The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Mk III's: jiggle a tube, get static

    Share

    veloceracing

    Posts : 7
    Join date : 2013-10-12

    Mk III's: jiggle a tube, get static

    Post by veloceracing on Fri Oct 18, 2013 6:18 pm

    Why is it that the newbies always have the ridiculous questions????

    Something curious is happening with/to my beloved Mk. III's: after six months of great enjoyment one of the Svetlana Winged C 6550's decided to go nukuler.  Or, at least I think it did: I flipped on the amps and with the preamp volume at 0, I heard white noise emanating from one of the speakers which kept getting louder by the second.  I flipped off the amps and decided that one tube was bad.

    As I was taking said tube out via a rocking motion, I could hear static coming through the corresponding speaker as I jiggled the tube.  I chalked it up to a cap that hadn't discharged or something equally benign.  Again, the preamp was off, the source component was off and (yea, before anyone asks) the damn amps were off!  But (hint...) they were plugged in.

    I inserted the original, tired KT88's that came with the amp and everything was fine: re-biased the amps, even turned them down to 1.3V and rocked out to the groovy sounds of Slim Whitman.

    Not wanting to leave good enough alone, I decided to have the amps converted to triode.  So I started removing the tubes and (come on, you know the rest), when I got to the socket that had held the "bad" tube, I got the same staticky sound as I jiggled the KT88 to dislodge it.  Again, being quite adept at ignoring reality, I just blanked it out.

    So the amps get converted to triode, we fire them up, get glorious sound out of them and I left for home.  Having received a replacement set for the suspect 6550's I proceeded to remove the KT88's.  Yup, same staticky sound on that one tube socket.

    So ... what gives?  The preamp has not been on for weeks now.  The amps have not been turned on for weeks since the triode mod.  Yet every time I jiggle a tube in that one particular socket in order to remove it, I get crinkly, static (apologies for the high-fuluting, hyper-technical nomenclature) noise.  Never when I insert a tube, just removing it and always the same socket.

    Any help/suggestions will be greatly appreciated.

    sKiZo

    Posts : 1313
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Mk III's: jiggle a tube, get static

    Post by sKiZo on Fri Oct 18, 2013 7:04 pm

    I'd suspect the "static" has nothing to do with the tube implosion you referenced, but is simply an old socket with a weak connection on one or more of the pins. The noise you're hearing is more than likely discharge from the filter caps as the pins make and break contact while you're wiggling or removing the tube. Putting a tube in may not do it as you're applying pressure and working with another set of forces.

    Long as you have a techie type handy, I'd suggest having that socket replaced.

    Easiest way to tell if the Winged C is really bad would be to shuffle the tube into another socket and see if the problem follows. Once again, probably unrelated to your "static" issue.

    veloceracing

    Posts : 7
    Join date : 2013-10-12

    Re: Mk III's: jiggle a tube, get static

    Post by veloceracing on Fri Oct 18, 2013 8:28 pm

    Howdy!

    Thank you so very much for that quick and reasonable-sounding response. My tech (yea, as if it needed mentioning that I don't do my own work....) re-tensioned the sockets when I first bought the amps but we've already agreed to change all four sockets.

    Thank you, also, for the tip on checking the tube. I'll do that, just to make sure that it did indeed go bad. And yes, I'm certain that any possible failure of that tube may not be related to the "static."

    Thanks again!

    veloceracing

    Posts : 7
    Join date : 2013-10-12

    Re: Mk III's: jiggle a tube, get static

    Post by veloceracing on Fri Oct 18, 2013 10:03 pm

    UPDATE:
    Fully realizing that the majority of you folks have been abusing the "refresh" button so as to read the next installment of the mystery static, here is an update:

    I installed a new quad of Penta Labs Shuguang KT88's, biased the amps to a conservative 1.0V and ... glorious sound emanated forth from the speakers!  I might just become a convert to the KT88's.  The triode conversion sure lends a fuller dimension to the sound.  But with two new variables (tubes and conversion) it may be difficult to determine which made the most difference.

    If all goes well, the next step is to insert the imposing Philips 5R4GYS in place of the humble (yet oh so reliable and ridiculously inexpensive) Chinese 5AR4's.


    ArlanB

    Posts : 52
    Join date : 2011-01-23
    Age : 69
    Location : Santa Cruz, California

    Re: Mk III's: jiggle a tube, get static

    Post by ArlanB on Sat Oct 19, 2013 12:38 am

    I think that you may discover that the Penta Labs KT88SC MQS is a satisfying tube.  I have been using them in my VTA ST-120 now for over 3 years and have been extremely satisfied with their performance.  Their failure rate seems to be lower than Gold Lion, J/J, Elektroharmonics etc.  The Tube Store is now marketing an in house brand "Preferred Series KT88".  In their add they pointedly mention that their new tube is also known as Penta KT88SC.  They liked the Shuguang KT88 solid plate tube enough to but their name on it.  Good luck with your socket change.

    ArlanB

    veloceracing

    Posts : 7
    Join date : 2013-10-12

    Re: Mk III's: jiggle a tube, get static

    Post by veloceracing on Sat Oct 19, 2013 12:47 am

    Thank you very much for the endorsement. When I had a pair of Quicksilver Mid-Monos, I was able to experiment with most common power tubes and I, too, was happy with the Penta Labs KT88SC MQS as well as their 6L6 product.

    But ... to go off on a tangent, you are the Nth person to comment unfavorably on the reliability of the Gold Lion KT88's. The J/J and EH's don't need to be mentioned; we all have horror stories about them. But I take it that the QC of the Gold Lion KT88's is still unsatisfactory? I have a matched quad of them and, honestly, am just not comfortable plugging them in. Their KT77's, on the other hand, are fantastic.

    Jim McShane

    Posts : 154
    Join date : 2011-10-19
    Location : South Suburban Chicago

    Re: Mk III's: jiggle a tube, get static

    Post by Jim McShane on Mon Oct 21, 2013 9:29 pm

    veloceracing wrote:Thank you very much for the endorsement.  When I had a pair of Quicksilver Mid-Monos, I was able to experiment with most common power tubes and I, too, was happy with the Penta Labs KT88SC MQS as well as their 6L6 product.

    But ... to go off on a tangent, you are the Nth person to comment unfavorably on the reliability of the Gold Lion KT88's.  The J/J and EH's don't need to be mentioned; we all have horror stories about them.  But I take it that the QC of the Gold Lion KT88's is still unsatisfactory?  I have a matched quad of them and, honestly, am just not comfortable plugging them in.  Their KT77's, on the other hand, are fantastic.
    The quality of the KT-88 Genalex is VERY good. I am having a failure rate of about 1/2 of 1% (down from about 1% previously) - most of which I catch before the tubes go out since I run them at 465 volts in the matching process. There are many 1000s of them in use right now working away quite happily. They are so reliable that I offer an extended coverage on them that goes beyond the factory warranty.

    The KT-88 Genalex sells in VERY large numbers, so more failures in total will occur. As well, the KT-88 IN GENERAL is a harder tube to make than most other power tubes, and the number of failures of any brand will be higher than the KT-66 or KT-77.

    Many of the failures in the early days of the Genalex were related to very poor quality of the "factory" or "distributor" matching. Sometimes the difference was large enough to cause one tube in a quad to be badly overstressed and fail. I strongly suggest these tubes only be purchased from vendors who match their own tubes at real operating voltages, and only do that following a proper burn in.

    There are a few other causal factors, but the bottom line is there is no reason not to use the Genalex you have if they were properly matched. In fact, if you didn't get them from me then I'll be happy to check the match on them for you at no charge if you'll just pay shipping both ways. Drop me a note if you want to take me up on this.

    Sponsored content

    Re: Mk III's: jiggle a tube, get static

    Post by Sponsored content Today at 2:01 am


      Current date/time is Sun Dec 11, 2016 2:01 am