Ampeg b-15r flip-top claw bolt maintenance

[nevetslab]

I have an Ampeg B-15R PortaFlex Combo Amp in the shop for Preventative Maintenance. After going thru the amp itself, curing front panel PCB control solder fractures, then pounding out all the dents and abuse to the tube cage, and, finding one of the four 6L6GC power tubes was only running 6mA against two @ 34mA and one at 31mA, installing new matched quad set of J/J's that landed at 38mA each, I finally turned my attention to the cabinet and the hold-down clamps and square bolts threaded into the flip top.

First, one end of the 1/2" wide 5/16" thick neoprene rubber gasket material is missing, with the rest that's present full of tears, and probably needing complete replacement, the one area of these that has always left me puzzled is the hold-down clamps. None of these when I began were holding anything down...totally loose, with three of the square bolts threaded into the flip-top plate rotated to place the corner upright, so there'd be a bit more height to pull down on....which only served to distort the clamps.

These clamps are cheaply made, nothing precision about them, and are held into the cabinet with long #6-32 pan head screws and keps nuts on the inside of the cabinet. I thought about it, looking at these, and wondered what do I have in my tooling to both straighten the clamp face where they engage the square bolts, and then, how can I increases the clamping force without having to drill new holes to mount them.

I pulled out one of my larger machinist clamps, opened up the jaw, grabbed a hole reamer to use as a tightening handle, and positioned the cabinet clamp so I could pull that shape down at an angle, hoping it would apply more pulling power onto the square bolts. I also rotated those bolts so they were level, and not with the corners face up. That seems to do the trick.



Now, not being able to find my left-over roll of foam rubber gasket material, I'll see what I can find at Home Depot. I also need some edging for the base of the perforated tube cage, as at present, the two long hold-down bolts (made up from acorn nuts & # 6-32 threaded rod with a flat washer on top) they're tightened down as much as I dare, before they get distorted. I used to have a rubber gasket material to slip onto 1/16" panels such as the bottom of the tube cage. Couldn't find that exact material at McMaster-Carr, but found something similar that might work. I also didn't find any good selection of suitable 1/2" wide foam rubber gasket, adhesive backed similar to what Ampeg used.

Better than it was, for certain.

[Leo_Gnardo]

Now, not being able to find my left-over roll of foam rubber gasket material, I'll see what I can find at Home Depot.

Parts Express offers two varieties of "weatherstrip" type material, small dimensions meant to be used as speaker mount gasketing. I always keep a roll around, it's good for all sorts of things and IIRC I've used it on flip top cabs.

For the bottom of the tube cage, possibly some thin rubber fuel line split with a razor would suffice. Hold in place with a couple dots of contact cement or weatherstrip adhesive.

[J M Fahey]

Congratulations to both of you and it was certainly a labour of love

Don´t worry about "lost" foam material, it´s probably crystallizing or gooeing by now.

[Randall]

I have never seen a B15 with four 6L6s.

[Leo_Gnardo]

I have never seen a B15 with four 6L6s.

I vaguely recall a St Louis Music early 90's version, perhaps this is one.

[nevetslab]

Flip Top Replacement Foam Rubber installed

I vaguely recall a St Louis Music early 90's version, perhaps this is one.

I too only remembered the one-pair of output tubes on these amp. Lifting up and out the amp head mounted to the shock-mounted top wasn't trivial. There's nothing to grab hold of, and this sucker is HEAVY. Those two encased transformers reminds me of a McIntosh MC75 Rack Mount Mono Amp (Sunset Sound in Hollywood used those for years in the old days). These at least are VERY WELL MOUNTED, and the mtg hardware for these xfmrs ARE accessible without having to tear everything apart, unlike the SVT-VR or SVT-CL. I bet they're ever bit as heavy, maybe more.

Anyway, today after walking thru, looking at and passing on everything I saw in Home Depot, I stopped off at my local DIY Center on the way to the shop (after stopping at a Kragen Auto Parts store to see if they had anything), and found some 1/2" wide x 3/8" thick similar compliance closed-cell PVC Foam, adhesive backed. I chipped off the old left-over adhesive from the one side missing the foam, applied a strip of this material, put the un-loaded top on and pulled the latches down, and it now pulls the top down into locked position. Great. I removed the other side, cleaned that up and installed the second strip of this new material, and mounted the top again. Looks like a winner. I haven't removed the long front and rear strips thus far.

Then, after seeing the clamps are now pulling the top down as they're supposed to, I flipped the top over for the amp mounting side, and carefully moved the amp chassis into position. Moving that is tricky, as there's nothing to grab hold of, unless you have huge strong hands and can lift it up by those transformers! Not with my small hands. So, got it mounted and took some more photos of it.



As there is a chassis hole open above a pilot light inside the chassis, I think there's an Ampeg Logo Plate missing from the tube cage, as the photo on the Owner's Manual shows one that looks a bit back-lit, like maybe it's a lexan panel that lights up.

Now, I just need to flip this cabinet over (after removing the amp assembly lid) to see if there's hardware missing from the caster plate.

The controls are much like that of the SVT-CL. No bias adjust on these....fixed bias...just lets you select -50V for the 6L6GC or -40V for EL-34 power tubes.

[Ted]

This is a B15R 90s (maybe even early 00s).
I seem to remember you could use EL34s in them with a biasing switch.

They didn't sound much like a B15N

[Enzo]

B-15 dated 1997.

Indeed has a 6L6/EL34 switch, Not adjustable bias of -50 versus -40 volts.

Has a half power switch lifting the cathode of two power tubes.

4/8 ohm output switch.

[nevetslab]

Finishing up with this B-15R Flip Top, with the lid in storage mode, amp hanging upside down inside, the lid handle had broken underneath. Good place to use Lacing Tape. So, I started at the short end, near the metal mounts and began making clove hitches, drawing the lacing tape taught at one side of the handle, and worked towards the break in the bottom. Then, did the same at the other end, and had a solid comfortable handle again.



In this storage mode, I also found one of the flip top claw latches was loose (though wasn't with the panel reversed with the Amp sitting on it at the ready). It made me want to go find thicker foam rubber sealing material. But, I thought maybe I'd try some heat shrink tubing over the square bolt heads first. Before I even got to my shrink tubing, I first checked my stash of cable jacket tubing. I save that material, as over time, I find it comes in handy. I had a piece with 0.045" thick walls, ID about 0.410", and cut it straight for starters. I had to push it on over the square head, so that was good...it had a nice snug fit. Pushed it to where it bottomed out against the edge, then cut it off a bit beyond the head with an X-Acto knife blade, and tried that. It added enough size to cure the one claw, and the rest pull the panel down ever more.....every bit helps with these things.



I looked again on McMaster-Carr this morning to see if I could find something close to what Ampeg used for that foam rubber seal on the cabinet. What I don't have is the Shore rating of the material. I used to have a Durometer that read in 'A' Shore Hardness, but sold that years ago. Foam rubber uses a 'OO' scale for hardness, and, I wasn't finding any ratings on the various closed-cell foam rubber materials in their list, and gave up, settling for what I had found empirically this past Sunday, as it is very similar to the original material. Good enough, at least, and the clamps are pulling down even tighter now.

Enzo is right. This model DOES have the 100W/60W power switch (opens the cathodes of two of the four power tubes), has an 8 ohm/4 ohm impedance switch, and the BIAS switch for selecting EL34 or 6L6 power tubes. Also has a NL4 spkr connector along with 1/4" Jack, though the speaker connection plate is 1/4" only.

[TimmyP1955]

The latches on the latest B15s are very wimpy. Wish I could figure out a substitute.

Now I know what those funny clamps are that I've been looking at for the last 15 years.