Anticipating chassis flex - multiple heavy transformers

[pjd3]

Hello,

Has anyone ever had to hunt down a solution to "amp chassis flex" due to heavy transformers and/or thinner or weaker chassis?

Reason I ask is that it looks like chassis could be made thinner these days to save on metal, and also should there be say, a big heavy power transformer that has to be in the middle of the chassis or multiple transformers for stereo amps.

I've seen fairy heavy U bars and L bars in Home Depot and wondering if anyone has ever utilized things like this to address undue flex in an amp chassis.

Thanks,
Best,
Phil d

[didit]

Hello --

Hammond 1444 series aluminum boxes are a preferred affordable and easy to machine "blank slate" that, with a few suitable hardwood strips for reinforcement, can impressively accommodate fairly beastly iron. No doubt some extruded aluminum stock would also work well.

Best ..

[pjd3]

Thanks didit,

I will take a look at those Hammonds, and it seems as though those extruded bars will help with that if installed in a good place.

Awesome, thanks! I'm well into the building a few stereo tube amps, some with double PT;s and others with one big huge PT in the middle. Don't want to invite sag!

Thank you,
Best,
Phil D

[nuke]

In aircraft, stringers and hat-section segments are riveted into make thin aluminum skins strong. It's actually pretty easy to rivet aluminum, you can use blind rivets or solid rivets. If you use blind rivets, get the strong ones for race cars and aircraft, not the crappy pop-rivets from a hardware store.

[lonote]

I have added a fitted secondary plate on a few. Stiffens things up quite a bit.

[R.G.]

Buy a length of either aluminum or steel L bracket. Find a path under the chassis to put a length down the whole chassis. Bolt or pop-rivet this in. The length will be much more stiff from the support of the new bracket. The width will be much stiffer because the two smaller sections are - well, smaller.

[pjd3]

That ring plate around the transformer looks like it would help to stiffen things around the transformer, that might be a little hard to come by or make, well, for me it would. (there is a milling machine in our company shop, though. )

The idea of an L rod (or U) along the width of the chassis was more of what I was envisioning, especially nearing the back where all of the transformer weight is. Thats what I'll probably do, fit one or two of these in open areas of the chassis rears with little bolts. Home depot has a fair selection of those in different sizes, and there is a choice of Metal or Aluminum. The metal bars are notably heavier but, I have to wonder if they would allot for more stiffness than their aluminum counterparts.

I'm making plans for another stereo amp for next year project and it will probably entail a 400mA 360-70-0-360 PT in the dead center rear of a 24" chassis. I'm pretty sure this will benefit with something to support a 12-14 lb power transformer.

Thanks guys,
Good ideas.
Best,
Phil D

[sluckey]

Back in 2006, after a 30-year hiatus from amp building, I renewed my interest and stepped back in. So, I bought three Hammond 1444-20 aluminum chassis because they were a perfect fit for a 5E3 combo amp. These chassis were 17.00 x 4.00 x 3.00b but only .04" thick! That's less than 1/32"! Machining was easy but I could literally twist the chassis like a pretzel bare handed. But they were affordable.

These 1444 series chassis are OK if they will never be moved. But throw it in the back seat or the trunk and it's just a matter of time before the chassis will fail. Sure, you can beef it up a bit with L-brackets or wood blocks, but then it will look like an old cheap Valco. Why bother. Just get a .08" or .09" chassis and don't look back. And don't worry about normal wear and tear.

[didit]

Hmm --

Aluminum is easier to work with and quite rigid. Steel has specific strengths, but those seem less helpful in this application. And also some concerns about steel having higher tendency to carry stray inductance. My shop inevitably has scraps of maple and other hardwoods, and plenty of "baltic" birch ply offcuts. These I find are both easily shaped and fastened in.

And now we're down to diss'ing the venerable Valco and their brethren.

Best ..

[Phil_S]

Interesting discussion... I suppose it comes down to individual skills and preferences. Certainly, if the thicker aluminum is available, that's the easiest and most straight forward thing to get, particularly if you don't have skills, tools and equipment, readily available materials, or simply no desire to beef up a thin chassis. OTOH, many of us are DIY types and probably enjoy Macguyvering the thin chassis at a low out-of pocket cost. Choose your path.

[R.G.]

Side notes:
Like steel, aluminum has various alloys and heat treatments that dramatically affect its strength, rigidity, and brittleness. The 606x series of alloys are the most common, and are a good compromise for general stuff, much like mild steel alloys are for steel.
Steel and aluminum are (in general) related by a factor of three: aluminum is 1/3 the weight, 1/3 the strength, and 3 times the price for a given piece and same dimensions.
Aluminum is indeed easy to work. Some of the nearly-pure alloys are - literally! - feasible to shape by whittling with a pocketknife. They're too soft to be anything structural. Pure aluminum is similar in consistency and workability to some of the harder varieties of cheese.
The aluminum bronzes are quite sturdy, and compete well with softer steels. But you won't find chassis made from this. A given aluminum chassis is probably a 606x alloy, commonly 6061 or 6063, with a T3 or T6 tempering for more structural strength.
For a fun look at aluminum and its alloys, see: https://www.cabww.com/wp-content/upload ... lum-wp.pdf

[Stevem]

1/8” thick aluminum bar stock available at 95% of hardware stores would my pick to reinforce areas of the chassis.

Cut it so it fits in crosswise front to rear assuming the chassis is longer then wider.

The bar stock can be drilled and taped for 6/32” machine screws easily and you can also drill wire pass thru holes in it and line those with deep type pressed in bushings should you care too.
I once did this to a Highwatt 200 that was going out again on tour after just about coming to me looking like it was hit by a train due to a cheap travel case being employed.

I screwed a near 5” long section of this bar stock under each massive transformer and then used two sections of the bar stock top side that the transformer stood on so as to both clear the screws used to clamp the bar stock the was on the inside and really add massive stiffness.

It took me 6 hours to do that job due to wiring. but if your starting with a bare chassis with good drill bits and a vise your looking at a hour and 30 minutes at most.

PS.
Also you can cut V notches into the bar stock for wiring if you don’t want to drill holes.
I did both which really helped out with the wiring .

[jabguit]

These chassis were 17.00 x 4.00 x 3.00b but only .04" thick! That's less than 1/32"!

1/32" is 0.03125" Still 40 thou is thin.

cheers,

[Roe]

reinforced corners also helps

[nuke]

Buy a length of either aluminum or steel L bracket. Find a path under the chassis to put a length down the whole chassis. Bolt or pop-rivet this in. The length will be much more stiff from the support of the new bracket. The width will be much stiffer because the two smaller sections are - well, smaller.

Yes to bolts and machine screws, no to pop-rivets from the hardware store. Those pop-rivets, even the steel ones, are very weak and you can rip them out with your bare hands. Just won't offer any long-term strength.

If you use blind rivets, use Cherry rivets as used in aircraft or race car construction. They're not as strong as a driven solid rivet, but they're far superior to a pop-rivet. Unfortunately, such rivets and tools are pretty expensive. Unless you know someone who builds race cars or homebuilt airplanes and already owns the tools.