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Hammond chassis mounting question
Hi all,

For mounting a usual Hammond chassis in a wooden enclosure MArshall-style, I use angled brackets mounted on the chassis using blind rivets where the whole construction is then fastened using bolts and screws, but I've always wanted to have a system that uses cage nuts instead...

How would you mount it? What hardware would you use?

P.S. Couldn't find a more relevant subdir, hope its is ok to post here. Wink
Formyx Amplifiers
Hi Guys

Cage nuts might be a little difficult for hobbyist to use since most such nuts (cage nuts not hobbyists) require a square hole.The return on the chassis may not be wide enough to provide much support the nut mount. Hammond's chassis in general can be a bit flexible when they are asked to support as much transformer weight as a medium-size tube amp is.

An alternative to the cage nut is the J-clip. In cross-section, a J-clip looks like a 'J' made out of a folded over strip of metal with a clear hole on one side and formed "half nut thread" on the other. Slip the J-nut over a round hole drilled in the chassis return. The J-clip spreads the load over a small amount of the return and again may not be the best means of securing a heavily loaded chassis.

With either the cage nut or J-clip, if one were to go beyond the traditional and intuitive four mounting points then either would be quite viable on stock Hammond chassis. Best to consult with the hardware catalogues to make sue the chassis return is deep enough to accommodate the prospective mount.

An alternative is to do what Traynor did with most of their tube amp chassis. They drilled pairs of holes lined up in the return and the top of the chassis, both near the fold for the side apron. A long bolt is passed through the amp sleeve and both of these holes, atop which a washer and nut can be tightened n. The washer should be larger than the nut so the compression forces will be spread out more. Traynor often used nuts with integral toothed washer to lock the nut in place, in addition to the flat washer suggested above.

Large diameter washers are often called "fender washers" - they won't clean your Fender amp or guitar, but are so named because of their use for automotive body repair and/or assembly. Some general hardware stores carry these as do specialty stores that carry extended varieties of mechanical hardware.

Have fun
Another thing you could do is install threaded rivets. It's fairly easy since you just drill a hole in the material and the use the rivet tool to install them. Habor Freight has a cheap one that works fairly well. You could some angle iron or joining hardware pieces used for roofing and attach those to the sides of the chassis with the threaded rivets installed on those.
Thanks for the input, guys!

Using cage nuts would require lots of filing after drilling since I don't own a square hole drill.
I have encountered J-clips on some cheap Marshall combos, but their construction did not strike me as reliable.

The Traynor way would be something to consider, though. In high gain amps it would also allow for aluminium sheets to not get in the way of contacting the chassis, so this is a consideration. This is something I have met in Fender combos where the bolt-nut holds the chassis up in its place.

Threaded rivets is a quite nice solution, actually. So using the aforementioned angles attached to the chassis with blind rivets, one can just vertically mount them so that they align and get tightened by a bolt from the underside of the wooden enclosure!
Formyx Amplifiers
Glad to help!
Hello folks!

I have a Hammond 4U rack, named RMCV190513BK1.

I wanted to mount a 382BX and a 1650-N on it, two heavy transformers.
It looks like this is not supposed to be done, the rack sags.

Is the only option to put the transformers inside?

Kind regards,

Hi Guys

The Hammond rack chassis are not really meant for the kind of weight that a tube amp over 50W might have - even at 50W panels will sag. Unfortunately, most of Hammond's chassis sizes that are useful to us are made in thin-gauge steel or aluminium - kind of ironic that their enclosures won't support their iron Big Grin

There is a more expensive rack series with extruded sides but I can't find the catalogue that was in. I suspect that because of the "4-screw easy panel removal" in the rack designs, that this would sag, too.

Placing the PT and OT inside a 4U chassis seems like what you would want to do anyway. If anything goes outside it should be the power tubes. Support needs to be beefed up using bent metal not just thicker metal. Think of an I-beam. The vertical web gives it strength and the top and bottom panels provide rigidity horizontally. if you had a U-shape where the bottom of the U is against the chassis panel, the vertical parts would help to keep the support plane from sagging. The U has to be fairly strong material itself, stainless or thick steel.

The added U above can be added inside or outside, since whichever panel the TXs are mounted to will sag. Seems like you were going to have them on top, hopefully tubes as well, so why so much space underneath?

Have fun
Haha yeah, they can't take their own power. Or at least the weight.
Hey, "The Weight"... that song... I can hear the chassis sing "You put the load right on me!".

I briefly considered putting in a support beam but that would just be fake: there would me too much tension on other parts.
Probably where I would least expect it.

The idea was to have the tubes upright and on the inside.
Just to be safe and for more air I opted for the 4U.
I have a panel on the bottom that you insert so that the screws go there and not at the bottom of the rack itself.

You say "the tubes hopefully on top", is that better than inside?

I chose 4U so they can fit inside and have some air.
Also the cover is ventilated.


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