Tube spring retainers...how much is too much pressure? WXT wafer base vs taller tubes

[minim]

I'm about to sell this amp, a JCM900 that came stock with the wafer base WXTs. I've since fitted taller JJ 6L6s and the retainer tension is noticeably increased on these tubes. I have tried to find info on whether there are different lengths of retainer however most vendors seem to be selling a generic retainer ("fits 6L6, EL34, 5881", etc).

Just wondering what your thoughts/experience are/is on this. I have read reports of tubes cracking due to direct contact with retainers which is where my concern lies. I want to make everything's up to scratch before selling.

[Mick Bailey]

They sometimes have way more tension than I like. I gently pull upwards on the cap with the tube removed to 'excercise' and stretch the spring just a little. Don't overdo it otherwise it will be too slack and then you'll be removing coils.

[Justin Thomas]

I've actually lengthened the springs before. The material is not particularly elastic. It's stiff, andnot necessarily "easy" to reshape, but it can be done.

I'd use a small pair of needlenose pliers to get between a couple winds at one end of the spring, while holding the retainer end in either vise grips, clamp, vise, etc. and just pulling a bit. One the material is stretched, it holds its shape well.

I've also cut them to length & then used needlenoses to bend up the retainer end & reattach it.

Justin

[nevetslab]

Power & Rectifier Tube Hold-Down Clamps

While I prefer this style of tube clamp to the different shapes of Bear Trap clamps, which all too often don't hold the tube well, and allow the power tubes hanging upside down in Fender combo amps to flap about, and couple resonances from the speakers below them. After finding numerous 6550 power tubes in Ampeg SVT tube amps having failed from the spring/top-had mating flap digging into the tube glass, causing cracks, I've been adding hi temperature Silicon Rubber sleeving to the clamps to prevent that.



I went to McMaster-Carr, found two sizes of this sleeving (McMaster-Carr #3038K14 & #3038K122), available in 10ft lengths ($10.47/10ft & $9.63/10ft), and initially was just putting the 3/16" ID x 5/16" OD sleeves over the spring/tab joints. I've since added a grommet made of smaller tubing 3/32" ID x 7/32" OD, and having measured the ID of the top hat, calculated the circumference of the hole in the hat, and slit the tubing down the length, and having learned how to work it into the hat, it adds cushioning of the tube under the spring tension.



The 'wings' initially had been left as is, though I've since added the larger of the two sleeving sizes, cut short and slipped them onto the wings, which with KT-88 tubes and EL34 tube, the top hat now does a good job centering the tube with fully-cushioned hold-down clamps. On the 6L6 tubes, I'll usually do some bending of the spring tab of the 'hat' to bend that out then down, and so similar with the wing's tab, since the tubing adds some width to the tabs. After this shaping exercise, you end up with a nicely cushioned tube held firmly into place. I also bend them out for 6550's, which maybe is overkill, but when you have an amp as heavy as Ampeg SVT-CL's or Fender Super Bassman, there's a lot of vibration induced in transit, even with the amp in a well-built road case. I maintain the rental inventory of CenterStaging, LLC in Burbank, CA, and the tube failure from breakage has gone down significantly over the years from applying these measures.



The taller tubes, like EL34's, do indeed increase the applied hold-down force. I've tried pre-streching those springs with little success. I've yet to have one of the clamp assemblies let go and break a tube. And, granted, adding the fabricated grommet into the top hat hole increases the hold-down tension, but with the sleeving/cushioning, my tube breakage problems have stopped. On Fender Twins and other similar tubes hanging upside down, I'm no longer getting the vibration-induced noises that I had been getting.

[minim]

Ok so I went with your recommendations and used a couple of stretching methods and they have made the difference. I must admit that prior to my initial post I was somewhat sceptical about stretching them as the spring material is extremely hard but I guess everything bends once you exceed its elastic limit.

Nice rundown there Nevets. Might be superfluous for my situation but mandatory for hard gigging and touring amps I'd imagine.

[dugdiamond]

Oh Man I have had problems with those spring tensioner thingamajigs!
Marshall 1959 Superlead from very early seventies. It had a bad habit of killing 6550s.
I took me a several times to figure out why the tubes in this amp would suddenly go gassy? The spring would rub on the tube envelope just barely enough to wear a microscopic void into the glass and evacuate the vacuum. Only after killing numerous NOS 6550 tubes did I finally figure it out. Only one less expensive set of Chinese tubes offer up a visible clue to the naked eye. The others required a strong magnification lupe to view any damage and etching to the crystalline structure of the glass. All of it being noted at about the same place. Right where the spring met the clip.
I started out with an octal of near perfectly matched truly NOS Tung Sol 6550's . Now I only own three!
I use very high heat resistant, orange colored, fat O-rings. Basically a high heat cock ring around the tube with a smaller one on top of the tube too.