New Hold-down clamp for EL-84 Power Tubes

[nevetslab]

The Belton 50703 Hold-down clamps arrived today, so I sat down with those, cut some of the 3/32" ID hi temp silicon rubber sleeving to the circumference of the hole in the hat (1.85" long), slit it and rolled it into place, so that fits nice and snug, seating the top of the EL-84 tube. I used the 3/16" ID hi temp sleeving to fit onto the four fingers of the clamp 'hat', making the two with the springs a touch longer to cover up the spring/finger joints. Bent the four fingers in a touch so they'd cradle the sides of the tube.

I had a collection of the mounting flanges that is received with the new thin spring-wire hold-down clamps that everyone uses, put a 3/32" Taper Pin Reamer into my small tap wrench and opened the upper holes of the two mounting tabs for the spring wire clamps, just large enough for the Belton hold-down spring clips to pass thru. Installed a tube socket to the assembly to install an EL84 tube and took a look at the results.



The mounting flanges that come with the spring wire clamps is thin metal, and I suspect trying to open them up with a 3/32" drill may be a problem. Not so with the smallest taper-pin reamer I had. It did leave a burr, but that worked well getting the clip thru the hole. I had to use needle-nose pliers to hold the clip open to slip it thru the hole.



I also thought of using a short threaded #4-40 standoff or male-female #4-40 stud-standoff, with a a Keystone right-angle bracket or solder lug....still would have to enlarge the hole for those tiny clips to pass thru.

When I first saw these Belton 50703 clips installed, I was afraid the amount of tension I saw on the springs would be too much, but, actually not....just right.

Now, I need to get the Hiwatt Little Rig back here to the shop, as those have now gone into our rental inventory from Hiwatt, and remove the spring-wire clamps and install these, along with all of our Vox inventory and others that use that stupid spring-wire clamp. Never did like those.

The Hi Temp Silicon Rubber tubing.....the inside hole of the 'hat' uses 3/32" ID, 7/32" OD, P/N 3038K12 (10ft length), and the spring/tab & wings use 3/16" ID/5/16" OD, P/N 3038K14. McMaster-Carr. https://www.mcmaster.com/catalog/127/159/

[mozz]

I'm missing something, was there a problem with them that you had to use the silicone? Microphonics maybe or tube breakage? I typed the model number in Google but do not see anywhere to buy them.

[nevetslab]

I bought the Belton 50703 from www.amplifiedparts.com. I also just googled Belton 50703, and found them at there at amplifiedparts, Stewmac and Antique Electronic Supply, as well as at Tube Doctor. Typically $1.95 US price.

The silicon tubing is there for shock mounting, getting metal off of the glass, and....these hold the tubes in place far better than those flimsy spring wire clamps. Over time, those wire clamps leave the EL84 tubes plugged into Vox AC30's really sloppy & loose. I haven't had breakage with them, but on the larger tubes, such as the KT88's and 6550's, the spring/hat mounting joint has many times dug into the side of the glass and cracked the tubes, taking the amp off the air. All of our inventory using 6L6's, EL34's, KT88's and 6550's have the added hi temp sleeving added which has reduced the tube failure on touring amps.

[mozz]

I'm not signed in on Google so it takes me to page 3 before i see a Stew Mac link. All the way up to page 10 i see no other links for those. Now if i put the same plus the words tube retainer i see the other stores.

[nevetslab]

I'm not signed in on Google so it takes me to page 3 before i see a Stew Mac link. All the way up to page 10 i see no other links for those. Now if i put the same plus the words tube retainer i see the other stores.

Clicking on the link to www.amplifiedparts.com, click on Browse all Parts, then go down the list to Vacuum Tube Accessories, and it's on Pg 3 of that section, 3rd item on that page. https://www.amplifiedparts.com/produ...ssories?page=2

[Chuck H]

I've done something similar a couple of times due to microphonic tubes. I used silicone o rings and sort of loop de looped them along the side springs and then a silicone washer/gasket at the top. It made a difference worthy of the effort but it's better if you can find tubes that don't rattle. I got into a batch of old Russian 6p14p tubes with the "K" designation. Which means they're built and selected for low microphonics. I have to say they've been holding up very well in combo's I know that really beat up the plain ol' el84's.

As to glass breakage... Wow. If an amp is getting knocked around such that the tube mount springs are cracking the glass then the real problem lies elsewhere IMHO.

[nevetslab]

[QUOTE=Chuck H;n947379

As to glass breakage... Wow. If an amp is getting knocked around such that the tube mount springs are cracking the glass then the real problem lies elsewhere IMHO.[/QUOTE]

The glass breakage was on Ampeg SVT-CL's and SVT-VR's using 6550's. The spring-tab joints at the HAT had that sharp joint under tension at the side of the glass bottles, and I'd periodically find a tube frosty white from that joint digging far enough into the glass to cause a crack. I've published those images before. And, I've seen equipment roadies take an SVT road case inside the truck, quickly flip it upside down with a loud jolt on the truck bed to keep it from rolling, then heft it up onto another road case. So, taking a very dim view of that sort of treatment (and reporting them to our general mgr), I finally adopted the hi temp silicon rubber sleeving on the hold-down clamps. I've never had such occurrences with EL84's, of course, but, have had loose fitting EL84's with the weak spring-wire clamps on Vox amps and others, so I have been looking for a better clamp for those tubes for some time. When I saw the Belton clamps, and finally got some to work with, these look like a better solution for firmly seating them into their tube sockets. Perhaps the sleeving is overkill, but it gets the tension off of the glass.

[mozz]

I've done something similar a couple of times due to microphonic tubes. I used silicone o rings and sort of loop de looped them along the side springs and then a silicone washer/gasket at the top. It made a difference worthy of the effort but it's better if you can find tubes that don't rattle. I got into a batch of old Russian 6p14p tubes with the "K" designation. Which means they're built and selected for low microphonics. I have to say they've been holding up very well in combo's I know that really beat up the plain ol' el84's.

As to glass breakage... Wow. If an amp is getting knocked around such that the tube mount springs are cracking the glass then the real problem lies elsewhere IMHO.

I think i also bought some of those, probably from a guy on here? 6P14P-K, i know they were not the -EV types. What would you consider the max plate voltage? Running el84 above 300 usually gets me worried.

[nevetslab]

I had used some of those Russian 6P14p power tubes on the Magnatone M15 Stereo combo amp I restored back in 2010. I came upon this data sheet back then:

6P14P-Russian 7189A.pdf

The 7189/7189A tubes also have higher plate voltage max ratings than the EL84's. I can't say I've found loads of failed EL84 tubes in the Vox AC15's and AC30's over the years, which are putting plate voltages above 300V on them, though they are cathode biased, so it does lower the full potential.

Here's a couple images that started me into making use of the silicon rubber sleeving to combat the failures I was finding on 6550's in Ampeg SVT amps:

[Chuck H]

I think i also bought some of those, probably from a guy on here? 6P14P-K, i know they were not the -EV types. What would you consider the max plate voltage? Running el84 above 300 usually gets me worried.

I actually like the way el84's sound when run high. They really tighten up on the low end and the inter modulation distortions seem to be reduced. So they hint at something more like little big bottle tubes than the classic el84 sound. I've built a couple of 300-ish voltage el84 amps just to hear the mojo and to be honest it didn't ring my bell entirely. But I did get the appeal for some players styles. And I do like a little of that "el84 tone" to come through.

I usually run el84's over 350Vp. My personal el84 amp has 370Vp. It's cathode biased so the actual working plate voltage is about 355. For my own preferences this is the sweet spot for this tube. It still has some of the classic el84 compression and complexity but it punches and bites a little more. JM2C on that.

So... The 6p14p-k tubes I'm using last about a year in said amp with moderate use. This is unheard of for most other el84's I've tried. Market standard el84's only last about four months in this amp.

FWIW Traynor, Mesa, Peavey, Matchless and others run el84's at or over 400Vp all the time. Traynor, Mesa and Peavey in fixed bias. El84's aren't the most expensive tubes to replace so my motto has always been "Smoke 'em if you got 'em."

[DrGonz78]

Yup I am with Chuck on the sweet spot for EL84’s. Just converted and built another EL84 amp. It was and old AO-43 organ amp I picked up on fleaBay. B+ voltage is 383v and cathode to plate is right about 363v. Of course cathode biased and really screams. I am using the old Conn EL84’s that came with the amp. I have some 6p14p-k tubes to try out after those wear out. I initially put in some cheap sacrificial tubes when I was first testing it out. Those tubes were not drawing much current and sounded pretty sterile. My first amp, which Chuck and other members here helped me along, did not have as high of plate voltage. I remember using a zener diode string to reduce plate voltage on it. It sounds good but this new one sounds even better.