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


    Dirty Tube Sockets?!?!?!

    MechEngVic
    MechEngVic

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    Post by MechEngVic on Thu Sep 17, 2020 9:10 pm

    Yesterday, my amp (Dynaco ST-70 Series II) started crackling and popping during low volume listening, no red-plating or arcing tubes, no resistors burning, no speaker blowing boom of a capacitor failing, just crackles and pops and the high-low bias LED's flickering.

    (You set the bias of this amp by turning a trim pot until both LED's are of equal brightness, they also pulse in time with the music when it's loud. These LED's are sensitive to AC fluctuations and will go up and down in brightness. I say all this about these LED's so you'll understand why I mention them flickering with my issue)

    I instantly turned off the amp and did a quick look and sniff. No burning smell nor anything that looked wrong.

    I decided to pull the six tubes, I inspected the socket seats and saw what looked like a tiny bit of carbon deposit on a couple of them. I grabbed a thin wood dowel and some isopropyl alcohol and gave them all a good reaming. Then I retensioned the seats and slapped the tubes back in. I turned on the amp and it is running smooth so far, cross my fingers.

    This is the first time I was able to fix (hopefully) this type of crackling and popping with socket cleaning and retensioning. I had a very similar type of crackling and popping happen a different time and it turned out to be a bad driver tube. Anytime I remove and install a tube I re-tension, but never did much in the way of corrosion removal. These sockets are about 1.5 years old and this amp runs several hours a day.

    Is what I experienced typical of what happens when tube/tube socket contact is compromised?

    Also, what do you use to clean tube sockets?
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    mijohn

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    Post by mijohn on Fri Sep 18, 2020 12:12 am

    Apart from impaired contact of tube pins with the sockets, internal tube issues can cause crackling noises, from  expansion and contraction as tubes heat up to tiny pieces of metal breaking away from electrodes etc. Some people have reported more dramatic symptoms when pins intermittently loose contact with the socket.

    In your case cleaning and retensioning has done the trick.
    I use various  tobacco pipe cleaners dipped in isopropyl or Deoxit.


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    MechEngVic
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    Post by MechEngVic on Sat Sep 19, 2020 1:19 am

    Welp,

    My amp started crackling again.

    It was a power tube.

    The crackling was so subtle and steady I didn't think it could be a power tube, there was no arcing or red-plating... Until I turned off the lights. Then I could see the faintest of sparking coming from within the EL-34. It was just a steady non-escalating crackling sound and light sparking from the tube.

    It took a couple of days and several on and off cycles for the problem to go from occurring after several hours to occurring a few minutes into the warm-up cycle. That's why I was thinking my socket cleaning had fixed it. I'm glad I took the time to do the cleaning anyway, and I'm ordering some proper brushes for the job.

    The tube is replaced and I'll be watching the amp carefully for the next several cycles.

    The many ways a tube can fail surprise and confuse me! This was a new one to me and I've had tube amps for almost 30 years!
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    mijohn

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    Post by mijohn on Sat Sep 19, 2020 4:24 am

    The same thing happened to me a couple of months ago, a rustling noise in one channel. The EL34's had been running well for  over 7 years, but I took it as a signal that the tubes had had there day and replaced the complete set after cleaning the sockets with pipe cleaners and Deoxit.

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    Bob Latino
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    Post by Bob Latino on Sat Sep 19, 2020 8:48 am

    mijohn wrote:The EL34's had been running well for over 7 years

    This part of your post is not really a good idea .. 7+ years on a set of output tubes is too long unless this piece of gear was used very sparingly ..

    Consider these facts about tubes ..

    1. Vacuum tubes have a finite life .. Eventually all vacuum tubes will either have their filament burn out OR "short" between the cathode, screen(s) and plate OR lose their vacuum OR the sound of the amp/preamp will just slowly degrade over time.

    2. Output tubes should last about 3000 - 4000 hours and driver tubes maybe 5000 hours. If you go much over these times, the sound of your amp/preamp will start to degrade very gradually to a point where you might not even realize that the sound has degraded. Your amp/preamp may lose a little top end. The soundstage may collapse a little. Your music system may lose a little of its "jump factor" on musical peaks.

    3. As long as your amp/preamp is ON, the tubes are slowly wearing out. You don't have to be playing music through your system to cause tube wear. Shut the component OFF if you are not listening to the music. The only exception might be if you are taking a short break from listening (lunch break ?) and you know you will be back listening within 15 to 30 minutes or so.

    4. Keep spare tubes for your tube gear in your home. Keep at least one tube of every tube type in your amp/preamp. When you replace tubes that are still running OK but are old, keep them as spares to keep the music flowing in case you lose a tube during a listening session. Mark on the tube box the day that tube was removed from your music system.

    Bob

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    mijohn

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    Post by mijohn on Sat Sep 19, 2020 11:39 am

    I agree with you entirely Bob, all good and relevant points you make there.  
    I only use my tube gear when I sit in the hot seat and seriously listen to music. My music listening sessions are up to about 2 hours, 5 days a week, that's roughly 520 hrs a year multiplied by seven =  3640 hrs. I use a desktop silicon based system for background music the rest of the time.
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    Hops

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    Post by Hops on Sat Sep 19, 2020 5:32 pm

    Bob, what driver tubes do you recommend for the VTA-120? The sleeve of one of the ones that came with my kit said USA Made 5963 / 12AU7 ,and RCA. Which of the many iterations of RCA's are these? The Amp sounds great, and I would be happy to replace them with the exact same thing when these wear out. I already have a spare matched quad of Sovtek 6550's, and a spare rectifier.
    Bob Latino
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    Post by Bob Latino on Sat Sep 19, 2020 7:04 pm

    Hops wrote:Bob, what driver tubes do you recommend for the VTA-120?  The sleeve of one of the ones that came with my kit said USA Made 5963 / 12AU7 ,and RCA.  Which of the many iterations of RCA's are these?  The Amp sounds great, and I would be happy to replace them with the exact same thing when these wear out.   I already have a spare matched quad of Sovtek 6550's,  and a spare rectifier.

    Some of the best driver tubes for any of the VTA amps would be the USA made (RCA, GE, Sylvania) 5963, 5814 or 6189 tubes. These three tubes are military/industrial versions of a 12AU7 tube. They are getting in short supply but you can still find them on Ebay at fairly reasonable prices. 5963 tubes will command a lower pricing that the other two not because they are any "less good" but because the supply of these tubes is greater than the other two. Another great tube is the Mullard "Valve Electronic" CV4003 . These are also still available on Ebay but at somewhat higher pricing than the other three. Expect to pay $50 - $100 USD for each one of these ..

    Bob
    DavidR
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    Post by DavidR on Sun Sep 20, 2020 7:47 pm

    Here's a good guide to the various tube variants.
    http://www.vacuumtubes.com/12au7.html
    On the left-hand column is a purplish area with other tubes. Just click on a tube type and you will have a guide for all the variants available with that tube.

    There is another website that has descriptions for the various variants and manufactures types. Subjective of course. I'll see if I can locate it.

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