes. The problem is that all but a few of the testers from back in the day, used very crude test methods. For example, DC supplies were not filtered at all and grid AC levels were too high for meaningful results. Also, power tubes were tested at very low power levels.

We just applied good engineering measurement practices to get accurate results. I guess that we hoped in the beginning, that we would find that classic tube tester results might correlate reasonably with the accurate measurements. Alas, that turned out not to be the case. Hence, we felt it was important to get some information (as crude as it is) out about the 7591's.

Of course, the old adage about the actual operating equipment being the best tube tester, still applies. The measurements we present of actual amplifier performance, demonstrate that.

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