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Vacuum Tubes for Amps
RTV Tube Damping
David deForrest (buybeac--(at)--uybeach.com) wrote:
: New High Performance Vacuum Tube Dampers From 3M
: Vibration Control Help Improve Musical Clarity and Focus
sniff... sniff... do I smell snake oil? Someone said "musical clarity and
focus"...
...
: ...The vacuum tube dampers resemble clear O-rings and are made
: of 3M ISD 110 Viscoelastic Damping Polymer,
...
OK. $4.00 each for a super-whoop-de-doo O-ring? That melts onto your tube?
A workable and highly effective alternative that I've used for quite some
time is the high temperature RTV gasket material sold in auto parts stores.
This gook goes for about $4.00 a tube (of gook, not vacuum...) and one
tube will treat MANY vacuum tubes. It cures to a dense silicon rubber...
: The 3M tube dampers, which have damping performance up to 140 C
: (284F),
... and the gasket material is good to 450F. By the way, vacuum tubes are
specified for dissipating their rated power at a glass envelope
temperature of about 200-250C, according to the data books. What does 3M
O-ring material do at over 200C? Does it decompose, melt, or just quit
damping?
Of course, it's preamp tubes that really need vibration damping, and they
usually aren't run that high, but I'd be careful about putting the rings
on high temperature output tubes until I knew it would not melt down into
the tube socket, glueing the tube in, or decompose in place.
...
: Application of 3M tube dampers is easy. Simply stretch the dampers to
: fit the appropriate tube, slide the damper over the tube and turn on
: the equipment. The heat from the tube will cause the damper to adhere
: to the tube, providing a permanent fit. Two dampers are suggested for
: larger tubes; one or two can be used for the smaller size tubes.
Application of red RTV gasket material is easy. You unscrew the top, and
apply a bead of gook all around the tube. Of course, there is a curing
time, so you can't just plug it in and turn it on.
I prefer one at the base and one near the top to leave most of the middle
area open for heat dissipation - both o-rings and rtv will prevent heat
>from coming out of the glass right under them. In most cases, a thinnish
bead will silence microphonic preamp tubes. You can adjust the amount of
damping by adjusting the amount of gook, and if you need more, you still
have the tube of gook. You have to use a razor blade to get it off, though.
For hard cases, you can use the RTV material as a glue to attach a heavy
metal ring to the tube. This adds decoupled mass to the tube which
requires that vibrational energy shake both the tube and the decoupled
metal ring, passing through the elastic material two times at resonance.
You can effectively move the resonance below audio this way.
In fact if you REALLY want to damp a tube, you can also use the RTV
material to glue the tube sockets into the chassis rather than hard
mounting them. This is a lot of work to do well, but now you have the tube
and socket soft mounted to the chassis, so you get a dissipative path from
the chassis, too. The chassis is MUCH more effective than the tube at
coupling in airborne sound to the tube, so this helps kill the vibration
on the way in. And of course, the chassis is the only path in to the tube
for structure-born vibration.
Rubbermounted tube sockets used to be available, but I don't know of any
source of them now. I suppose one could make a rubber mounted socket with
heavy rubber sheet, a socket and some patience, but that would be a labor
of love.
: This is the most effective, yet inexpensive, tube damper on the
: market. It combines damping performance that is equal to or better
: than many other styles of typical tube dampers, with a high-tech,
: one-size-fits-all design that is a first in the marketplace.
And of course, RTV is also one size fits all ;-)
I do respect 3M's research, and it is entirely possible that their special
viscolastic megapolymer is better per unit volume at absorbing vibration,
but a tube of auto gasket rtv offers you a whole lot more volume.
By the way, how did you test for effectiveness of all those tube dampers?
What metric did you use, and how did you run the tests? I'd like to see
the test data to see how much more effective these things are than the
other dampers on the market. I might just switch over to 3M O-rings
entirely if the data supports it. Would it be possible for you to post
the test data here?
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