Who makes this fitted grommet for tube hold-down clamp opening?

[Audiotexan]

You can get 'em here:
Spring Tube Retainer for 6550/ KT88, nickel finish - Accessories

Nice! I'd like them even more though if they'd only add the same material to the "wings" (inside contact points that touch the glass)

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[Enzo]

scratches on the glass are not cracks. If the glass was actually cracked, the tube would shatter.


And these are vacuum tubes, not projector lamps. They are not as hot as some apparently think they are.

[Leo_Gnardo]

Nice! I'd like them even more though if they'd only add the same material to the "wings" (inside contact points that touch the glass)

I'll be giving it a go with that copper Permatex. And heat shrink on the springs.

[Leo_Gnardo]

scratches on the glass are not cracks. If the glass was actually cracked, the tube would shatter.

I'd like to show ya but doesn't show up too well on photo. When you get a chance to scan some output tubes in a "modern" SVT, take a careful look at the 6550 domes, maybe you'll see some in person. I thought 'why doesn't it shatter,' but they don't. Usually.

And these are vacuum tubes, not projector lamps. They are not as hot as some apparently think they are.

True 'nuff and maybe that's the source of some of the "handle with cotton gloves, fingerprints are going to ruin your tube" malarkey.

[Audiotexan]

And these are vacuum tubes, not projector lamps. They are not as hot as some apparently think they are.

Well true to an extent..was just thinking that if the rubber windshield tubing is soft enough (some parts houses sell the cheapest crap they can find if it isnt required to meet a certain level ie: fuel line), then it'll melt/stick to the tube. Some folks get pissy about that. Some don't. *shrugs* Not like I was thinking they'd turn into a molten pile of rubber draped all down the sides of the tube or anything... lol

[jbltwin1]

You can get the fuel hose in small stuff too. It will hold up to the heat. I have used the GOOD ws hose for such uses and it held up but REAL long term, who knows. Tubes don't last TOO long now anyway so they come back more often! Mike.

[nevetslab]

And these are vacuum tubes, not projector lamps. They are not as hot as some apparently think they are.

Typical surface temp of the 6550 tubes in fan-cooled Ampeg SVT-CL is around 180 deg C. Probably less in the older SVT's having the 120mm fans.

[nevetslab]

Windshield washer tubing, maybe 3 or 5/32, split longwise and long enough to butt together without coming out. Maybe a little trim cement for stability till it dries? Made a lot of hole protectors that way. Mike.

I like that approach. There is high temp silicon rubber tubing that's probably suitable ID for the application. Once the length is determined to fit the ID, and it's slit with a simple jig for consistent slitting, that sounds like a winner! I'll give that a spin. Gotta get other hardware from McMaster-Carr anyway.

[guitician]

Red Silicone resists heat to 450 degrees 1 1/2" diameter washers here...

Better link...http://www.mcmaster.com/#99604a131/=u2ghp5

[nevetslab]

Nice! I'd like them even more though if they'd only add the same material to the "wings" (inside contact points that touch the glass)
[ATTACH=CONFIG]30843[/ATTACH]
*pic owned by tubeampdoctor.com*

After having to replace fractured 6550's where the spring/clamp joints are in tensioned contact with the glass, and enough travel time in equipment trucks, I've been using McMaster-Carr # 3038K14 Hi Temp 3/16" id/5/16" od 1/16" wall silicon rubber sleeving, slipped over the spring/clamp joints, as well as on the wings. 6550's don't need the wing sleeves per se, but the KT88's do benefit from them, helping the clamp 'hat' centering.



I havne't tried any thinner wall material on the 'wings'. First tubing I tried was too thick for the spring/clamp joint....though it works fine for KT88 wings. I have that thinner tubing spec'd above on those joints in the photo above.

After going thru a number of SVT-CL's in our rental inventory, I came upon the latest two that hadn't ever been into the shop for any service. Apart from the usual totally loose XFMR mtg screws & standoffs, solder fractures on bias pots, etc, I found they changed to a toggle base clamp that does a nice job holding the tubes in place.



As far as the clamps go, I like them, though I haven't tried them on different KT88's and 6550's yet. But, on the SVT-CL, you almost can't operate the toggle on the rear three tubes, because the spacing between the front and rear row is too tight. Single-screw mounting. I haven't priced these....I've seen similar ones that are pricey.

[hodgy]

I haven't been on the production side of things for a year now, so I don't know whether or not they are using those grommets on current production CLs or not.
When I was building the Heritage amps, I found a huge bag of the grommets and used them for all of the HSVT-CLs until we introduced the Birtcher-style clamps. The grommets never had a part number and were never part of the BOM. I had a heck of a time trying to source more, but by the time I ran out we were implementing the clamps (I agree, they can be a pain to access, but they sure look snazzy).
They (the clamps) are available as a kit, I think for around $50-$60 for the set of 6. I see that Fliptops is selling them as singles.

[Tom Phillips]

Those base clams are very nice. I am familiar with them from old military electronics and high end commercial equipment and did not know that they were currently commercially available. I have a stash of those style clamps that I saved when parting out old equipment. I have never installed any of them on customer's equipment because I was worried about the variations of base size of currently available tubes. I.e the fit may be good when the amp leaves my shop but not be correct when the tubes are changed at a later date. Never-the-less it's nice to know that the style is available. They would be nice for 6L6s and 6V6s too if an appropriate size was available. There would be the same issues with base size variations though since modern tubes do not conform to the original base, pin and bottle size specifications.

[nevetslab]

Fabricated Grommets from Hi Temp Silicon Rubber tubing

I ordered more Hi Temp silicon rubber tubing from McMaster-Carr, having depleted my thin-wall tubing stock I was using for the spring/top-hat clamp fingers, so while there, I added two small ID tubings....both 1/16" ID, and 1/16" wall thickness, differing with the OD...one was 3/16" OD, the other 7/32" OD. I had ordered the smaller ID in black, but it looked good. I've just made a set of top hat grommets using the 7/32" OD tubing, which works well. Here's the process and the results:



On this particular Ampeg SVT-CL, the hold-down clamp is the older style, having the lower-tension springs (having the hoop-hook ends), and the ID of the hold-down clamp 'hat' was 1.00" ID. Using McMaster-Carr P/N 3038K12 7/32" OD/1/16" ID/1/16" wall thickness, after empirical cuts, the length to fit the ID was 3.375" long. Slitting was relatively easy, using a fresh X-Acto No. 11 blade, walking it up thru the center, keeping the cut straight....though it didn't really matter that much. Slipping the slit tubing into place was an easy operation, and once set in, it didn't seem to need any glue. Easy to center, and provided a good degree of cushion. 10 ft length was the minimum I could order, but I'll end up using the material on Marshall, Orange, Fender, Ampeg, etc etc in our backline gear inventory.

My first attempt with the 3/16" OD Black tubing was difficult, having used a single-sided razor blade instead of the X-Acto No. 11 blade. There wasn't any difference in cost ($8.80 per 10ft). The smaller tubing was also available in translucent as I used here. I'll give that material a run next week.

In the background of the SVT-CL tubes/chassis, with the preamp sitting attached, some may notice the presence of Tech Flex sleeving in place of that awful clear vinyl 'garden hose' sleeving Ampeg uses. With the lead dress of the two harness cables, they're not in contact with the power tubes, and do have high temperature rating. I use it to allow easy positioning of the preamp chassis when I'm working on the amp outside of the case, while matching tubes (measuring voltage across the 10 ohm cathode resistors, with the amp stood up on it's side yielding access to the bottom of the main PCB.

[guitician]

It looks like you'll be running that rubber near it's limit of 392 degrees Fahrenheit... this thread I found shows one tubes side at 390...
Tube amps get pretty warm - especially in the summer (photo)

[nevetslab]

Fender SuperBassman clamps

Having to chase down a noisy preamp circuit in Fender's SuperBassman, getting the preamp out of that cabinet and back in when done requires removing the power amp chassis (Fender has 3 screws that thread into the top of the case from inside, with the power tubes in the way). Another 300W, (6) 6550C power tube amp, with similar but different spring hold-down clamps. After replacing a noisy IC in the preamp, I removed one of the hold-down clamps, noticing they had a large flat neoprene washer under the clamp. Upon lifting the clamp off the tube, I suddenly was greeted with 4 discrete parts.....the two springs fell off the clamp and also came free of the chassis holes, and the black neoprene washer also fell onto the chassis, leaving the clamp in my fingers. Never use a single assembly when you can do it with four discrete parts that wanna go their own direction, I guess.

Anyway, I thought this would be a good excuse to try out the slightly smaller dia (3/16" OD) hi temp silicon rubber tubing I bought from McMaster-Carr (P/N 5236K21 3/16" OD, 1/16" ID, 1/16" wall thickness), and slip them into the ID of Fender's clamp. 0.95" ID on the clamp, so the tubing length ended up 3.30" long. Same slitting method used...X-Acto No. 11 Blade run up thru the center hole. slips into the ID of the clamp and stays put just fine. The springs on Fender's hold-down clamps have 3/4-closed hoop hooks on each end, though from time under tension, they had stretched a bit. I re-shaped the ones that were opening up, then slipped them into place on the clamp 'hat' and slipped on 5/16" OD/3/16" ID/1/16" wall silicon rubber tubing that I've been using for the past year (McMaster-Carr P/N 3038K14) on all the hold-down clamps to protect the tube glass from the spring/clamp joint. Those three moves made the clamp a single assembly again. Now I just had the fumble-factor of getting the other end of the springs to register in the two pair of holes in the chassis.



The neoprene washer (I presume that's the material) is 1-5/8" OD, 3/4" ID, 1/16" thick. They seem to stand up to the task quite well. Just one more part to juggle as you're slipping the clamp over the tube, while trying to keep the two springs' hooks from coming out of the chassis holes down below.