Shiva + Power Brake = Blown Output tubes

Discussion in 'Amps and Cabs' started by ibeagle, Jun 30, 2006.


  1. ibeagle

    ibeagle Member

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    Bogners website says attenuaters are ok with the Shiva. So I hooked up my power brake correctly triple checked. 80 watt Shiva clean channel volume 12 o'clock. Master volume 12 o'clock. Power brake minimum attenuation. Turned on the amp and it sounded freakin awesome. Became a different amp, notes just bloomed, I was amazed, lots of touch sensitive overdrive, everything I've wanted in an amp. After 1 minute I blow an output tube. I had a spare pair of SED's bought as a matched quad, put em in and turn on the amp. Again after 1 minute, another blown tube. The power brake was on minimum attenuation, amp volume settings on moderate. This should not be stressing the tubes too much I would have thought. Some time later, new set of tubes, and I borrow a Hot Plate. This time I play for about 10 minutes without blowing a tube, but I turned the amp off cos I was scared of blowing another tube and I didn't have any spare. So what was going on here? Are power brakes harder on tubes than a Hot Plate? Everything was definitely hooked up correctly. I would love to run the clean Shiva through a hot plate for just a little bit of overdrive, but I need to be confident I'm not gonna keep blowing tubes.
     
  2. matte

    matte Senior Member

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    weird. i've been using a hotplate with a variety of amps (vht pittbull 45, vht deliverance, 3 bogner uberschalls, bruno 6l6 super 100, bruno ug 45, egnater mod 100, egnater mica tol 100, trainwreck express, thd flexi,etc.) without incident. i wonder if it's an impedence issue?

    one thing is clear. attenuation quickly reveals any weak links, as the amp is running at critical mass. i'm astounded to hear the difference in noise floors between different amps which are pushed to the same limits.
     
  3. Sniper-V

    Sniper-V Member

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    I used to have the PowerBrake and never had any problems and I actually bought it used a while back. I did recently sell it to a buddy and picked up a couple Hotplates and again, no problems....
     
  4. drbob1

    drbob1 Silver Supporting Member

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    Isn't there a potential problem with the Powerbrake and burning out some of the wiring? Maybe you just got a bad one?
     
  5. bobgoblin

    bobgoblin Supporting Member

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    i had the same thing happen w/a weber minimass & my '60 ampeg. new jj 6v6s & definitely hooked up correctly. i had been using it in that manner for close to a year, tho, so...as nothing else went up in smoke, i just chalked it up to having bought a tube w/an unusually short lifespan. btw, i still use the minimass & the ampeg, have been for a year, no problems.
     
  6. trainwrecker

    trainwrecker Member

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    I've had 2 transformers go with the Powerbrake, with the unit hooked up properly. Eerily similar to your experience, it would sound fine for a time then the fuse(s) blew, and the transformer with it. I like the powerbrake as it seems to capture part of the marshall tone that the others don't, but I won't use one again.
     
  7. benttop

    benttop Member

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    Have you checked the bias on your power tubes? If the bias is way off, running them at full power doesn't really help. I see a lot of people point fingers at attenuators when they haven't made sure their amp is properly tuned. Check your bias.
     
  8. John Phillips

    John Phillips Member

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    Probably just defective tubes. If the Shiva puts out even close to the claimed 80W, it's going to be really hard on the tubes when it's cranked - that's beyond the capability of EL34s which only just meet the spec, like many new-production tubes.

    I doubt the Powerbrake alone had much to do with it, unless it's actually faulty - especially since you were running it on only mild attenuation. It's one of the attenuators which most closely matches the impedance curve of a real speaker, which is why I use it as my load of choice for proof-testing amps.

    I've thrashed hundreds of amps through mine - every knob dimed, for a minimum of five minutes, and I have blown a few tubes, but not many really - and more 'brand new' new-production than tested old-production, FWIW. And just one OT, on a Marshall DSL50, which I think says more about the quality of the transformer than the Powerbrake...


    Regardless of what any attenuator maker says, I do think they are harder on the tubes than a real speaker though - I've seen good visible evidence of it on the bench. There's also the probability that you are more likely to crank the amp harder and more continuously through one than through a speaker.
     
  9. datguytim

    datguytim Supporting Member

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    Man - I will never use an attenuator! Never have, never will. Why not just get a lower wattage amp & crank the f*ck out of it? All it takes is an impedance reading mismatch and . . . POOOOOFFF!!!!!!! Bye bye tranny! Not about to take that chance with a '69 Superlead - NO WAY! This is why lotsa builders make 18 watters & the like. If you can't run an amp at it's optimal volume (whether 5 watts or 200 watts) - make the logical adjustment. Get an appropriate amp & save yourself the heartache!
     
  10. reaiken

    reaiken Member

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    Of course you realize, John, that this conclusively, beyond a shadow of a doubt, proves my theory that a purely resistive load is far safer than a reactive load. :D

    All kidding aside, the Power Brake can sure make an amp oscillate in a minute if it is prone to it, and I've seen it cause power tube redplating in high-voltage amps, where they were fine into a resistive load. The large impedance rise at the resonant point and at higher frequencies can also cause internal arcing in high-voltage amps, such as those trying to get 80W out of a pair of EL34s. ;)

    In my not-so-humble opinion, the PB needs a limiting resistor across the series inductor to tame some of that rising high-frequency impedance curve. It'll sound less buzzy, too. They also need to use a larger bipolar electrolytic cap (better yet, a film cap), because that little one doesn't look capable of handling the AC current of a 100W amp full-bore.

    Randall Aiken
     
  11. reaiken

    reaiken Member

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    I'm doing my best to stir the pot!!! :) I think everyone is argued out over the never-ending "clones" thread...

    John Phillips is probably asleep, or gigging, or he'd come back on me...

    Randall Aiken
     
  12. Rusty G.

    Rusty G. Member

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    Sounds to me like the same kind of problem with crossing the Sonic Discombob-u-lator with the Flux Capacitor. I did it once. . .Never again. :MMM

    Randall. . .I'm glad you came along and sorted it all out for us.









    It's really a shame that I don't know enough about electronics to be even able to hold an intelligent conversation with the man, much less add something to the conversation.

    My contribution. . .I'm using a Dr. Z AirBrake with a Voxer, an 18 watt amp to bring the levels down to less than window shattering. Works for me. Rock on!
     
  13. devbro

    devbro Member

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    I used a Hotplate with my Shiva and never had a problem. I ended up selling the Hotplate because I didn't like the attenuated sound. As already stated, the Shiva is known to be hard on power tubes. It runs about 515 plate volts. :eek: I've heard it said many times that only Winged C SED's can handle the load.
     
  14. ibeagle

    ibeagle Member

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    I've only used winged c tubes. One tube may have been defective, but two in a row is suspicious. My power brake worked fine through my marshall. I had the amp sitting out of the cabinet in a darkened room, and although both amp volumes were on about half and I was amazed at how much the tubes lit up when notes were played hard. There's always the overdrive pedal option I suppose. I have tried calling Bogner on another matter, but I live in New Zealand and the phone line was terrible, like I was calling mars, and they've already stated attenuators are fine.
     

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