Ventilation Advice on Small Cab 2204

[bcmatt]

I guess I am trying to balance good function with aesthetics...
So, I have a JCM800 2204 that I built a few years ago, and I love the cabinet that I had my dad build for me. A very classy feeling black vinyl covering with white piping and Purpleheart strip on the front valence.
[IMG1200]http://i49.tinypic.com/ju8ug9.jpg[/img]
It's a nice compact cabinet, but that has it's drawbacks... well one drawback: The heat will build up in the cab too easily unless I keep that back off.
[IMG:640:480]http://i55.tinypic.com/291ol8y.jpg[/img]
But, I like the look of the back and the idea that it will protect the glass, so it would be nice to engineer a good way to get some better ventilation in there. Here is a pic of the inside of the cab.
[IMG:640:480]http://i51.tinypic.com/2zqdc49.jpg[/img]
I have a couple 120VAC fans now, and you can see it resting on the left side of the chassis (unmounted).
I also have a single 12VDC computer fan currently installed in another amp that I could yank for this one (since I think I'll give it a bigger AC one).

As you can see, things are quite tight in there, and there is no room anywhere remotely close to the power tubes for the AC Fan. I could probably squeeze the little DC fan between the Power tubes and OT, but it would be tight, and I would wonder if that would be too close to the power tubes...

Is it pointless to try and put a fan in there? Would I be better off trying to install a vent on top? I could cut a strip of this metal and spray it gold and mount it on the top of the amp towards the back:
[IMG:640:480]http://i51.tinypic.com/aa7uio.jpg[/img]
But really, I'd worry about really getting it to look good. How would I even cut metal to look good in a top-mount type situation. I don't even know what you use to cut metal in nice straight finished lines. What sort of tool do I need a friend to have for that?

Can anyone think of perhaps another vent-like item that would look good on top?
I thought of mounting the AC Fan right into the top of the cub under the handle, but realize there is no way to do it tidily without at least a nice looking vent with it.

Any good suggestions?
The AC fans seem VERY silent running. (much quieter than the 12VDC) but I wonder if it would cause noise being so near other amp components. Anyone mounted AC fans in amps?

Anyone have any other aesthetically pleasing solutions?

[ToneMerc]

Considering that the enclousure is sealed up pretty tight just sitting a fan inside won't do much good, you need to get cool air in, warm air out. In the perfect world the top would be vented across and a cool air intake fan would be mounted on the inside of the enclosure wall drawing in cool air, while letting the warmer air escape through the top.

One option might be to install a Vox AC30 vent across the top, that in itself might be enough to allow warm air to escape while allowing the back to remain on.

I would suggest picking up a cheap IR temperature gun to aid you.

TM

[bcmatt]

Thanks Tonemerc!

Ya, I guess this guy shouldn't look too bad, even if it is plastic:
http://www.tubesandmore.com/scripts/fox ... tem=P-H211
[img:500:88]http://www.tubesandmore.com/cemirror/inv/P-H211.GIF[/img]
There's a chance that the 3" width is too much to fit between the handle and the rear; I'll have to measure.

While $6 ain't bad, it would be a while before I filled up the order enough to make the shipping reasonable. Do you ever see these things in local guitar stores?

[Structo]

I'd be more tempted to use this Marshall style vent material.

http://www.tubesandmore.com/scripts/fox ... tem=P-H210

What you would do is carefully measure about four times then cut a slot in the top rear of the cab.

I would cut the tolex with a razor knife so that I could glue it to the sides of the cutout when done.

Then staple the vent material from the underside.

I saw one cab where the builder put a fan in the bottom of the cab.

But the chassis would have to have room for it and also some way for the air to circulate throughout it.

[bcmatt]

I'd be more tempted to use this Marshall style vent material.

http://www.tubesandmore.com/scripts/fox ... tem=P-H210

What you would do is carefully measure about four times then cut a slot in the top rear of the cab.

I would cut the tolex with a razor knife so that I could glue it to the sides of the cutout when done.

Then staple the vent material from the underside.

I saw one cab where the builder put a fan in the bottom of the cab.

But the chassis would have to have room for it and also some way for the air to circulate throughout it.

I could never fit a fan inside the chassis.

But you are right that the gold metal grill would match the best. We did that back piece exactly like you describe:
[IMG:640:480]http://i55.tinypic.com/291ol8y.jpg[/img]
I'm not sure if we have any remaining pieces big enough. (It was actually an old piece of satellite dish mesh we found and spray-painted gold). Sure beats the ridiculous prices that the original marshal stuff costs.
My dad continually complained about what he calls "inside corners" when tolexing, and I am afraid of the process of cutting the vinyl and peeling it back, and then having enough to fold into the thickness of the plywood.
It is possible and it would match the back the best, so I am still considering it, if I can find the right mesh.

Despite being easier in the tolexing side of things, a grill that could attach from the top could also leave potential space for mounting a fan from the inside that sucks air out that top vent. The clearance above the power tubes has got to be under an inch...

I wonder how ugly the amp would look with a fan vent like your picture, but on the top of the cab behind the handle...

[bcmatt]

How would you go about cutting this piece of metal?
A 1cm perimeter around the outside of one of those rows of slits would make a nice looking top-mounted grill if I painted it gold I think:
[IMG:640:480]http://i51.tinypic.com/aa7uio.jpg[/img]

I know some welders. Do they have ways of cutting metal straight or is everything they do free-hand and messy?

[dynaman]

Is the amp actually suffering from issues related to heat? Cab covering doing funny stuff? Trannys dripping varnish?

That's a pretty big vent on the back panel and I personally wouldn't worry about it but you could just ditch the back panel in favor of a big old piece of ventilated metal.

50W smallbox Marshall heads had no more ventilation than your own present setup.

[bcmatt]

Is the amp actually suffering from issues related to heat? Cab covering doing funny stuff? Trannys dripping varnish?

That's a pretty big vent on the back panel and I personally wouldn't worry about it but you could just ditch the back panel in favor of a big old piece of ventilated metal.

50W smallbox Marshall heads had no more ventilation than your own present setup.

Yes, when I did leave the back on, I do feel like it was having heat related issues. The covering is Marine Vinyl and it was applied with contact cement. The vinyl lifts right away from the wood near the tubes. (we know to use more amp-appropriate materials now).

Air was not getting out. Pictures make this amp look deceivingly typical for a small box marshall, but believe me, it is well undersized. It is at least and inch or two shorter and the fact that the back vent does not go to the top of the back somehow causes significantly more heat build-up in the more confined space. The power tubes reach about a mm higher than the top of the vent reaches in altitude. I really haven't risked playing with the back on in a few years. It scares me too much. Despite being poorly designed, I do like the look of the back and it was well built.
Whatever heat ventilating system I end up using will have to look just as good, otherwise I might as well just keep leaving the back off, which seems like a waste of the back.

My motivation for this is partly because I am thinking I should sell the amp. My Liverpool made this guy quite obsolete for my needs and I am running quite low on life savings and food money. I got a nicely working PPIMV on it now, and it would be nice to not have to tell potential buyers that they should avoid leaving the back on when they play. The simplest things turn people off.

[dynaman]

Extend the existing opening to the top of the cab or simply cut off the top half off the back panel. Leave enough vinyl to properly wrap any new edges.

Or just install a fan if that's what you really want to do.

[bcmatt]

Extend the existing opening to the top of the cab or simply cut off the top half off the back panel. Leave enough vinyl to properly wrap any new edges.

Or just install a fan if that's what you really want to do.

I suppose you are right. It would be a lot easier to butcher that back just slightly than to mess with the rest of the cab. That grill would not be big enough, but at least any new material doesn't have to match it anymore.

It wouldn't take much to open up that top oval into a giant Letter H like most Marshall backs.

I think you caught me. I do seem to want to install a fan. Perhaps I should do that first if I can find a place to fit one. And then step two would be to alter that back piece when the fan doesn't seem to help enough.

[overtone]

not sure if there is a heat issue here, or just a concern, so a quick risk-check would be informative:
you could measure the temperature involved against what the vinyl covering is rated for.
Curling Tolex is common. A staple-gun can sometimes help.

Before you start cutting, take a moment to reflect on:
1. the flow of heat
2. how the principles of effective ventilation state that there must be a way in and a way out for the air
3. keeping the entry and exit apart will help prevent a recirculation.

Best, tony

[Jana]

Maybe just leave the back off when gigging. Put the back on when it's picture time. There's a reason why a lot of older marshalls are missing the back cover!

[Structo]

True that, I leave the back off of my 100w Dumble.

Another issue with those cabs is there is no opening on the front valance of the cab, those at least allow some circulation from convection.

If you want a vent then the easiest would be the black plastic vent from AES that you posted.

It will conceal the cut in the wood you have to make.

Or, build or have built a larger cab with flow through ventilation.