VT1000: Can I Trust the Results?

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stratlover1964
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VT1000: Can I Trust the Results?

Post by stratlover1964 » Fri Nov 22, 2013 5:43 am

Greetings Orange men (and women) :D

I've been waiting months for the VT1000 to finally land here in Australia and I finally got my expectant hands on a unit which shipped to me last week. I'm now questioning the results, just like another poster here.

A good friend of mine is a valve collector. In fact, he has 1000s of them but has very little use for guitar-style valves. I've been able to take around 100 of them from him on approval ($5 each, regardless of size / type). The valves are all either new old stock (in boxes) or scavenged from various appliances and garage sales over the years. All of them are from the 50s and 60s and are British, German, Australian or American.

My concern relates to lower gain pre-amp valves. My collection includes Philips, Telefunken and Mullard 12AX7, 12AU7 and 12AT7s.
  • I tested 24 12AX7s: 14 good, 5 worn and 2 failed. Ratings varied from 4s to 10s both triodes
    I tested 23 12AT7s: 12 good, 8 worn, 1 failed. Ratings varied from 2s to 9s, both triodes
    I tested 26 12AU7s: 3 good, 1 worn, 21 failed! Ratings for the failed valves 1s, occasionally 1 and a much higher number, though this changes, oddly, when re-testing.
Aside from the statistical unlikelihood of the above, I've already verified many of the 'failed' 12AU7s in V1 and V2 positions of my Bogner Shiva and not one of them exhibits a problem.

The unit I received was supposed to be brand new, but had some cosmetic marks on the case I suspect it's taken a knock. To their credit, the supplier has agreed to either refund my purchase or replace the unit with another brand new one, although it'll take a week to get to me.

Anyone else had issues testing known good 12AU7s with this unit? Or have I just hit a rich seam of duff valves purely by chance? Your responses might make me rethink the results I've had for the other valves and the EL34 / KT66 / EL84s I've tested with it...

Thanks in advance for your thoughts.

jontheid
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Re: VT1000: Can I Trust the Results?

Post by jontheid » Fri Nov 22, 2013 4:53 pm

I think the most worrying thing from your post is that results can vary significantly when retesting the same tube.

When a tube fails, does the unit give you any idea of why it has failed?

stratlover1964
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Re: VT1000: Can I Trust the Results?

Post by stratlover1964 » Fri Nov 22, 2013 9:01 pm

No. This unit is designed for non-technical operators. It only explains IF a valve fails, not WHY it did.

The results vary by around 5% each time when re-testing other tubes, although the manual explains that the unit has been calibrated for cold tubes, so warm ones will result in variation.

Anyone else been able to verify tests of 12AU7s with this unit?

stratlover1964
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Re: VT1000: Can I Trust the Results?

Post by stratlover1964 » Tue Nov 26, 2013 9:20 pm

The supplier has agreed to replaced the unit in case it's faulty. I'll update my post when the new one arrives.

Orphin
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Re: VT1000: Can I Trust the Results?

Post by Orphin » Fri Nov 29, 2013 8:04 pm

I have a VT-1000 a I did write a review on about it when I got it. It's posted on this forum somewhere. I think I recall mentioning some wierd things about it as well..?

Anyway. I do have a pair of Philips EL84 that worked fine in the amp, but when I tested them they both failed in the test. I haven't tried them in an amp since then. God knows what made these specific tubes to fail??

Matching tubes seems to be working very good though.
David
I'm speaking out of my a$$. Yours might differ.

stratlover1964
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Re: VT1000: Can I Trust the Results?

Post by stratlover1964 » Mon Dec 02, 2013 8:09 pm

Update. My replacement unit arrived yesterday. So far, I've tested 7 12AU7s that were previously failed. The results?

4 tested good
1 tested worn
3 tested fail

I'm also retesting each valve several times until the temperature rises and the rating stabilises (tends to rise or fall with each test before plateauing).

Verdict: my original tester was faulty. I'll retest my entire collection and if anything unusual occurs, I'll post it here.

a.hun
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Re: VT1000: Can I Trust the Results?

Post by a.hun » Mon Dec 02, 2013 9:45 pm

(VT1000 PDF manual) wrote: Carefully insert the valve into the correct valve socket and ensure it is seated flat.
 Valves must be tested at room temperature.
 Testing a hot valve may result in a failure as the tester is calibrated to heat the valve up as
part of the test sequence.

If I re-test the same valve the readings are slightly different, is this ok?
The VT1000 uses a complex algorithm which analyses the many different tests which are
automatically performed. In order to keep the total test time to a minimum, the unit is calibrated at
manufacture to test cold valves. If a valve is subsequently re-tested while still warm, then a slightly
different reading may be observed. There is nothing to be gained by re-testing the valve as the glass
envelope will become hotter and increase the length of time before it can be safely removed.
...


Andy.
aNDyH. :wink:

Ever tried to outstare a mirror?

In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!

jontheid
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Re: VT1000: Can I Trust the Results?

Post by jontheid » Thu Dec 05, 2013 7:42 pm

I can't quite get my head around a valve tester that tests the valves cold.
I would have thought that valves would only be in spec once properly up to working temperature.
AFAIK all the datasheets give readings for hot valves.

Orphin
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Re: VT1000: Can I Trust the Results?

Post by Orphin » Fri Dec 06, 2013 9:28 pm

The tubes will get hot during the test though, but I see what you mean.
David
I'm speaking out of my a$$. Yours might differ.

a.hun
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Re: VT1000: Can I Trust the Results?

Post by a.hun » Sat Dec 07, 2013 7:23 pm

jontheid wrote:I can't quite get my head around a valve tester that tests the valves cold.
I would have thought that valves would only be in spec once properly up to working temperature.
AFAIK all the datasheets give readings for hot valves.
How long would you gave them though? In theory they are working 'properly' after about 30 seconds, no?

(Yes! :wink:)


Andy.
aNDyH. :wink:

Ever tried to outstare a mirror?

In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!

jontheid
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Posts: 821
Joined: Sun Nov 02, 2008 1:05 pm
Location: London, UK

Re: VT1000: Can I Trust the Results?

Post by jontheid » Sat Dec 07, 2013 8:21 pm

Well, yes. If the tester let the valves warm up for a bit and then tested them I could understand it.
Then it wouldn't make any difference if the valves were warm already.
The fact that the manual states you can't use warm valves means that the valves are being tested before they reach operating temperature. This is the bit I can't understand. How does a tester know that a valve is good or bad before it has even had the chance to warm up properly?

a.hun
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Joined: Sat Jun 15, 2002 1:05 am
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Re: VT1000: Can I Trust the Results?

Post by a.hun » Sun Dec 08, 2013 10:39 am

Thought it took a couple of minutes to test each valve. I really don't know, not pretending otherwise, but I'm not sure I see a real problem. I'd guess for consistency (level playing field) and ease of use (quickness) the VT1000 tests them as they ramp up and start to dissipate.


Andy.
aNDyH. :wink:

Ever tried to outstare a mirror?

In the bathtub of history the truth is harder to hold than the soap, and much more difficult to find!

jontheid
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Posts: 821
Joined: Sun Nov 02, 2008 1:05 pm
Location: London, UK

Re: VT1000: Can I Trust the Results?

Post by jontheid » Sun Dec 08, 2013 12:46 pm

Yeah I'm not saying it isn't any good, just saying that I don't understand how it knows what values it should be getting from cold-ish valves.
It is a bit of a ground-breaking product - first fully-automated valve tester for consumer use ever?
And it isn't that expensive either.

stratlover1964
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Re: VT1000: Can I Trust the Results?

Post by stratlover1964 » Sun Dec 08, 2013 9:22 pm

I'm of the same skeptical opinion - hence my retesting. Pre-amp valves are tested from cold within a minute. This is not long enough to make the glass envelope of the bulb hot - in most cases it's barely even warm. I'm retesting for my own peace of mind, knowing that cold valves behave very differently to warm valves. And the manual states that the only 'problem' with this is that there is 'nothing to gain'. I've found that immediately retesting the valve (up to 5 times) results in a little variation before the results settle.

The purpose of the unit is to 'grade' output valves within a collection and to help you find dual triodes with matching values. This isn't an AVO or Amplitrex so it doesn't need to worry about providing meaningful data outside of an individual's collection.

stratlover1964
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Re: VT1000: Can I Trust the Results?

Post by stratlover1964 » Sat Dec 14, 2013 6:23 am

Further to my previous post, here's an interesting thought that suggests that each unit needs time to 'acclimatise'.

Interesting.

http://www.sweetwater.com/insync/orange ... climation/" onclick="window.open(this.href);return false;

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