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RE: Tube Explosion????

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FenderLover

In Reply to: RE: Tube Explosion???? posted by timp on January 16, 2012 at 13:24:57

Ok, is that 9VAC or 9VDC? And is that measured with no tubes, at all, in the unit or just the 6DJ8 pulled? Plate voltage on the 6DJ8 is 90VDC per side, right? What are you reading across the cathodes?

I've heard of units that burn out tubes fast. But, to actually cause vacuum lost is kind of a new one for me. These are used/pulled tubes that went bad, correct? Could be just a co-winkee-dink that two lost vacuum and has nothing to do with the settings of the unit.

I'd get some relatively cheap Sovtek 6922 or something similar to do the voltage measurements. Until the issue(s) is resolved.
http://www.opentip.com/Musical-Instruments/Amplifier-Partstu (Open in New Window)

Follow Ups:

RE: Tube Explosion???? - timp 16:52:19 01/16/12 (13)
BTW

Yikes! i just measured b+ going to the plates. They are reading 230v with the load! Wow. How did that happen? I am not sure. My PSU b+ is 250v ish. After 10k plate load, it still is 230v. I am messed up here.

Any suggestion?

Thanks in advance.

Timp
- What preamp is this... - wheezer 16:10:34 01/18/12 (8)
  and if your Vp is the B+ and not lowered by the plate loading, check your heater supply.
  - RE: What preamp is this... - timp 18:57:04 01/18/12 (7)
    Hi
    
    All is well. The plate voltage reads well below 90v. What did not account for was that I needed the tube to settle to draw the current.
    
    I wonder why the tubes imploded. I will never know. I have been burning the tubes tho...
    
    Thanks all
    - RE: What preamp is this... - wheezer 19:05:45 01/18/12 (6)
      Use an NTC on the primary and secondary windings.
      0.02.
      - RE: What preamp is this... - timp 20:02:04 01/18/12 (5)
        
        In Reply to: RE: What preamp is this... posted by wheezer on January 18, 2012 at 19:05:45
        
        Hi Wheezer
        
        Are you referring to a thermistor just as this? http://www.legacydistribution.co.uk/downloads/NTC-thermistors/SCK.pdf
        
        If so, will give it a try.
        
        Timp
        
        RE: What preamp is this... - wheezer 14:28:34 01/20/12 (2)
        
        In Reply to: RE: What preamp is this... posted by timp on January 18, 2012 at 20:02:04
        
        They might be?
        The NTC should be listed as CL for current limiting.
        Note the attached indicates the R for the % of current loading.
        Hope this helps.
        
        Cheers,
        Wheeze
        NTC CL type (Open in New Window)
        
        RE: What preamp is this... - timp 16:59:47 01/20/12 (1)
        
        In Reply to: RE: What preamp is this... posted by wheezer on January 20, 2012 at 14:28:34
        
        Hey wheezer I will look for the NTC online. It sounds like an excellent plan.
        
        RE: What preamp is this... - wheezer 17:48:08 01/20/12 (0)
        
        In Reply to: RE: What preamp is this... posted by timp on January 20, 2012 at 16:59:47
        
        The heater can be tricky as there's usually not that much headroom to work with. Buy a few different sizes.
        They can generate a lot of heat. I've found the one that works best for that circuit, typically runs too hot. So I go down a bit in resistance.
        Cheers,
        Wheezer
        
        RE: What preamp is this... - Wojciech 23:10:38 01/19/12 (1)
        
        In Reply to: RE: What preamp is this... posted by timp on January 18, 2012 at 20:02:04
        
        I experienced implosion of kt90 regulator tube in old ARC d51 amp I was trying to check . After reforming PSU caps for a day Ive changed worn regulator tube and a minute later Kt90 imploded with loud puff of a short- fricking scary, to witness ;)
        
        RE: What preamp is this... - timp 17:00:46 01/20/12 (0)
        
        In Reply to: RE: What preamp is this... posted by Wojciech on January 19, 2012 at 23:10:38
        
        Mine made a loud thumping noise too. It was pretty scary for sure. It shouldn't happen. But it does! So if there is anyone out there who've experienced tube implosion let us know.
        
        Thanks for sharing.
- Recheck the entire PS rail - FenderLover 19:11:58 01/16/12 (3)
  Must be a wrong resistor(s) or wrong tap point or something that is causing that kinda voltage to pass through. I'm pretty sure 6DJ8/6922 should NOT be running much above 90-100 VDC onto each anode plate.
  
  Might as well check all tap points off the rail. Who knows what voltage you are putting onto your output tubes? Maybe only 90VDC?
  - RE: Recheck the entire PS rail - timp 19:43:02 01/16/12 (2)
    I think you're right!
    
    The resistor is 12k not 10k. So that should lower the B+, right? And what do you mean by tap point? I measured the voltage by putting Neg side of the voltage meter to the ground (chassis) and the Positive side of the voltage meter to the pin 1 and 6 (the plate) of the 6dj8. I did this with the tube in of course. As you've suggested I am using a sovtek tube in the mean time.
    
    Thanks
    - RE: Recheck the entire PS rail - FenderLover 20:36:14 01/16/12 (1)
      Most power supplies have several parallel pi-filter circuits and points where voltages are tapped off (see schematic---C,D,E points, where B = 480VDC going to CT of primary side of output transformer).
      These are the voltages to measure to be sure the PS rail is properly setup and working. Usually, B > C > D > E, as in this Ampeg amp. If you read E = or > C or D, then there is a problem.
      From there, you measure the voltage on the anode plates. If there is a discrepency, the problem(s) lies between the tap off the PS point and the anode. A good suspect would be a bad dropping resistor in that line or a bad coupling cap in the previous section.
      http://unofficialampeg.com/schematics/gv-22.gif (Open in New Window)
      Edits: 01/16/12
      - RE: Recheck the entire PS rail - timp 21:13:12 01/16/12 (0)
        
        In Reply to: RE: Recheck the entire PS rail posted by FenderLover on January 16, 2012 at 20:36:14
        
        Thanks for the homework.
        
        This will take a while for me to understand.
        
        Thanks a lot for your help.
RE: Tube Explosion???? - timp 16:47:52 01/16/12 (0)
Hi

Well. I've never experience tube implosion myself. It's a new experience for me for sure.

Fenderlover, thanks for following up with me. I think your advise is sound. I will not put any expansive tubes in until i get my measurement right. Something is not right. Or it may just have been a freak coincident.

Timp

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