Shock mount tube sockets? Yet another thing I didn't know...

Timbresmith1

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Makes sense (and I suspect Rob may know that). Does it spec a certain method, say grommets, washers, rubber-mounted sockets? or does it just suggest shock isolation?
Packing up to move, so can’t find the book to confirm. Pretty sure the early AC-30’s had a shock mount stand-off for the ef… been a while tho
 

King Fan

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This is great stuff (or trivial details I never knew; same thing). Thanks to all.

Can anyone enlighten me why Fender had explicit grounds on the isolated output sockets? I'm not sure that metal-shell tubes would be a reason, and they must have been already on the way out in the tweed era. The pins that need grounding (including 1 for metal shells) were grounded on the lug side of things. Was it just the potential high voltage floating a mm from the grounded chassis? Arcing? What?
 

AlfaNovember

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Adding: another source for isolating washer material is down at the auto supply - Look for solid silicone vacuum hose, the colorful stuff sold to dress up an engine. 0.25" ID or so. Buy yourself a foot, and slice off washer-sized rings with a razor blade.

You can also source larger sized hi-temp silicone o-rings from old automotive headlight bulbs, they make dandy 'tube damping' rings, which allegedly help stop glass from ringing, and assuredly make you look serious.
 

dougsta

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I used 5 x EF80 valves in my EF80 pp amp head, 2 for the pre amp, 1 for PI and 2 for the pp output stage. I used McMurdo skirted sockets £4 each from here:

Didn't notice any microphonic issues, ran them at full volume put quite a few recordings put up on soundcloud.

Doug
Just checked my EF80 amp, I used the McMurdo skirted sockets on the 2 preamp EF80 valves and regular McMurdo sockets on the PI and OP valves.
The 2 skirted sockets were pulls from old reel to reel recorders that used EF86 valves, I did think about using those EF86's for a preamp but went with the EF80 as they can be had for peanuts and I liked the idea of a build with only a single type of valve.
I also added a switch to the 2nd EF80 stage for triode/pentode mode, I'd read about using pentodes for preamps @ valve wizards site and the idea he had about driving a high gain pentode from a triode stage.
Some clips here:
 

D'tar

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This is great stuff (or trivial details I never knew; same thing). Thanks to all.

Can anyone enlighten me why Fender had explicit grounds on the isolated output sockets? I'm not sure that metal-shell tubes would be a reason, and they must have been already on the way out in the tweed era. The pins that need grounding (including 1 for metal shells) were grounded on the lug side of things. Was it just the potential high voltage floating a mm from the grounded chassis? Arcing? What?
I would "guess"....

All that potential needs a return path in the event of an emergency! An isolated piece of metal housing hundreds of volts. Your seat cushion may be used as a floatation device!
 

Wyatt

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This is great stuff (or trivial details I never knew; same thing). Thanks to all.

Can anyone enlighten me why Fender had explicit grounds on the isolated output sockets? I'm not sure that metal-shell tubes would be a reason, and they must have been already on the way out in the tweed era. The pins that need grounding (including 1 for metal shells) were grounded on the lug side of things. Was it just the potential high voltage floating a mm from the grounded chassis? Arcing? What?

I assumed it was, in part, to ground the tube shield. We are talking about an era only 15-20 years after the birth of the electric guitar and they were still figuring it all out. Maybe it was a holdover from Leo's radio days?

And, for added thread reference, here are some additional examples from my former 1960 Fender Deluxe.
z960m0z.jpg

xDSohtn.jpg


I duplicated this when I built my clone, mostly for sh*ts and giggles.
0LHt70T.jpeg


This is spec’d in the Mullard amp book for the ef86

That makes sense for a pentode prone to microphonics. Thinking about it, every preamp pentode I've experienced — EF86, 5879, 6SJ7, 6J7, etc. — has been prone to noise and microphonics and the Fender tweed era did start with pentode preamp tubes.
 
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mountainhick

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Something related i came across the other day is with metal shell tubes, some have a pin that only attaches to the shell. That pin on the socket can be grounded to chassis as a shield to reduce or eliminate noise since it is not connected to any functional aspect of the tube.
 

Stevo Bambino

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I think the flexible ground strap is for shielding RF and EM noise while still isolating the socket from vibration. I used regular tube sockets mounted to some 1/8 inch thick rubber, then mounted the rubber to the chassis for a 6sj7. I have not finished building it yet so IDK how well it works.
 

rickmccl

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First time I saw shock mounting was in this recent video, psionic repairing a Matchless. Looks like o-rings
I failed to copy the timestamp, look at 1:30 for a few seconds.
 

FenderLover

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I've read in a few places that Gibson was the first to shock mount the sockets in 1948 on the GA-50. When I rebuilt mine, the rubber was shot and decided not to worry about replacing them. I'm not surprised at all that it still works fine. My Mesa has a shock mounted chassis, but not sockets. The socket grounding has to be to make the function of the 'shield' an electrical reality.
 

King Fan

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As a follow-up, I got in my ¼" grommets from TubeDepot. They're nice. Now I just gotta drill out the mounting holes to ¼" (that'll be easy) *and* find some longer #4 screws -- maybe 3/8" long I'm thinking.
 

chas.wahl

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McMaster has the red ones, silicone, slightly smaller durometer, somewhat more money ($9+ for 25 of the ones for 1/4" hole), much higher heat tolerance than styrene-butadiene (500 deg rather than 170).

Does nobody make a "fixture" plate (commercially) for grommet-mounting tube sockets?
 




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