Chassis questions

[Ty_Bower]

I'm thinking I'd like to use one of the Hammond black powder coated steel chassis for my DIY ST35 project. I plan on using a small drill press with a unibit to cut the holes. I'm not planning on using a tube rectifier. I'll probably go with all Hammond transformers, using the 270HX for the power supply. My line voltage tends to run a bit on the high side.

I can't decide if I'm better off with the 12x8x2 chassis, or if I should go with the 12x10x2 for a little extra space. There seems to be a cage that fits the 12x8, but none for the 12x10. It might be nice to have a cage...

After I drill out the holes in the chassis, does anything need to be done to prevent rust? There's going to be an exposed edge where it got drilled out. Do I need to repaint the whole thing after drilling? Should I forget about steel and go for the aluminum chassis instead?

[mesherm]

Everything will fit on the 12x8.
The black steel chassis can be worked with a good high/low speed hand drill and unibit. Put an old towel or something on the work surface but DON'T drill through the chassis and let the bit grab the towel... Yellow_Light_Colorz_PDT_09
I center punch the hole locations then drill a pilot hole with a 1/16 to 1/8 inch drill and finish it with the unibit. Otherwise the unibit tends to wander. If you have room, use the unibit on the reverse side of the hole to deburr.
A word of caution, sometimes as your drilling, the steel shavings will spin around with the unibit and scratch the painted surface around the hole.
Square holes are best made with a Dremel and the fiber reinforced abrasive cutoff wheels.
I have not had any problems with rust but I live in SoCal where it is dry most of the time.

[TomMcNally]

I've used dozens of these, and have never seen any rust (yet) ... you could get a bottle of automobile touch up pain (I have some from my black Honda) and run it over the exposed steel if you want.

I built an ST-35 in a 12x8x3 ... looks great ...



The best bet is to use the unbuilt circuit board as a template ... lay it on top of the chassis and drill the corner holes, one at a time, then bolt the board in place, then centerpunch and drill a pilot hole in the tube socket holes. Then remove the board and use the UniBit (cutting oil is helpful) Make sure you set the board back from the edge another 1/8" more than I did in these pics. I used a Greenlee Chassis Punch and distorted the front corner a little bit. Not bad, but I know it. As you can see, there is lots of room. I'm not sure if it will all fit in a 2" deep chassis though.

More Hammond Black Chassis pics on my website at http://tmamps.com

[EWBrown]

I've done it with 12X8X2, though you have to watch the height of those 120uF 450 V caps, and use spacers about 3/8 inch. (Half inch worked but it was a close fit to a bottom plate).

12 X 10X 2 or 3 goves you a little more "wiggle room". With an even wider chassis, the OPTs can be mounted at the ends of the PCB, makes inner wiring a lot cleaner, and allows good spacing away from the power trannie.

I think I still hold the record for cramming a DIY 35 onto the smallest chassis, 10" X 9" X 1.5", using the Triode UL Fender OPTs, and top-mounting the board, so only the C345 choke and some AC primary wiring, and some incidental I/O wiring, is under the chassis. Not recommended if there are toddlers or kittens around the house...

/ed B in NH

[RuralUrban]

Ty_Bower,
With a little research on the Hammond site, I found out that the 10X12X2 chassis (Suffix number -29) does have the matching cage assembly, as I just got one delivered last week. They are really nice chassis, I got one since I am waiting on the Soundtastick chassis from Triode which are currently out of. I was hoping the 2 inch depth would be OK, since the Soundtastick is even shy of that (?) Not sure if I'm going to use it for my ST-35, as I am going to play with a pair of the AES monoblocks with the triode/pentode tubes and all the mods, while I'm waiting on the ST-35.
Anyhow, for those that like those Hammond caged chassis, they do make a cage for the 10X12, just a little harder to find vendors that carry them. The folks I got mine from directly ordered it from Hammond, as they offered it but didnt have it in stock, only took them two days to get it to me.

Thanks to all of You here who have already given me a huge education on how to have fun with this stuff,

Russ

[TomMcNally]

By the way ... a tip for you kitchen counter metalworkers ...

Those last quarter Mouser Electronics catalogs, which are now about
two inches thick, make a nice drilling base. Just shake the filings
into the trash can after you drill each set of holes to avoid scratches.