Shock mounting for tweed-style chassis configuration

[Luthierwnc]

Hi Guys,

I have a fun little amp that uses a 5879 as the overdrive tube in a 1X12 combo. It is mounted tweed-style with the chassis open to the back and the controls on top at the back. I'd like to protect that tube a little better against the slings and arrows of SPL and wanted to know if any of you have built/seen/considered an amp that gives some shock protection for the chassis. I've got some ideas but none proven.

Thanks, as always, Skip

PS RIP, Jim

[ampgeek]

I have seen the shock absorber put between the tube socket mount and the chassis on many occasions. Cut the basic outline shape from a sheet of silicone (~1/32"-1/16" thick), punch a whole through it large enough to slip the tube base through (either a dime or penny diameter IIRC) and screw it down.

Could be a bummer though if you are wired up already.

I have never seen a direct comparison between with and without but every application I have seen/heard about indicates "success".

I just built a small 10" combo with a 5879 in the preamp and used this technique for the first time. Haven't mounted in the cab yet but will report back once I have.

Cheers,
Dave O.

[Luthierwnc]

I was thinking of shock-mounting the whole chassis, sh

[10thTx]

I've slipped silicone strips between the chassis and wood cabinet. It seemed to be a minimal help.

What worked better (IMO) was what ampgeek mentioned. The silicone slipped/stretched over the socket base.

with respect, 10thtx

[tubeswell]

For small-signal pentodes in combo amps, I've used right-sized O-rings banded around the tube envelope, as well as mounted between the tube socket and the chassis (black O-ring barely visible on the EF86 socket in the attached pic). With the latter, I also use small nylon grommet/bushings in the socket screw holes (the little white things barely visible on the EF86 socket in the attached pic). Low-tech and it works fine.

[rogb]

^^^^^^^^^
almost exactly how I do it, especially with the lively EF86. I add a metal shield over the top of the o rings, aiming for a snug fit

Works well with 12AX7s tuned for gain too.

I slide O rings on all pre amp tubes and the PIs too.

I've needed to do this in all combos that are going to be cranked.

[LeftyStrat]

I'm kind of at a loss on how to do it in a tweed style combo. The way the old Ampeg VT-22 did it was interesting (google for pics).

I'm just throwing crazy ideas out there, but I might consider not mounting the chassis to the back plate, but have it suspended from the top of the combo, with long bolts going from the top, through the chassis to the bottom of the chassis, though some thick rubber washers, through some metal washers and finally nuts. Maybe a couple of nuts tightened against each other so the rubber isn't compressed. You have to use a back plated mounted to the chassis, and then maybe a rubber mat on the back plate to help it float.

Ampeg heads literally floated in the cab.

Another way would be springs or rubber or bungie cords mounted between the chassis and sides of the cab.

Just trying to think outside the beer, I mean box.

[wyatt]

For small-signal pentodes in combo amps, I've used right-sized O-rings banded around the tube envelope, as well as mounted between the tube socket and the chassis (black O-ring barely visible on the EF86 socket in the attached pic). With the latter, I also use small nylon grommet/bushings in the socket screw holes (the little white things barely visible on the EF86 socket in the attached pic). Low-tech and it works fine.

That's the way every tube socket was isolated on any '50's Fender I've owned. O-rings/gaskets between the socket and the chassis. Though then they went an extra step and added a braided ground from the socket the chassis.

[overtone]

I was thinking of shock-mounting the whole chassis, sh

On that kind of chassis I have used well nuts with an additional rubber washer from the plumber between the chassis top and the cab:

cs head bolt
cab
rubber washer
chassis
well nut
(I think I mount them the wrong way around? Like this: T)

best, tony

[Luthierwnc]

Thanks All,

I decided to mount the chassis in a new combo cab with the tubes down. I've replaced/vibration fitted the pentode tube socket with a homemade shock mount and I'm going to suspend the whole chassis like an Ampeg V-series with side mounts. A friend gave me a large sheet of 1/2" dense foam rubber (like you might use for foot mats). That will be the insulation between the side-mounted supports and a matching set above attached to the side of the chassis.

Now for a new problem. I'd like to do something like a Matchless or Vox front baffle but Mojo doesn't sell the T-Bar that separates the grille cloth and the tolex anymore. Anybody know where those can still be had?

Cheers, sh