Comments for page: 7591A Tube Comparisons

<<first - <previous - 1 - 2 - 3 - 4 - 5 - 6 - next> - last>>

Posted by Richard Sherman October 07, 2011 - 05:15 pm
Thanks for taking the time to analyze the current production 7591 tubes. I have been consistently disappointed by these tubes and your results indicate they are at best a close approximation to the real thing. I survive with 6GM5's and watch $400 quads of NOS Sylvanias on Ebay go by with no bidders. We are paying for devices that like a bouquet of flowers, will wither with time and fail after hours of use. The proof is almost always in how a tube performs in a real amplifier versus a tube tester. Your findings with the EH 7591A are the same, the tube does not have the smooth sound of a real 7591A. The JJ tubes in my amps just turned cherry red and one lost it's vacuum after 10 hours of use. All in all to date, no one has been able to equal the real 7591A. I am waiting for that moment to arrive.

Posted by Steve L. September 19, 2011 - 09:41 am
Hi Rob,
I really appreciate your kind words. ---Steve

Posted by Rob September 19, 2011 - 09:30 am
Thanks for posting this info. It was very helpful in deciding if I could trust New tubes in my guitar amp. The EH's are probably the best for this application since distortion in a guitar amp is not necessarily a bad thing.

Posted by Steve L. June 24, 2011 - 01:44 pm
Hi Jor, Thank you for your comment but actually, that is mentioned in the last item of the Conclusions list. (Easy to miss.) I do appreciate your citing the Fishers, since we mentioned only the Scott LK-72.

Posted by Jor June 24, 2011 - 12:31 pm
No mention that the eh's are huge compared to the others! And don't fit in Many amps. Especially old fishers

Posted by Steve L. April 22, 2010 - 10:06 pm
Bud, I noted in several places in the article that the results are of limited scope and that the Hickok data are not very good indicators of actual power tube performance. We put little credence in the Hickok data, by itself, even though it is one of the best commercial testers known. However, the fact that the EH 7591 tubes read less than half the strength of NOS tubes, while the JJ's do much better, gives rise to a little concern.

When I looked for real measurement data on the Web, little was to be found. Faced with having to buy 7591 tubes, Dave and I had to make what measurements we could. We thought that we should make that information available to others.

The Eico amplifier performance data represents real-world conditions of the typical use of these tubes which many people might encounter. As such, the results showing the weaknesses of the new manufacture tubes are significant.

Dave's custom-built power tester draws on his extensive experience in building tube amplifiers. It is a highly accurate indicator of the maximum power that a tube can deliver. So the data he provided from that is quite sound.

I'm sorry if you happen to be a seller of any of the tubes which didn't fare well in the tests. I can only offer you the opportunity to provide data of your own to refute the findings presented here. Actual measurements of a good product would be a more effective way of making your case than hurling invective at those who are only trying to uncover the facts.

Posted by David Gillespie April 22, 2010 - 06:25 pm
Bud -- I'm not sure why you find the "tests" flawed, misleading, and full of nonsense. They simply tested various brands of 7591 tubes in various situations. That would seem like a useful test to me. The results are accurate and repeatable, and based on traditional standards of distortion and power output. How does that make them flawed or full of nonsense? Since you offered no specific data to refute the findings, I can only assume you simply did not like the outcome. The fact that you get five different readings from your five different testers is in part the very reason for the tests. A Gm test by Hickok or any other similar tester relates very poorly to real world results, as the tube handles only a fraction of rated current flow under that type of test. On the other hand, power and distortion measurements relate quite closely. Also, you did not state why 7591s "do best" at 25 mA idle current. This may be good for tube life, but I can assure you that all measured distortions will be seriously elevated at that level, and power output will suffer as well. Maybe you could provide some detailed data to support your position, and post it here for review?

David Gillespie

Posted by bud April 22, 2010 - 07:49 am
while your "tests" appear to be helpful, they are not. You can not mix apples and oranges and get any real valuable conclusions. As for the Hickok tests, every Hickok model will test these tubes differently, some Hickoks will test them as if they were a 6l6 and some as a 7591. I can take the same tube and put it in 5 different Hickok testers and everyone will give a different value for the same tube ( they are all rebuilt and claibrated) and that goes for old stock and new stock too. Your Idle current is way to high, these tubes do best at idle no higher than 25ma. Last point, I would like to see you identify .1% vs 1% distortion in playback. Your total review is badly flawed and misleading, and draws conclusions based on nonsense.

Posted by Steve L. March 22, 2010 - 08:10 am
I really appreciate your comment, Jamie. --Thanks, Steve

Posted by Jamie Tyson March 21, 2010 - 11:33 pm
thanks for the article, great info!

<<first - <previous - 1 - 2 - 3 - 4 - 5 - 6 - next> - last>>