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Old 10th April 2006, 11:10 PM   #1
Trout is offline Trout  United States
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Default Cooling In Cab / Minimum Vent Area?

Just about completed on some guitar cabs and began to wonder,
Exactly how much Cooling/Venting is needed in a Valve head.

I have all the tubes offset forward on the chassis and a fairly large front vent. Cab to - top of tube distance is fairly good.

You guys think I can use a solid back? or should it be vented similar to the front?

The Bottom of the back is cut exactly the same as the front to access speaker jack,Fuse, IEC cord.

I was thinking I might ommit the top vent on the back since there is good cab volume/area and ample front venting.

The Cab
The Chassis
Bottom Chassis View

Pulling that tweed around those inside oval cuts is a nighnmare!!
Opinions please
Trout
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Old 10th April 2006, 11:27 PM   #2
Sherman is offline Sherman  United States
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That's a pretty large vent area in front. I built a cab with no front or top vent but with an open back (a 5W EL84 amp) and I've been operating it for a few months with no problems. I pulled it recently and check voltages and currents and everything is pretty much where it was when I put it in.

That said I would still be tempted to make a vent on the back either right below or right at the top of the chassis. That should create a pretty decent airflow from back to front and from bottom to top. I think I'd just cut an opening in the back and attach a piece of perforated aluminum inside.
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Old 10th April 2006, 11:35 PM   #3
Trout is offline Trout  United States
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Quote:
I think I'd just cut an opening in the back and attach a piece of perforated aluminum inside.

I have more of that front grill/mesh. ( Home Depot Metal Gutter Guard)

The Thing is, I am trying ( hoping ) to avoid more holes. To make it look good/finished I would need to tweed wrap the inside edges like the front. Those are a nightmare especially on 3/4 birch ply.

I think had I used perhaps 1/2 inch or 3/8ths it would have been much easier.

Maybe I can get a plush mount type thing on the back that just screws over a hole.

I guess I can try it closed back, If I smell smoke in under 4 hours running, Expand the cooling area.
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Old 11th April 2006, 12:22 AM   #4
poobah is offline poobah  United States
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Gene, kick this around...

Make a new back panel out of 3/8" material. Put some 1 x 7 (?) x 3/8" strips on the inside face at eacn end to regain the thickness.

Then, cut your lower access notch just like you planned. This will create a 3/8" gap that will allow cool air to come in the bottom and flow out the top.

Next amp; reverse this setup front to back and you'll have someplace to screen the "TROUT" logo.

There are some tricks to doing holes like that... even in 3/4". If you are laying the material on the flat and then pulling the holes in... that is exactly backwards... unless of course you have a big neighbor named Gunter with thumbs like cuccumbers. Lemme know...

LOOKIN' SWEET DUDE!
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Old 11th April 2006, 01:13 AM   #5
Trout is offline Trout  United States
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Quote:
Next amp; reverse this setup front to back and you'll have someplace to screen the "TROUT" logo.
Actually, My gal and I have been kicking around a couple logo Ideas.

1 is an Blue LED backlite logo panel in the center bar, The other is a molded script logo mounted to the front mesh.

The Chassis, and Cab style is going to be used in my 6 - 6550 PP projects for my brothers band during their summer of gigs.

Thats a huge chassis, 17 X 10 X 3 inch which leaves my a lot of expansion room.

I have a pair speaker cabs framed up but not covered yet, Nice home for the 4 X 12 Greenbacks.

Plus were putting a couple on ebay to defray the costs

Trout

BTW, This is the first time I have ever worked with tweed covering, Its Thick, Stiff, Terrible to mold around corners, and soaks up glue faster than a sponge. Credit to the people of yesteryear for making it look so nice and simple.
Quote:
If you are laying the material on the flat and then pulling the holes in... that is exactly backwards
Well Um Yes and no, I pressed it into the inside cutout as far as possible without wrinkles, Then rolled it out on the front.

I am able to get about 1 /2 inch into the hole without score cuts, Then it gets impossibly tight .

I figure I might rout out a 1/4 -3/8s pocket into the panel from the back, Then wrap it , Pop in the grill and hopefully fix the issue.
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Old 11th April 2006, 01:17 PM   #6
Sherman is offline Sherman  United States
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Quote:
Originally posted by poobah
...makke a new back panel out of 3/8" material. Put some 1 x 7 (?) x 3/8" strips on the inside face at eacn end to regain the thickness.

...cut your lower access notch just like you planned. This will create a 3/8" gap that will allow cool air to come in the bottom and flow out the top.
I like that idea myself. Makes things simpler and simpler is usually a good thing, and 3/8" is still too small for fingers to get in and touch things they shouldn't!
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Old 11th April 2006, 02:31 PM   #7
Trout is offline Trout  United States
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Quote:
I like that idea myself. Makes things simpler and simpler is usually a good thing, and 3/8" is still too small for fingers to get in and touch things they shouldn't!

Its sort of hard to see, But there is actually metal mesh over the cooling opening/s.

Its made from gutter guard from the home depot warehouse home improvement store. 4 ft for 1.95. I painted it with black epoxy paint.
The unit has the mesh front and rear. I just finished (covered) the back panel which is exactly like the front. (just removable)

I may have to re-think the layout on the chassis, Tube swapping will be a bit difficult on the Rect and 12AX7's because they are so far forward. But then again, It might not be that big of a deal, They should last a year or so (hopefully).

The Next cabs most likely will have 1/2 inch stock front and rear. I love the 3/4 recess on the controls, It offers some bump protection, But it is really hard to cover.
Tolex would have been much easier, but the tweed makes the tone sound more vintage 50's
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Old 11th April 2006, 02:34 PM   #8
poobah is offline poobah  United States
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You're on the right track Gene. Keep in mind, when these things were done originally the vinyls were often preformed using steam & pressure. Steam is one trick for all of this. If you garage sale... you can cob together a steamer with a hot plate & a pressure cooker... a piece of hose and you're there. A steamer will allow you to pulll wrinkles out by pulling at 45 degree angles to the fabric.

In the case of a long oblong slot, you can actually trace the slot n the backside of the fabric, then makes your cuts and staple/ glue the backside flaps of the hole first. This will leave lots of wrinkles, but steam will easily make them "ease in".

The routing idea is good. Always think about getting cool air in the bottom and having it flow up and across and out the top.

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Old 11th April 2006, 09:25 PM   #9
Trout is offline Trout  United States
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Steam is one trick for all of this

I was thinking,, I Know " UT OHHHHHHHHH"

I can not steam this stuff. It is Treated/Colored and sealed on 1 side, &
#2, Water based contact cement.

The original solvent stuff darn near kills me just opening the can, I am very chemical intolerant due to stupidity as a younger man.
If I can smell the solvent in the air, within 20 minutes I will end up being ILL for days.
I can handle the water based in a well vented garage and high grade chem-mask if needed.

Funny though, solder smoke does not bother me at all ?


One trick I have been using is a sealing iron. The water based contact cement made by dap/weldwood bonds like nails if heated. The heat also seems to soften the coating and allow a fair amount of stretching and pulling around the curves.

I Use This & for the larger flat areas I Use This one

These are carry-overs from my RC aerobatics days. I was a master at iron on film coverings.
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Old 11th April 2006, 10:14 PM   #10
poobah is offline poobah  United States
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hmmm

Time to go get Gunter!

Steam will turn the stuff into total rubber almost...at least along the bias (45 degrees).

I am familiar with those irons... owned a few myself. If you can use those on the fabric without damage that opens the options of using wood glue to attach (as they were done in the first place) the fabric. PVA is pretty harmless stuff and more forgiving than contact cement.

Put a thick coat of white glue on each surface... let dry... then iron on. Yellow glue should thinned about 10% with water.

Worth a try with some scraps???
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