Audio and Video Talk > Valves / Vacuum Tubes

What Make Valve?

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--- Quote from: Ampdog on July 04, 2016, 04:41:22 PM ---AH!

This is an almost definitive report. As good reports are sometimes indicated, : "Mr Lafferty and Dr Gillespie should be listened to."

If F_D is reading here, I would suggest making this report (including the comments afterwards) a sticky. There are so many tests necessary to define a valve - and then the next batch comes out different! Note that the writers stress that the test batch was limited. As I pointed out before ....  Still, this is one of a very few investigations which highlights important aspects.

I know Mr Lafferty less well, but Dr Gillespie contributes on several forums as a respected authority on valve operation. The man did a lot on valve use even if it is a bygone facility.

Thanks for that reference, Fredeb!

--- End quote ---

A pleasure Ampdog ! I have noticed that with same brand matched pairs , that reading can differ immensely ( from one pair to the next pair - from same supplier ) . Which makes me wonder about valves testing better than 100% ( people state 120/130/140% on Fleabay ) . Is the valve not out of spec then ? ( if tested as , say , 130 % )

>> If F_D is reading here, I would suggest making this report (including the comments afterwards) a sticky.

It be done, Sire!  :)


 Hi All

Has anyone heard or own the EAT cool valves 6922/Ecc88 ? They are uber expensive (R2500 a piece) and wondering if they are worth it or something better out there for the price..


Revisiting previous comments:

The EAT 'cool' valves: ........

Again (as always?  :( ) I am sceptical.  Nothing I could find shows a definite advantage for audio.
  [My favorite phrase, but to be fair it must be acknowledged that 'better' performance under certain extremes often (mostly?) translates to nil for audio. E.g. some shock tests; unless you are going to use your amplifier in an army tank barreling over rocks and through ditches those are irrelevant under home conditions.]

Thus to pay that much more for practically mainly somewhat improved heat radiation; sorry, count me out. Not to re-start another point of contention, but similar hype reigned regarding cryogenic treatment some time ago; died a quiet and welcome death since.

In electronics, to make a rather sweeping statement: The pattern is always roughly the same: A grand term suddenly pops up or is regurgitated, its often imaginary advantages are lauded by the manufacturers (how else), and a small group tags along nodding their heads up and down, confirmation by the wife-in-the-kitchen, the gardener, the family dog (apology to F_D!) .......  To stop there.

Not that improvements cannot still be made particularly with new materials, but somewhat sterner proof is needed than "I tied a knot in my speaker cable and it sounded better."

The working of normal valve testers need also be considered. To my knowledge they mostly use 'pulsed' voltages as in half-wave rectified ones. The steady reading on a meter is then really an integrated "average" of a half wave sweep. Because valves are non-linear this will give different Gm readings than datasheet stats, which are mostly taken at steady-state values of the listed voltage or current (pulsed in case of high values to accomodate dissipation limitations).  That does not imply that a valve tester is useless; given parameter values are often adapted to give realistic results of the valve's condition. But that data cannot be used for design purposes.

Coming closer to Mr Lafferty's and Dr Gillespie's tests: The reading of distortion at high levels is valuable, but a mid-value measurement is also required. Small differences in valve characteristics will cause overload to occur at different points, thus seemingly significant differences could be measured at maximum output, one valve being just shy of overload while the next one is just in it.  As Dr Gillespie mentioned, the sample was too small for measured differences to be tacked onto the brand itself (see the differences found between EH valves under different conditions).

Complex?  Not really, if one just understands what exactly is being measured and what not.

Hi Ampdog

The fact that they advertise the valves  - ( The tube withstands accelerations of 2,5 g at 50Hz for lengthy periods and momentary shocks of 500g for short periods.) I would like to know what the sound pressure would be at 50hz to produce 2.5g of shock. Snake oil?
Ok so being the sucker and skeptic that i am i bought 2 of the EAT cool valves Diamond 6922. Once i got them it did not start off so well. One of the valves had thinner pins than the other and seemed like a softer copper. This caused hissing and popping and thrown the amp into protection mode.. Mailed EAT direct and asked about this as they have such high standards as advertised. They just came back with asking for a proof of purchase and from which country. 3 mails later (not hearing back from them) i contacted the dealer and asked for a replacement. That's 2 weeks ago, the dealer still waiting to hear from the EAT team about the replacement. You would think to dish out 5k for 2 valves the service would be better...
In the mean time i also bought 2 Telefunken 6922 NOS tubes at about a 1/4 of the price of the EAT valves..
Going to be interesting to put them up against each other...that is if i get a replacement EAT valve.


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