Shock mounting tubes

[Ptron]

Anybody got some good advice on doing this? This is the best plan I've come up with so far.

Those Marshall-ish brown plastic octal sockets might work ok this way as they appear to have pretty heavy duty brackets, however most of the noval sockets I've seen (or bought) have pretty flimsy mounting brackets.

It could also be done with springs.

Probably more springy (pardon the pun) than using rubber grommit but it starts to become quite a contraption. Plus the problem with flimsy mounting brackets still exists.

...And one last idea I had for shockmounting tubes that use those mounting rings that "clamp" the tube to the chassis.

The o-rings could be like the high-temp silicon rubber rings Weber sells as tube vibration dampeners. https://taweber.powweb.com/store/tubesktord.htm Kind of a cool idea I think, but probably hard to make work practically. It would be difficult to make sure the socket was completely floating and not rubbing on the chassis or mounting ring.

This is were I sneak in my "what do you think is the best socket, and where do you get it? line. Like I alluded to, I've bought a couple different kinds each of octal and noval sockets and have been dissapointed in how flimsy they were.

[pdf64]

My 1957 Gibson GA20 and 1972 WEM Dominator used the rubber grommit method, Gibson for all, WEM just for the 2 preamp tubes.
Ampeg used to float the whole chassis in a suspension system within the cab. I can't remember exactly how it was done, but it was very classey. Worth further research if you want to get into this.
However, I'm not sure that any of these methods have a tangible benefit, high gain combos seem to resist the feedback modes that this would suppress just with the regular construction methods, in my experience. Also difficult to see any benefit in how this would help protect the tubes from vibration; certainly with combos most of the vibration would be air bourne, as I see it.
Maybe try Angela instruments or Lord Valve for some high spec NOS sockets? Peter.

[jrfrond]

Ampeg used separate metal side panels UNDER the amp chassis side. There were rubber bushings between the tops of the side panels and the chassis, and the side panels were hard-anchored into the cabinet with bolts on the cabinet sides. Great system!

The only reservation I have about shock-mounting tubes using rubber grommets is that the heat will probably cause the neoprene to petrify eventually, and possibly fall apart thereafter. Other than that, no issues here.

[Enzo]

And make sure to run a ground wire from the main chassis to any metal subchassis you might use. Even if it is merely the socket mount ring.

The first way - rubber grommets - was often used. But you really only need one grommet. Grommet the chassis hole, then a bolt through the socket plate. Sorta like a reverb pan mount.

And consider that usually only the first tube is really sensitive to vibration, I wouldn;t think shock mounting the power tubes would have any benefit.

[Ptron]

And make sure to run a ground wire from the main chassis to any metal subchassis you might use. Even if it is merely the socket mount ring.

The first way - rubber grommets - was often used. But you really only need one grommet. Grommet the chassis hole, then a bolt through the socket plate. Sorta like a reverb pan mount.

I thought the dual grommet thing might be a little springier.

And consider that usually only the first tube is really sensitive to vibration, I wouldn;t think shock mounting the power tubes would have any benefit.

Oh. I guess I was under the impression that besides microphonic issues, shock mounting all the tubes in a combo was beneficial for reducing mechanical stress on their innards. Maybe that benefit was overstated?

In this particular case, it's not going to be a crazy high gain amp.

[Johnrcurry]

I'm working on a conversion of an old reel to reel tape recorder. It used the rubber grommet method on two of the eight tubes. Here are some pics of how they did it.

http://jrc.x10hosting.com/shock_mount/index.html

By the way, the grommets are still pliable after all these years. And there was a ground wire from the plate to which the tube sockets are mounted and the chassis.

[Enzo]

The goal is not springiness, the goal is to insulate the tube socket from chassis vibration. Nothing wrong with two grommets, just in my opinion not necessary.

The common problem in guitar amps, in particular combo amps, is microphonic tubes picking up chassis vibration. Far less of an issue in heads than in combos. But in general after the first stage, amps are not too terribly sensitive to that.

Check out the grommets on a reverb pan, those white squishy ones. They are soft pliable grommets. They are designed to prevent vibration from transmitting through them. Not that you likely see them, but the gromets that mount turntable motors are also soft and pliable. The typical hard rubber grommet is not used as a cushion, but rather as a bumper to protect wires from the sharp edges of chassis holes. Those are not designed with shock absorption in mind. You would do well, I think, to seek out some softer grommets for this project.

[Steve Conner]

I'm a big believer in this method. I've built two amps that had all the tubes on a subchassis, fixed to the main chassis by reverb pan mounts. The little rubber cylinders with threaded metal stalks on the ends: if they have an official industry name, I don't know it.

Whatever they're called, it seems to work great, I've never had trouble with microphonics. And I figured it would make the amps more roadworthy too. The only downside is that it's a hassle, it makes the construction more complex. It also feels a bit worrying when you go to pull out a tube, and the chassis squidges around.

I also mounted the eyelet boards and components on the subchassis to add weight.

[Ptron]

Heh, I think the squidginess will bug me too but it's one thing or the other I suppose.

I wasn't real big on the sub-chassis idea at first but I'm kind of warming up to it. I think the extra complexity would be offset by the fact that you only need to have shock mounting hardware on the one unit instead of individual tubes.

Steve, do you think the extra weight you added is critical to the sub-chassis holding it's own while everything around it jiggles? By my current layout, my sub-chassis wouldn't have much on it other than the tubes and a smattering of small parts. I'm also using some very stiff solid-core teflon hookup wire. I'm sure that doesn't help.

And make sure to run a ground wire from the main chassis to any metal subchassis you might use. Even if it is merely the socket mount ring.

Is this purely a safety thing? Not that it's difficult to do but I'm curious as to why it would be necessary if, say, I used epoxy board for the sub-chassis and the sockets only used mounting rings, no tube shields or anything.

[defaced]

I think if you could come up with some simple way to lock the sub chassis in place you could get rid of the sponginess while installing/removing tubes. Maybe two set screws that thread into the sub chassis and lock it to the main chassis.

[tedmich]

Morgan Jones makes amazing setups with "trapeze" isolation of preamp tube boards. Incredible attention to detail and clean design.....

IMO dampening is more important than elasticity though; a nice visoelastic urethane pad (sorbothane is a tradename) will absorb any short wavelength "microphonic" vibration much better.

McmasterCarr (who else?) has this stuff here:
http://www.mcmaster.com/#8514k112/=1acu8i

[Enzo]

The grounding of the sub chassis and stuff is not about safety so much, it is about potential noise.

[MarshallPlexi]

Doesn't Brian at Top Hat do his the way the first pic shows? His build quality always seems top notch.

[Chuck H]

Enzo said:

I wouldn;t think shock mounting the power tubes would have any benefit. .

I procured a box of about 25 old school Sovtek EL84's in matched pairs. In the high plate voltage amp I was using them in a pair would last a couple of months. Using a simple cork grommet and a different retainer doubled my tube life. But in fairness these tubes are notorious for mechanical noise. The difference may not be as profound with other tube types. Or even other brands of EL84's.

Chuck

[Enzo]

I make a tube retainer for the PV Classic 30. I make it to prevent tube rattle, but most guys claim it also extends tube life. The whole chassis vibrates and the tubes shake around. Ever hit a bump in the road and watch your radio antenna gyrate wildly? Those tubes can shake more than th chassis itself because they are sticking out. Clamping them in stops this. The chassis vibration is still there vibrating the tubes, but they no longer shake around. It was the shaking that killed them, not the chassis vibration itself. My thinking is that a good retainer to hold the tube obviates the shock mount.