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    Testing 7199 valves/tubes

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    hansfob

    Posts : 21
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    Age : 53
    Location : Rickmansworth, England

    Testing 7199 valves/tubes

    Post by hansfob on Thu Oct 26, 2017 9:02 am

    Hi, I have about 7 spare 7199s for my ST70. If I were to test use them in my ST70 and one happened to have a fault for whatever reason am I likely to damage anything expensive in my amp? I do not have the means to test them on a tester so my easiest option is to just try them whence my question.
    Thanks for any help anyone may provide.

    Big Harry

    Posts : 15
    Join date : 2016-06-19

    Re: Testing 7199 valves/tubes

    Post by Big Harry on Thu Oct 26, 2017 9:22 am

    If the tubes are not gassy or have a short, then plugging them into your amp won't be a problem. My theory on this is with used tubes, I always test them before using them. I don't believe that a 7199 with a short or gas will do serious damage the amp, but why take a chance.
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    hansfob

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    Re: Testing 7199 valves/tubes

    Post by hansfob on Thu Oct 26, 2017 10:04 am

    Thanks Harry,

    I do not think they are used as they are all in their original boxes. I know that does not mean they haven't been used which is why I wanted to test them somehow. I think I'll have to find/pay somebody with a tester. It sounds like I only need very basic tests to ensure safety of my amplifier and let my ears do the rest of the testing?



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    Peter W.

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    Location : Melrose Park, PA

    Re: Testing 7199 valves/tubes

    Post by Peter W. on Thu Oct 26, 2017 10:14 am

    hansfob wrote:Hi, I have about 7 spare 7199s for my ST70. If I were to test use them in my ST70 and one happened to have a fault for whatever reason am I likely to damage anything expensive in my amp? I do not have the means to test them on a tester so my easiest option is to just try them whence my question.
    Thanks for any help anyone may provide.

    Look for someone with an AVO tester - they are "real" testers by any measure.

    Sadly, you are "over there" such that offering my Hickok 539B is not practical.

    Big Harry

    Posts : 15
    Join date : 2016-06-19

    Re: Testing 7199 valves/tubes

    Post by Big Harry on Thu Oct 26, 2017 2:50 pm

    GE tubes don't have the best lettering on them at least mine don't. If the lettering on your GE tubes looks new and isn't smeared, missing or otherwise compromised, then there is a good chance they are NOS tubes. The mil spec tubes should have a green or blueish green lettering on them if they are original to the boxes and probably labeled either Sylvania or Philips. If you don't have access to a reliable tube tester, then plug one tube into your amp at a time and listen for strange noises such as a hum or a howl coming from the channel that has the tube under test. or a blueish glow inside the tube which means the tube is gassy.
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    Peter W.

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    Re: Testing 7199 valves/tubes

    Post by Peter W. on Thu Oct 26, 2017 3:05 pm

    Big Harry wrote:GE tubes don't have the best lettering on them at least mine don't. If the lettering on your GE tubes looks new and isn't smeared, missing or otherwise compromised, then there is a good chance they are NOS tubes. The mil spec tubes should have a green or blueish green lettering on them if they are original to the boxes and probably labeled either Sylvania or Philips. If you don't have access to a reliable tube tester, then plug one tube into your amp at a time and listen for strange noises such as a hum or a howl coming from the channel that has the tube under test. or a blueish glow inside the tube which means the tube is gassy.

    OK - there is blueish glow and there is blueish glow.

    A clear blueish glow around the glass surface of the tube has much to do with fluorescent inclusions in the glass - glass that has some radioactive salts in it or other materials - not at all uncommon.

    A  milky blueish glow that fills the entire envelope is indicative of small amounts of gas. Keep in mind that if these are truly NOS tubes, and have had only the getter flashed and no other testing beyond that, a bit of gas might well remain and will be absorbed by the getter flash in short order.

    Point being: DO NOT throw away an otherwise faultless tube for a bit of milky glow - give it a couple of hours anyway and see if the condition clears up - and if not, but the filament still works, I would be glad to take them off your hands for postage and packaging.... Twisted Evil

    Big Harry

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    Re: Testing 7199 valves/tubes

    Post by Big Harry on Thu Oct 26, 2017 5:13 pm

    What I meant by blueish glow is not on the glass but inside of the plate structure. I have equipment that use 7199's and probably have 10 new and good used tubes in my stock and since the 7199 is a small signal tube I've not at this point seen any type of fluorescence or blue/purple glow in one unless it is really gassy. I've seen plenty of output tubes do it though. Since the 7199's are getting scarce and rather pricey, I won't discard one unless it's beyond using reliably
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    PeterCapo

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    Re: Testing 7199 valves/tubes

    Post by PeterCapo on Fri Oct 27, 2017 8:28 am

    The thing about 7199s… even if you have tube tester, what do the results mean?  I have a considerable supply of 7199.  I put them all in my tube tester – and all of them without exception test shorted.  This seemed very strange, because I knew most of them were [supposedly] NOS, and I used some of them in my Stereo 70 with no problems whatsoever.

    A brief search over in the tubes asylum at Audio Asylum revealed that others had found the same thing.  I also found the following discussion that I recommend reading, and note post #29 in particular: http://audiokarma.org/forums/index.php?threads/75-of-all-7199-i-find-are-shorted-whats-up.497345/

    Seems to be some kind of idiosyncrasy with the 7199 that reminds me Dynaco did not list voltage test points on all 7199 pins – perhaps related.
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    Peter W.

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    Re: Testing 7199 valves/tubes

    Post by Peter W. on Fri Oct 27, 2017 8:51 am

    This might be related to the type of tester. My Hickok has several notes on which pins will read as "shorted" for the 7199.

    In general, they are fairly rugged tubes - but they are also many times quite microphonic. Those few failures I have experienced have been for that reason other than shorts.
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    Peter W.

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    Re: Testing 7199 valves/tubes

    Post by Peter W. on Fri Oct 27, 2017 8:56 am

    Big Harry wrote:What I meant by blueish glow is not on the glass but inside of the plate structure. I have equipment that use 7199's and probably have 10 new and good used tubes in my stock and since the 7199 is a small signal tube I've not at this point seen any type of fluorescence or blue/purple glow in one unless it is really gassy. I've seen plenty of output tubes do it though. Since the 7199's are getting scarce and rather pricey, I won't discard one unless it's beyond using reliably

    Blue on the plate structure would be the same mechanism as blue on the glass. Agreed on not trashing an operating 7199.
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    PeterCapo

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    Re: Testing 7199 valves/tubes

    Post by PeterCapo on Fri Oct 27, 2017 9:09 am

    I have B&K and Hickok and both read the shorts. Don't recall if the guy in the posting mentioned what kind of tester he had.
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    hansfob

    Posts : 21
    Join date : 2010-10-24
    Age : 53
    Location : Rickmansworth, England

    Re: Testing 7199 valves/tubes

    Post by hansfob on Fri Oct 27, 2017 9:09 am

    Many thanks for the information everyone. Based upon the article that PeterCapo posted, the comments about lettering that Harry posted and the experience that Peter W has had with respect to showing shorts but also seemed to be OK when used I think I will just suck it and see by trying one or two of them.

    You may be wondering why not wait until one of the ones I am actually using fails before trying another: Well, I was wondering if I really needed a big stash especially as some time ago I purchased a VTA board for the ST70 that I have yet to use. If I considered selling on some of my 7199s knowing whether they work or not would be essential which is why I was asking.

    Thanks so much again.
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    peterh

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    Re: Testing 7199 valves/tubes

    Post by peterh on Fri Oct 27, 2017 11:25 am

    PeterCapo wrote:The thing about 7199s… even if you have tube tester, what do the results mean?  I have a considerable supply of 7199.  I put them all in my tube tester – and all of them without exception test shorted.  This seemed very strange, because I knew most of them were [supposedly] NOS, and I used some of them in my Stereo 70 with no problems whatsoever.

    A brief search over in the tubes asylum at Audio Asylum revealed that others had found the same thing.  I also found the following discussion that I recommend reading, and note post #29 in particular: http://audiokarma.org/forums/index.php?threads/75-of-all-7199-i-find-are-shorted-whats-up.497345/

    Seems to be some kind of idiosyncrasy with the 7199 that reminds me Dynaco did not list voltage test points on all 7199 pins – perhaps related.
    Send them to me and i'll dispose them :-)

    As i am in a possesion of a uTracer and have already made a connector plug for
    7199 i can comare the tube curves ( and suggested working points ) whith the manual.

    Forget "simple tubetesters" they will fool you.
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    Peter W.

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    Re: Testing 7199 valves/tubes

    Post by Peter W. on Fri Oct 27, 2017 12:36 pm

    PeterCapo wrote:I have B&K and Hickok and both read the shorts.  Don't recall if the guy in the posting mentioned what kind of tester he had.

    If you have a "red-box"Hickok, it will be more prone to reading extraneous shorts. Read the notes section of the manual carefully.
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    PeterCapo

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    Re: Testing 7199 valves/tubes

    Post by PeterCapo on Fri Oct 27, 2017 4:22 pm

    Will do.

    Big Harry

    Posts : 15
    Join date : 2016-06-19

    Re: Testing 7199 valves/tubes

    Post by Big Harry on Fri Oct 27, 2017 6:22 pm

    I use my B&K 747 for testing small signal tubes as I believe it is better at finding shorts and gas than either my Hickok 539B or 600A. I've only found one shorted 7199 on the B&K and when it was installed in one of my ST70's, it hummed like crazy. I replaced the original driver board shortly after that with a VTA board which I'm really happy with.

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