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In Reply to: RE: Grant Fidelity/Psvane tubes posted by Bob Olson1 on February 24, 2014 at 07:02:58
I am not affiliated with Grant Fidelity in any way - I am actually a competitor.But I need to get started on correcting a VERY common misconception...
The fact is ALL tubes are microphonic to some degree. Even tubes that don't produce audible sounds when tapped (more on that in a moment) produce microphonics you can see on test instruments. That is 100% totally normal.
Here is the key point - JUST BECAUSE A TUBE MAKES A NOISE WHEN YOU TAP IT DOES NOT MEAN THE TUBE IS EXCESSIVELY MICROPHONIC!!
All Grant can do is test to see if a tube is excessively microphonic. It's the same for me - I will gladly replace a tube that is excessively microphonic. But because a tube makes a noise when you tap it does not mean it is excessively microphonic.
If I may, I'd like to quote from another one of my competitors, Upscale Audio/Kevin Deal. Here is what he says about microphonics:
"Okay...listen closely class, because I will say this only once: DO NOT TAP ON TUBES! You can permanently damage them! Repeatedly tapping on a tube's glass can cause a perfectly good tube to become too microphonic for use.
ALL tubes are microphonic to a greater or lesser degree. Whether or not that microphonics is audible will depend more on the tube's function in the product, rather than the microphony of the tube itself. In some positions, you will never hear anything, even with the worst tube. In other positions you will hear something even with the best tubes. At that point you make a judgement call: does this level of microphony interfere with my listening enjoyment?
Tubes are supposed to make noise when tap you tap on them! If a tube is truly microphonic, and in a position where it is critical, you will know it. It will feedback as you play music and be so objectionable you'll turn it off."
Allow me to add to Kevin's well written note - if you tap (VERY carefully!!) a tube and you get a sound that stops as soon as the tap is over (immediately or nearly immediately) that is a tube that is NOT excessively microphonic. Excessively microphonic tubes will sustain the noise for a good bit before stopping or will make the noise indefinitely. A few tubes - like the 6922 as an example - will behave somewhat differently and can't be judged the same way, but for most that's an appropriate rule of thumb.
Your fingernail tap test did not indicate excessively microphonic tubes if the only thing you heard was a noise when you tapped. I'm surmising that Grant Fidelity replaced the tubes just because they wanted to take care of their customer by going the extra mile.
If you'd like to learn more about it I recommend an EXCELLENT book the link to which is below. Chapter 3 deals with "Subjective Failures" - or if you want to read more about just microphonics look at page 48.
Too many fine quality tubes are being condemned because of normal microphonics.
Edits: 02/25/14Follow Ups:
Jim, it said "Not Found" when I tried to access the link you included.
I hear what you're saying about not banging away on the tubes to "detect" microphonics, and I always tried to use a gentle tap, preferably with a pencil eraser, before getting the George Kaye unit.
I wound up testing a bunch of the 9-pin tubes in my "stash" and was amazed at what the Kaye tester told me. Even a few of the supposedly super-quiet Sovtek 12AX7LPS were not nearly as quiet as advertised.
The link is fixed, sorry!
Seriously, for those of us who don't know triodes from tricycles and whose eyes glaze over at the very mention of anything "technical", your points about microphonic tubes are all well-taken. And agreed with. And not just because I don't know any better.
I keep harping on the Kaye tube checker because it's clearly a "tube tester for dummies" and yet it seems to do things the others don't. My other tester, for instance, an Eico 667, is virtually worthless to me. Except for telling me a tube is dead, which I can pretty much tell by other means.
See if this makes sense to you, from the Kaye tester's operating manual: "The feature that sets this tube checker apart is the ability to listen to noise and microphonics while the tube is functioning in the typical class A circuit. You can perform noise and microphonic evaluation, test the gain of the tube in the circuit and compare and match tubes. Maximum output before clipping is tested."
BTW, I did read, or tried to, all 160-odd pages of the linked tome.
Dave,
You wrote:
See if this makes sense to you, from the Kaye tester's operating manual: "The feature that sets this tube checker apart is the ability to listen to noise and microphonics while the tube is functioning in the typical class A circuit. You can perform noise and microphonic evaluation, test the gain of the tube in the circuit and compare and match tubes. Maximum output before clipping is tested."
Yep, that works for me. That's what the VTV unit does except for testing the clipping point. The Amplitrex can be programmed to do a similar test and much more (as well as listening to a tube). And the Maxi gives a readout of actual noise voltage in db below .775 volts across the audio band as well as letting you listen to the tube. So you and I agree - it's GREAT to have test gear that does something useful!
Now, since you've read the book, see if you can't find posts that give you a chance to apply what you read - or a reason to go back and re-read it. Watch how much you pick up!!
I put Bob Olsen's Psvane 12AT7s on mine and three of the four of them howled like banchees. Didn't need to touch them, just increase the tube checker's volume level a little and listen. Detecting an overly noisy and/or microphonic tube is simple with the Kaye unit. Yes, there are varying degrees of microphonics and it can tell you just how microphonic a tube is.
Dave,
That was not stated in the original post, so I had no way of knowing what else occurred. Maybe Grant Fidelity wasn't being as magnanimous as I thought...
I have 3 devices to check for noise/microphonics - the VTV Vacuum Tube Characterizer, the Maxi-Preamp tester, and the Amplitrex AT-1000. Those devices (and some headphones for the Maxi and Amplitrex) can indeed do a good job of detecting excessive microphonics.
But that was not my point. My point was that often a tube will get condemned because it makes a brief noise when tapped (because ALL TUBES ARE MICROPHONIC to some degree) which is entirely 100% normal.
Also, PLEASE read the Tomer book section I mentioned. Because as I mentioned before in my quote from Kevin Deal, the susceptibility of a tube to displaying excessive microphonics is dependent on
a) the environment in which the tube is operated, and
b) the circuit in which the tube was used
Tomer explains this VERY well, it's a terrific book - and it's free in .pdf form.
Jim, you are correct as usual. There have been recent posts on other forums about tubes, the expensive Holland EL34 copies, and others failing prematurely. They were not purchased from Grant. No endorsement, just a fact. If you buy these tubes, know your seller and be sure the warranty will be honored.
Edits: 02/24/14
My main point was the how widely misunderstood the whole microphonics issue is, and that we get a handle on it. At some point the cost of replacing a lot of perfectly good tubes due to this misunderstanding does impact the purchase price we all have to pay!
Yes it does and a small amount of microphonics make tubes..sound like tubes. I check it with a ball-peen hammer....just kidding. :-)
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