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In Reply to: RE: Some Other Voltage Issues posted by FlaCharlie on July 31, 2016 at 11:47:11
Concerning higher than max ratings, it is true that many vintage amps use 6BQ5/EL84s beyond their design maximum values. Some manufacturers went way beyond these rated voltages and even abused their tubes. The revered Acro 2020 is a great example of this abuse. They did not specify the heavy duty 7189; but, Sherwood did specify the "stronger" 7189.
It is also true that some 7189s were simply "specially selected" 6BQ5s. If you look inside the two types of tubes from the same manufacturer, I bet you cannot "see" any differences between the same mfr. 6BQ5/EL84 vs. 7189.
However, the 7189 is allegedly "up to the task" better than the "normal" 6BQ5/EL-84. Way back when tubes were made in the USA, UK and European plants, their testing and ruggedized proving techniques were confidential; but very significant. If they guaranteed a tube branded a 7189 was a 7189 even though it looked identical to their 6BQ5, their reputation was a big corporate concern. When they tested their tubes, quality control was definitely important. Learning from the industrial grade, mil-spec JAN and Western Electric manufacturing techniques, their proven techniques of "breaking-in" and "endurance testing" tubes were important ingredients. In development and mfr. testing, there is a high probability that a 6BQ5 worthy of enduring 400 Volts continuously, before being branded a 7189, was temperature tested as running cooler than their "stock" 6BQ5. If not, there must be special ingredients that more than meet the eyes. Their reputations depended on their reliability.
For those folks needing heavy duty ability, many manufacturers stepped up their techniques with the 7189A. And, yes, these can "look" identical to their generic 6BQ5s and EL-84s.
When Mike was talking about 25% more power, he must mean his "real time" durability testing revealed better amplifier power output results when using 7189s, not simply instantaneous results. Unless you have a huge stock of 6BQ5s, why push a 6BQ5 beyond their limits when the 7189 can easily endure more torture ?
Follow Ups:
IT,
In addition to the important points you raised, consider money and economies of scale. If, for whatever reason, reputable tube maker X had to produce 7189s, a quantity greater than that needed to fill a contract, etc., would be constructed, with the "excess" being sold as 6BQ5/EL84s.
It's both ethical and legal to deliver a product that exceeds specifications, as is the case of 7189 vs. 6BQ5. If doing so was profitable, you can bet that some tubes sold as 6BQ5 were really 7189. However, you can't count on any particular NOS 6BQ5 specimen as being a 7189. Date code research of 7189 production runs might provide an indication.
Eli D.
"When Mike was talking about 25% more power, he must mean his "real time" durability testing revealed better amplifier power output results when using 7189s, not simply instantaneous results. Unless you have a huge stock of 6BQ5s, why push a 6BQ5 beyond their limits when the 7189 can easily endure more torture?"
Actually, I believe I read a post by Mike in the archives that said he had measured his S-5000 at 1000 Hz, and I think it was a steady output, not a momentary peak. But, as I said, 25% only equates to an extra .75db, so really not much to be gained in sound level output. Measurable, yes, but probably unnoticeable in a typical listening situation.
I don't doubt the 7189 responds better to "torture". Would you characterize running a tube rated for 12 watts plate dissipation at only 10 watts as "torture"? If the tubes aren't being run over 12w dissipation my guess is that either tube should be fine. I do have quite a few NOS American BQ5s - mostly GE, RCA and Sylvania.
Like a jackass I sold two of my NOS/NIB quads of Syl 7189 black plates for 115.00 each quad..This was in 2006 tho..
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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