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From: eacj@tcgould.tn.cornell.edu (Julian Vrieslander)
Subject: Re: Tube Warmup
Date: 23 Mar 90 15:46:53 GMT

I have a Counterpoint SA-3000, a recent hybrid tube/solid state design. The
Counterpoint folks claim that most of the wear and tear on tubes comes from
thermal cycling, as was pointed out in Jeremy Grodberg's posting.  I think
that the expansion and contraction of metal elements in the tubes cause
coatings on these surfaces to loosen and flake off, and that affects operating
efficiency.

Their solution (in their recent product line) is to leave the heater circuits
on (or at partial current) when the user shuts down.  There is no "power"
switch on my SA-3000.  There is a switch called "operate", and when it is off
the heaters are still active, you can see the tubes glowing.  The high voltage,
and other supplies, are turned off with the operate switch.  There is also a
"mute" switch, which simply causes the output relay to drop out, without
turning off any supply.   Counterpoint claims that this scheme substantailly
improves tube life.
-- 
Julian Vrieslander 
Neurobiology & Behavior, W250 Mudd Hall, Cornell University, Ithaca NY 14853    
UUCP: {cmcl2,decvax,rochester,uw-beaver}!cornell!batcomputer!eacj
INTERNET: eacj@tcgould.tn.cornell.edu     BITNET: eacj@CRNLTHRY

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From: rouellet@clitus.cs.uiuc.edu (Roland Ouellette)
Subject: Re: Tube Warmup
Date: Fri, 23 Mar 90 19:33:11 GMT

Julian Vrieslander writes:

>[... M]ost of the wear and tear on tubes comes from thermal cycling.
>I think that the expansion and contraction of metal elements in the
>tubes cause coatings on these surfaces to loosen and flake off [...]

It's not the coatings that flake off; it is the very tungsten that
makes the filiment which evaporates more quickly under thermal stress.

>[... L]eave the heater circuits on (or at partial current) when the
>user shuts down.  Counterpoint claims that this scheme substantailly
>improves tube life.

Old Sony Trinatrons (the kind with more than one tube) did this.  It
also gave them the instant on feature.  Other TVs would put a hefty
choke after the heater filament power supply so the filiments would
come up slowly & not blow themselves to pieces.

Lighting people who know what they are doing will use varacs or
rheostats in preference to breakers to make bulbs last longer.

These examples lead me to believe that such conventional wisdom has
been long verified.  [Doubtless Edison or Westinghouse did some
performance study in the late 1800's...]

R.
--
= Roland G. Ouellette			ouellette@tarkin.enet.dec.com	=
=	rgog1070@uxa.cso.uiuc.edu	rouellet@babym.cs.uiuc.edu	=
=   "You rescued me; I didn't want to be saved."			=