EL84 tube clamp, in a pinch......

[nevetslab]

While going thru our rental inventory's stash of Vox AC30-6/TB combo amps, I came upon one with a solid state Groove Tube rectifier module installed in place of the 5AR4. During the preventative maintenance work on these, I was correcting the wiring on the rectifier's output, where the factory had wired the HT load off pin 2 (heater) instead of Pin 8, being the other side of the heater coil AND the cathode. And I've removed the switched plate leads to the rectifier, that have been the Standby function, spliced each together, and instead, open up the power tube's cathode circuit (summed cathode buss to the cathode resistor/cap network) for the Standby function.

Not wanting to have the SS rectifier module in place, putting HT onto the plates of all the preamp tubes before they've warmed up, I went to install a 5AR4. Hm.... no hold-down clamp.

Pulled the chassis from the cabinet, and found besides there being no clamp for the 5AR4, one of the EL84 tubes was missing it's spring-wire hold-down clamp. Figures I ran out of those and hadn't ordered more.

After ordering those, and not being able to find any 6V6/5AR4-sized hold-down clamps...resorting to the bear-trap clamps for the time being, I thought about the EL-84.

Grabbed a bottle cap from an empty lemonade bottle, punched a hole in the center & two on the sides with a Whitney punch, fetched my stash of 3/32" dia shock cord (for restoring condenser microphone shock mounts' elastic suspensions cords), some aluminum ferrules and a paper clip, and fashioned a temporary hold-down clamp:



Hate having to leave an amp in pieces waiting for parts. Should do the trick for the time being. The white thingies on the 5AR4 clamp hat is silicon rubber tubing, that I've taken to use on the clamp hats these days, having tired of replacing tubes that end up with fracture holes from contact with the hold-down springs, driven by vibration in the tour trucks.

I didn't use them on that flange that mates up with the spring on each side of the clamp hat.....that spring/flange mating has normally been in direct contact with the straight-body 6550 tubes (see photos below, and has caused fractures of the glass bottle, as seen in the following photo, Then, photo of the cushioned clamp on some KT-88's, which have the tapered top shape to the bottle.

[Leo_Gnardo]

not being able to find any 6V6/5AR4-sized hold-down clamps.

I just cut the springs shorter. Bend the metal at the top of spring-clip to fit shape of tube top.

Haven't yet had any tube glass shattered from spring contact. Color me lucky.

HAVE had wafer-base 5881 Sovtek glass split by being hammered with edge of bear trap tube retainers. This combination does not get along well at all.

Spring clip trick: I can occasionally hear noise from the springs come thru the tubes, like a very bad reverb. Cover springs with a layer of heat shrink tube. Damps the noise, acts as a cushion between springs and tube side glass, stays well- shrunk with tube heat. Haven't had any crack in the heat or catch fire. Yet. I use 3M HST from Mouser. Other types may be less successful.

[TimmyP1955]

That bottle cap is gonna melt some.

[nevetslab]

Chances are the replacement clips will arrive before anyone selects that amp.....we got 10 in our inventory. Yeah...I had thought about that

[drewl]

Its easier to use some buss wire, wrap it around the tip of the tubes point and fasten each side to the socket mounts.

I've done this on several old amps that don't have retainers, especially like the old Fender Musicmaster bass amps.

[Pedro Vecino]

In AC30 with horizontal GZ34 I do not use anything. I consider more functional its light tilting movement that to be fully fixed to chassis. It works better the natural suspension that the stiffness.

[nevetslab]

Of the 10 AC30-6/TB's we have in our rental inventory, only a couple have their 5AR4 tube sockets secure enough that I'd feel comfortable letting go out on the road without hold-down clamps or bear-trap clamps, even in the road cases. The physical condition of the Tolex covering on half those amps are in is shameful. Must be an unwritten rule out there.....if it don't belong to the band, trash it! Still, seems like they hold up better than the Marshall JCM2000's do.

On those make-shift hold-down clamps, I chose to use paper-clip steel, as it has far more temper to it, holds the hook shape better than tin-plated copper buss wire. I thought about hacking off some length of the standard 6L6-sized springs, but would rather have the machine-cut shorter spring than the modified longer spring.....end-wrap of the spring coil is better.

[Leo_Gnardo]

I thought about hacking off some length of the standard 6L6-sized springs, but would rather have the machine-cut shorter spring than the modified longer spring.....end-wrap of the spring coil is better.

I just chop the spring to needed length then use "dikes" wirecutter to pry 2 last loops away from the rest. Fits the punchout and holds as well as any factory cut spring. Nobody but the eagle-eyed spring inspector will ever know. The machine-spun ends look neat but looks is all, the appearance has nothing to do with their utility. Try one, takes a minute, whatcha got to lose? If your first comes out sloppy, no worry. Practice makes perfect.

Going the other direction, if I need extra long springs to hold in a 5U4 for instance, I just gently pull the spring until I feel it give a little. Yes I've overdone it a couple of times but dang if I'm going to order and stock tube retainer clips in long, medium and short. I'm enough of a haberdasher what with all the parts I stock.