Shock mounting tubes?

[Steve Conner]

Hi all,

As my Ninja Deluxe project lurches on, I'm now partway through building my first ever combo amp. I've already made my own chassis from 1/8" aluminium to fit the 5E3 cabinet, and mounted the transformers to it. Now it's time to cut the holes for the tube sockets.

My question is whether it's worth the extra hassle of rubber mounting the tubes. Does it help to cut down microphonics and suchlike? Would it help protect them against shocks? In my previous amp build, I made a sub-chassis for the tubes that was mounted on the rubber things you use for mounting reverb tanks. But that was extra work, took up more room in the chassis, and once all the wires were in place, it didn't really seem particularly springy. I see that no classic Fender or Marshall ever bothered with shock mounts, and they all work fine...

[dai h.]

I think it's generally considered a good thing esp. for a combo (since the tubes are typically near the spks.). If a shock-mounted subchassis for the tubes is too much work, how about rubber grommets or washers(IIRC Matchless did/does this)? Silicone rubber seems to hold up real well to the heat. I made some very crude washers cut from a sheet of silicone rubber a long time ago for the EL34 sockets on my Marshall combo and they didn't melt.

[Don Symes]

I see that no classic Fender or Marshall ever bothered with shock mounts, and they all work fine...

Mesa did a rubber mount thing on some of the Boogies (the entire chassis ... I think the called it SUS4), but they're the only ones I know of.

Unless you're building a gain monster or using a microphonics-prone tube like the EF86, I probably wouldn't bother unless a particular position showed itself to be a problem. Ted Weber sells a shockmount kit for 9-pin tubes that uses the standard screw locations -- hm, but you're not in North America.

Anyway, hope this helps!

[dai h.]

that's right, I think they hung the chassis down from the combo (top of it) by rubber washers or something like that. THD did the shock-mounting a sub-chassis the tubes were on already mentioned. Matchless the rubber grommets on the tube sockets. I've seen old shock-mounting tube sockets and mentions of shock mounting to reduce noise in the Radiotron book, so this must have been done for some time. Guess it depends on the gain also. If it isn't isn't that high, somewhat microphonic tubes seem okay to use.

[Steve Conner]

Well, as (bad) luck would have it I am using an EF86 as the first stage in my dirty channel, which has a good deal of gain I expect this amp to be carried around a good deal since it's a smallish combo, so I guess I should probably shock mount all the tubes. I'm using original Mullards, RCAs and Telefunkens, and I'd hate to think of my good tubes getting trashed prematurely.

[hasserl]

If you're using an EF86 I would attempt to shock mount it in some fashion. Otherwise you'll be constantly fighting with microphonic's. I would attempt to shock mount just the pentode socket if possible.

[Bruce / Mission Amps]

Well, as (bad) luck would have it I am using an EF86 as the first stage in my dirty channel, which has a good deal of gain I expect this amp to be carried around a good deal since it's a smallish combo, so I guess I should probably shock mount all the tubes. I'm using original Mullards, RCAs and Telefunkens, and I'd hate to think of my good tubes getting trashed prematurely.

Drill out the two mounting holes of the 9pin socket larger and install tiny rubber grommets.
Then use 4-40 x 3/4" long machine screws to hold the socket in the chassis.
Use long enough screws that you can put two nuts on the screw from the inside of the chassis so the two lock together and do not over tighten them to the chassis... that will squash the grommet too tight and not let the socket "float".

[bob p]

I like Bruce's idea of using rubber grommets. Maybe you could even use something like a rubber shoulder washer if you have those on-hand.

IIRC someone around here posted photos of his sandwiched construction method, where he mounted the tube sockets on pieces of G10/FR4 and passed the tubes through holes in the chassis. He put turrets on the G10, mounting them radially around the tube socket, so he could mount components between the socket and the turrets, and connect wires to the turrets. He used a rubber sandwich between the G10 and the chassis to damp vibration. I thought it was a pretty clever design, but I can't remember who to give credit to. I think its around here under a thread with a vague name, like "pics of my new amp design" or something like that.

I also vaguely remember reading something about shock mounting in the Radiotron manual. IIRC, the reason that the military needed ruggedized tubes with shock mounting was for things like aircraft operations. On those old prop-drive planes, the vibration in the airframe was pretty significant. Trucks, tanks, jeeps and ships also jostled and tossed tubes about, but in the aircraft it was like the tubes were mounted onto a vibrator that never stopped vibrating.

[bob p]

found it:

http://music-electronics-forum.com/s...ead.php?t=1949

[Enzo]

I'd do Bruces idea backwards. rather than drill out the socket holes, I'd drill out the chassis holes and mount grommets in them. Then pass the socket mount screws through the grommets.

Two nuts jammed does allow for you to leave slack and still be secure, but I prefer to use a nylok nut. It will stay put as well.

Run a ground drain wire from the socket frame down to the chassis. Especially if you are going to use a shield.

[mykey]

the whole shock mounting thing can be better understood by looking at the Ampeg V series (the real Ampegs, not crate Ampegs). here was an example of transformers, circuit boards, etc... on real industrial shock mounts, which made the amps more roadable. Does it suppress the microphonics? not a heck of a lot.
When you are dealing with a high gain circuit and the tubes tend to ring, introducing some negative feedback in the first preamp stage is more effective. After all it's the circuit that makes the tube microphonic, not really the tube's fault.
Connecting for example 7pf 1000V silver mica cap between control grid and plate will usually provide enough feedback to stop the ringing, without having to select a special preamp tube.
adding similar small amounts of negative feedback to other stages will be needed when gain of preamp is very high., to keep the oscillation under control.
Then again I have heard people say that plastic tube sockets are better because ceramic sockets caused microphonics, again that really did not prove to be true either.
then you can look back at the phono preamp designs which were the first to use the rubber tubing in the screw hole to make the socket "float" or the screw holes were padded with rubber grommets. Did this reduce the microphonics? only slightly, not really enough for a high gain guitar amp.
Shock mounting, good for the road, good for the preservation of the tubes, but not really amazing at reducing microphonic ringing.

[Steve Conner]

Hi guys,

Thanks for the many ideas. I like the system that Retrodyne used, with the tubes on a flexibly mounted subchassis sticking through holes in the main chassis. That was how I did it in my previous project, the Ninja Toaster.

I can see how shock mounting might not make that much of a difference to microphonics. After all, the sound waves will hit the tube directly as well as vibrating through the chassis.

However, I've been working on this amp for years, and it has already existed as a head for quite some time, with no shock mounting:

http://scopeboy.com/gallery/index.php?showimage=299

It's been gigged like this (although obviously in a cabinet ) with no problems. I suppose it just doesn't have a great deal of gain compared to a 5150 or Mess O'Booger, and that's why there hasn't been any trouble. So I guess I'm more thinking of the "roadability" as Mykey called it.

[mykey]

I can see how shock mounting might not make that much of a difference to microphonics. After all, the sound waves will hit the tube directly as well as vibrating through the chassis.

However, I've been working on this amp for years, and it has already existed as a head for quite some time, with no shock mounting:

you hit the nail right on the head, the sound from the speaker returns to
the surface of the tube. When this sound is in phase, the tube oscillates.
If the sound is out of phase, it cancels.
But don't be afraid to add another gain stage to get some grind, tunning the
amp for higher gain is trickier, and it seems like you are ready to tackle
the more advanced design phase. It's not impossible to balance higher gain
and reliability although some designers such as mesa have sacrificed reliability for gain.

[Enzo]

I sell a tube retainer for the PV C30. It clamps the tubes in so they don't rattle. I was discussing the tube vibration with a mechanical engineer who works in automotive. I was describing my retainer as something that prevented the tubes from vibrating. He pointed out that the tubes would always vibrate, but my thing was preventing them shaking around.

Ever hit a bump and the antenna on your car starts swinging wildly? The mechanicla system that the antenna and car form together are such that the antenna AMPLIFIES the vibration of the car.

In your amp, the vibration that is ambient is not what will get to your tube. It is the mechanical amplification by the chassis flexing to the vibration and so on. SHock mounting the tube will cut down on that action. And microphonics directly into the tube might not be affected, but the vibration picked up by the whole chassis will no longer be able to conduct into the tube.

[Steve Conner]

That's interesting, Enzo. I guess it stands to reason that the chassis would pick up more vibrations than the tubes themselves, because it's bigger, and in a combo amp, physically screwed to the cabinet too.

As regards building a "more advanced" amp, I submit that I already built it years ago!

http://www.scopeboy.com/toastpix.html

The Ninja Toaster was my take on the Dual Rectifier sound. It has up to 5 stages of gain before the PI, a parametric EQ (of my own hybrid tube/SS design) for extra-brutal mid scoopage and bass boostage, and it certainly does sound angry. I spent a lot of time playing with gain structure and coupling capacitor values, and I included another tone stack before the stages that distort, to give more control of the voicing.

This time round, I'm going for the "Less is more" approach. My new creation will still get pretty dirty, especially with humbuckers and the volume cranked enough to overdrive the power amp. I just stuck the EF86 onto the front of a regular clean channel, so it has about a factor of 50-100x more gain than a 5E3 or Twin. If I want more gain I can always stick a Metal Zone or two in front of it.