[Vintage-Audio] More info on Scott LK-72 biasing

[Bob]

Carefull here..

Let's assume that the amp was designed correctly and with
Scott I would think it was. Dorking with the bias will
change the output impedance, the linearity and a few other
things. 

Power tubes fail for a few differtnt reasons. Drawing
current before the cathode is up to temperature is one
problem which tends to rip cathode material off the cathode
and spred it around the insides. The second is plate
temperature. If the amp is properly designed, the life of
the tubes should be several thousand hours like 10,000. In
class A configuration, the plate dissapation will be the
same whenever the amp is on whether or not you are listening
to anything. If class B or AB, then the dissapation will
depend upon how loud you are listening.

Divide the cost of the tubes by 10,000 to see how much it
costs/hour. $100/10,000 equals $0.10/hr. Also 10,000 hrs
divided by 4 hours/day 5 days a week=1000hrs/yr or a life of
10 years.

WBob

WBob


Roy Morgan wrote:
> 
> At 07:55 PM 7/13/2002 +0000, you wrote:
> >QUESTION:  Considering the high cost of 7591's, should I bias them slightly
> >"cool" for long life?
> 
> YES Absolutely no question YES.
> NO one needs the maximum amount of power that amp will deliver.
> NO one needs to pay curent prices for output tubes.
> 
> Bias them down to 80 percent of normal plate current and rest knowing you
> did the right thing.
> 
> Roy
> 
> Roy Morgan
> K1LKY since 1959
> 7130 Panorama Drive, Derwood MD 20855
> 301-330-8828 home .... 301-975-3254 work
> roy.morgan@nist.gov
> 
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