In my experience, tube dampers are the least effective of all tweaks I have tried.
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Like Dopogue, I use silicone O-rings, but I purchased them online where I could be sure I got a formulation that would take the heat. They're available very cheaply and in my experience work as well as the Herbie's, the only others I've tried.
What effect they have is, like most things audio, dependent on the situation. I find they make more difference on octal tubes than 9-pin miniatures, and that they make more difference in units that have top mounted tubes rather than the tubes enclosed within the chassis. In some instances, they've made no discernible difference at all, but I still use them because it makes me feel better.
Okay, no kidding. The black o-rings at the hardware store (take a tube along to get the right size) have never melted on me. Ever. But I use them only on small tubes such as 12AX7s and 6922s and should have said not to try them on power output tubes like El34s, 6550s, KT88s or anything else that runs really hot. My mistake.
'black' may be OK for low power tubes. Black may be Viton, Buna 'n' and many others, including just plain rubber.(neoprene?)
Silicon (red?) has silicon oil in it which can migrate out and make a real mess, on higher powered tubes. If i had tubes and thought damping would help, and it may in certain feedback situations, I'd use EP, which will take more heat, is inert to many (certainly around the house) chemicals and is not too soft. EP stands for Ethylene Propolene.
If all you care about is maximum hi-temp use, try Kalrez. Good luck finding this at the local emporium, but I think that 500f should be good enough for most power tubes, too.
I just bought some EAT tube dampers, and still making an assessment of their effect. I do notice a difference. They make the presentation more firm and solid in the lower registers. It is probably dependent upon the type of tube you have, and how microphonic it is. I was skeptical because the 6H30 does not seem to be microphonic, but the dampers are still doing something. I was worried it would make the sound dead or soften the treble, but this is not the case. EATs won't work on wide tubes, but it is definitely worth a try.
As to claims of prolonging tube life, well who can say?
I have no idea how hot a well-driven power tube can get. That's why I suggested the Kalrez. That'll take anything, short of a meltdown. For preamps, most anything should do.
The reason I specifically do NOT like Silicon is that they are made with a liquid binder which under some (admittedly VERY unusual) conditions can 'weep' out.
This binder is silicon OIL which will really mess something up. Without getting real toxic, I don't know how I'd remove it. I don't think soap and water will touch it.
TVAD, Do you mean f or c temp scale? Silicon is generally considered good to about 450f = 230c. That is about as hot as your home oven can get and not really all that hot. We used silicon on equipment flanges which were water cooled. This means temp no higher than in the 90s c. The equipment itself ran at 600c = 1110f and was used in semiconductor processing.
I think you tube guys are right. I don't see how a tube could run THAT hot!
If I ran tubes and was seriously interesting in damping microphonics, I'd use 2 different rings per tube.
I don't know specifically which compounding we used at work.
Here, however is a link to a site which shows 2 different silicon compounds with way different max temps listed.
I would say the higher temp one is to be preferred. At least for output tubes.
My experience with o-rings tells me I would tend to avoid the silicon. While I doubt in home use you'd ever get one to weep, there is a binder oil as part of the compound. We used to put them in an oven at over 100c+ at very low pressure. They would weep out oil. We couldn't use them as sold to us for reasons completely unrelated to tube guys use as a damper. Later, we found a source for pre-baked rings and began using them.
I stipulated that it would be Very unusual for this to actually happen. Fact is, Silicon O-rings have a silicon oil binder in them. Period. If you saw evidence of this on a preamp, it would probably be WAY too hot. Output tubes? I don't know how hot they get. You are more likely to see such oils on output tubes, but still and all, since I've never seen it noted, I'll have to call it a real long shot.
If I owned a tube amp......and felt the need for tube damping, I'd make sure I bought either Kalrez or Vacuum baked Silicon. Your gonna have to trust me on this one. We chased a contamination problem for months in a 'wafer fab'. A place making 'chips'. We knew everything but the cause. One engineer suggested the silicon O-rings as the cause. We baked some ourselves and collected a couple teaspoons of oil from the catch cup we fabricated. In all fairness, we baked maybe enough silicon rings for 100 tube dampers. But, when we used 'em, the problem went away like we flipped a switch.
In short, the oil is real, You will only see it if something is seriously wrong and WAY over heats. I may have OCD!
fantastic system!!! how did the EAT tube dampers work out? i use one on the 7308 tube i put in my Zanden DAC...stunningly good results. The Zanden normally takes a JAN phillips which is surprisingly musical given its cost relative to more expensive tubes. But it is super-microphonic. you can snap your fingers 5 feet away and hear it come thru the speakers. but not with the EAT in place. And yes, the music improved as well...tighter bass, more solid voices, soundstage, et al.
eventually, i upgraded to the 7308 which still benefited in much the same way.
Because my CJ ACT 2 pre has 6h30p tubes (but cannot fit the EAT tube dampers due to the way they laid out the tubes), i have just ordered o-rings. curious if you have had any further observations on your 6h30p tubes...which i have heard are not too susceptible to microphonics.
thanks for any advice.