Very low bias readings on 20th Shiva - UPDATE / explanation.

  • Thread starter Thread starter RockStarNick
  • Start date Start date
RockStarNick":1b5duj1h said:
Ok, so I just got off the phone with Bogner. Apparently, because of it's design, the Shiva has massive bias-drift depending on the volume of the amp.

If you bias it at idle, after warming up for 5 minutes, it'll read super low (like mine).

If you bias it running it cranked, it will read 10+ HIGHER on the meter.

The tech said that lots of guys (like me) don't know this, crank up the bias, and then blow up their amp when they go to crank it. Not good. I'm probably going to set mine back to factory specs and just play it.
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Biasing is for idle current zero signal only. All tubes current rises with signal level. Of course it will rise very high, that is 100% normal with signal level. On most tube amps running AB1 Push/Pull biasing no more than 70% plate dissipation at idle (zero signal) is safe. The old tale of biasing amps beyond that were guys trying to get power tube break up at much lower volumes. But most modern amps get the distortion and breakup from the preamp. So you actually want the power tubes a little colder around 60-65%

Bogner just fed you that "bias drift" line to keep you from biasing your amp to hot. Because many bozos out there bias their amps way too hot.
 
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