From bw@ashbysolutions.com Fri Sep 20 13:07:07 2013
Subject:Replacing Tubes/Valves

Hi All,

My $0.02USD on the tube replacement issue ...

________
The Burn isn't the first piece of gear where the tube is not considered
a replaceable item. The user manual for every ART tube preamp I've
owned has said the same thing: don't replace the tube(s), it voids the
warranty. There's actually a reason for this, and it isn't, "so we can
charge huge markups on tubes."

Most modern gear with tubes (a.k.a. valves) -- especially items that are
90%+ digital -- use what is called a 'starved plate' design. Rather than
running at several hundred volts, as the tube was designed for, the
circuit runs at anywhere from 5V to 40V. At this low voltage, the tube
performs differently, and things like warmth and distortion may be a
little unpredictable. Many manufacturers work with tube suppliers to
make and/or hand-grade tubes that will work as required in their
starved-plate circuits; these tubes may have special properties not seen
in off-the-shelf tubes. When one replaces this hand-picked tube with
another -- including NOS varieties known for superior performance -- the
results may be different than expected. In some cases, the new sound
may be what the customer is looking for; but at the minimum, things like
'0-10' overdrive calibration may no longer be valid.

Some customers can understand and work around this issue, but I would
argue that the general population of musicians cannot. Given that tubes
in starved-plate circuits generally last 10x as long as normal (10-20
years), it's a perfectly valid *business* strategy to say, "Look, the
tube is not a replaceable part in this product. In the unlikely event
that it wears out, you'll need an authorized replacement." Now, this
strategy flies in the face of common wisdom that tubes last a couple of
years, and need customer replacement, but that doesn't necessarily make
the premise wrong. And yes, the tube will probably need eventual
replacement, but so did the battery in my DX7 RAM cartridge -- which was
soldered to the PC board.

________
An analogy is my Nissan Altima Hybrid: Its headlights are very hard to
replace; one has to practically remove the fenders to get at the bulbs
-- a situation I found bothersome when trying to upgrade the headlights
to high-lumen models from an aftermarket source. Nissan's take? They
feel that the bulbs they've chosen, properly mounted in a sealed case,
should easily last five years or more. Thus, they no longer consider
headlamps to be a user-replaceable part, and feel no need to make them
easy to access. As a DIY automotive guy, I find that situation
unfortunate, but given that most car warranties are at least three years
these days, I have to assume that the Nissan has done the math to show
that they won't be receiving a huge lot of warranty claims for burnt-out
headlights.

--
Regards,

-BW

Bruce Wahler
Ashby Solutions.com^(TM)
bw@ashbysolutions.com
http://music.ashbysolutions.com
877.55.ASHBY (877.552.7429)