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    bad tubes or bad tech ?

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    scottlowe

    Posts : 38
    Join date : 2014-04-05

    bad tubes or bad tech ?

    Post by scottlowe on Mon Sep 08, 2014 12:44 pm

    so i was just wondering what is the problem with my experience with this amp .I have had it now for almost three years and it has never worked for more than 60 days between "VISITS" to the shop .and some of those visit have been 12 months apart[$]  so this time i was using it into heresy speakers at a very low volume . . so I can't afford this and am going to get it repaired and then I won't even feel right about selling it.I am so bummed out .I have never been able to just enjoy it for long .I am just saying that my[50 plus year old] st-70's that i sold to afford thiswere rock solid reliable, I WISH I HAD EM BACK...

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: bad tubes or bad tech ?

    Post by Bob Latino on Mon Sep 08, 2014 12:52 pm

    Hi,

    Four quick questions ..

    What amp is this ? How old is it? Who built it ? Have you checked your line voltage ?

    Bob

    scottlowe

    Posts : 38
    Join date : 2014-04-05

    Re: bad tubes or bad tech ?

    Post by scottlowe on Mon Sep 08, 2014 2:42 pm

    Hi , Bob It is a VTA ST-120 .And I need to say that My tech seemed a bit perplexed by the soft start circuit and that was the problem last time and he also mentioned that it "cascaded" other parts.I have been looking at the line voltage and it has been between 118.7 and 119.4 depending on day and time but I have been watching it for over two years .My amp went down in 2012 and stayed down 14 months then i got it fixed [I thought] but I also wonder about a bad pre tube i put in before this happened and it made a bit of hum on the right channel so i changed it and a friend came over and i turned it quite low ,[so low it took a minute to even notice it was off] and i took all the tubes out and put a set [when it went down i had three cleartops and a set of kt 120,s from j mcshane and a webber copper cap to run the kt-120,s i put some 6550,s in and a tube rectifier and got the bias up to .520 and popped a fuse .I also need to say that the fuse I was using was only a 3 amp not a 5 amp but on the other hand that three amp ran fine for over two months,with the kt-120's I don't know enough to even ask the right questions, I just want to hear my music.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: bad tubes or bad tech ?

    Post by Bob Latino on Mon Sep 08, 2014 4:10 pm

    Try a new rectifier tube in the amp .. It could be a bad rectifier ?

    If you are going to have the amp worked on by a tech, I would suggest sending it in to one of the two authorized VTA amp techs. If you send me a PM through the forum, I can give you the Email address of our two techs ..

    Bob

    scottlowe

    Posts : 38
    Join date : 2014-04-05

    Re: bad tubes or bad tech ?

    Post by scottlowe on Wed Sep 10, 2014 8:48 pm

    Hi Bob thanx for your response I don't know what' PM through the forum" is refuring to but I don't care about security HERE is my email scottlowe58@yahoo.com . I am ready to send it to someone that can make it right as I have repeated so many times I just want to enjoy my tunes. not the speakers not the amp just the music. And believe it or not I am dumb enough to still hope it can happen.SCOTT

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: bad tubes or bad tech ?

    Post by Bob Latino on Wed Sep 10, 2014 8:55 pm

    Hi Scott,

    I have Emailed you directly about sending your amp in for service by one of our authorized VTA amp technicians ..

    Bob

    msupr

    Posts : 11
    Join date : 2012-11-21

    Re: bad tubes or bad tech ?

    Post by msupr on Tue Sep 16, 2014 1:02 pm

    I can vouch for Bob's technical support, great results, fair pricing.

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: bad tubes or bad tech ?

    Post by deepee99 on Tue Sep 16, 2014 1:07 pm

    msupr wrote:I can vouch for Bob's technical support, great results, fair pricing.
    "Fair pricing"? I'll say. Bob has never charged me a nickel to answer one of my many thousands of dumb questions.
    Bob, I hope Troy Madden was on that list you sent. Nothing of mine has ever left Troy's hands without vast improvements. Not to diss any others in that circuit with whom I have not dealt, but I'll swear by Troy, for sure.

    jimmytamp

    Posts : 8
    Join date : 2013-06-24

    Re: bad tubes or bad tech ?

    Post by jimmytamp on Fri Sep 19, 2014 1:27 am

    Bob's technical support is a top notch...

    msupr

    Posts : 11
    Join date : 2012-11-21

    Re: bad tubes or bad tech ?

    Post by msupr on Fri Sep 19, 2014 9:45 am

    My comment was in reference to the technicians Bob recommends to look at a unit that is giving you trouble, it was in no way, shape or form to imply that Bob charges, for all the help he gives to all of us. Bob is a saint to deal with all of my stupid questions he has fielded over the years.

    scottlowe

    Posts : 38
    Join date : 2014-04-05

    Re: bad tubes or bad tech ?

    Post by scottlowe on Tue Dec 09, 2014 2:15 pm

    ONE simple question Why does my st-70 [1962] unmodified run flawlessly in the exact same conditions as my st-120 and yet all the voltage questions. IF voltage is the issue then why does my OLD st-70 not fail????????????? thx Scott

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: bad tubes or bad tech ?

    Post by Bob Latino on Tue Dec 09, 2014 2:58 pm

    scottlowe wrote:ONE simple question Why does my st-70 [1962] unmodified run flawlessly in the exact same conditions as my st-120 and yet all the voltage questions.  IF voltage is the issue then why does my OLD st-70 not fail????????????? thx Scott

    Hi Scott,

    The VTA ST-120 run about a 70 volt higher B+ than a stock ST-70 ... As such, the ST-120 is a little harder on the parts and also less tolerant of a bad solder joint or any other minor build issues. This is especially true of solder connections to the B+ high voltage system which include the quad cap, SCM, ESL, Russian PIO caps, power caps on the driver board. Sometimes after many heat/cool cycles a solder connection may go "partial" .. This can happen to even an experienced DIY builder who has built a number of DIY tube amps or preamps.

    I am not implying that you personally "did not build the amp properly" but bad solder connections do happen in kit built amps. Once or twice a year I get an Email from a customer with virtually the same symptoms that you list above. It runs OK for a period of time and then starts blowing fuses. This is why I suggested that you send the amp in to one of our VTA amp technicians to go over the amp and check it out ..

    Bob

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: bad tubes or bad tech ?

    Post by sKiZo on Wed Dec 10, 2014 4:09 pm

    Tech support has already been spoken for, but let me throw in that the ST120 is a well designed amp and has been trouble free for me ... only problems, I caused myself with custom tweaks, and I don't hold anyone but me accountable for that.

    If you want to try it yourself ...

    Under normal circumstances, the usual suspects are cold solder or missed connections. First plan of attack is to drag out the magnifying glass and inspect each joint closely - the solder should be shiny and flowed evenly over the metal without blobs or bridges. Give each wire a little wiggle with an insulated tool to make sure it's solid. A real important note - use the original build sheet to check off each item as you confirm it's right - Method trumps just poking around inside.

    I'd also look REAL close at any excessively long "tails" on capacitors and such that could be shorting on the case. Fairly common around the edges of the VTA board, and any problem could be intermittent as you're experiencing. Wouldn't be a bad idea to snip those to get rid of any excess as you work your way through the checklist. Same thing with the sockets and multicap as you're talking fairly tight quarters there also. I clip mine just proud of the solder.

    Pay close attention to the "S" steps in the directions which denote points that are soldered right away. Easy to forget later on and leave you with an intermittent connection. The build ain't done until you finish it, AND go back through the checklist at least one more time.

    I know it can be frustrating when problems develop, but ... the ST120 is an EXCELLENT daily driver, so once you figure out what's wrong, it's well worth the effort.

    Maintarget

    Posts : 209
    Join date : 2013-02-10

    Re: bad tubes or bad tech ?

    Post by Maintarget on Wed Dec 10, 2014 11:23 pm

    Well said sKiZo,
    I built my ST-120 about a year ago and have almost 700 hour on it with only one self inflicted issue Shocked
    Otherwise I have enjoyed mine everyday.
    Good luck Scott I hope you are jamming soon.

    ArlanB

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

    Re: bad tubes or bad tech ?

    Post by ArlanB on Thu Dec 11, 2014 1:28 am

    Scott,
    You will thoroughly enjoy the ST-120 when all is right.  I have one of Bob's very first VTA ST-120 kits to go out his door.  I purchased it in June of 2008.  It is an all original issue, no upgrades with high gain VTA board.  It worked from the very first smoke test and as of this date the only failures have been the tubes.  Sounds so good with my setup I just can't say enough.  

    ArlanB

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