FINALLY FINISHED closing my F-30 combo's open back!!

[MusicManJP6]

I would like to enclose the back of my F-30 combo to get some more bass response out of it. I thought about using some 1/2" plywood and covering it with black taurus tolex if I like the sound of it. I would not attach it with screws but rather try to make it a snug fit so I can still keep the power cord, footswitch, and footswitch cable in the back.

I have two options:

Red: cover from the top of the existing back piece to the bottom of the chassis support (i guess that's what the metal plate across the back is for).

Green: take the chassis support off and cover the whole area.

See pic for clarification:

Any opinions?

 

[nemesys]

I don't know for sure, but it seems like it could possibly overheat and get damaged or start a fire if you close the tubes in like that. I think the manual warns to leave some space behind the amp when playing it for this reason. I guess you might be okay with your first option, going to the bottom of the metal plate (I think that's just a guard to protect your tubes, I don't think it's load-bearing).

 

[sixtonoize]

Honestly, I don't think that you'll get what you're looking for from the solutions that you've proposed. Completely closing in the back of the cab will cause serious cooling issues, as previously mentioned, and leaving a substantial amount of the cab open won't really improve your bass response. I think that the best option for you is to pick up a sealed 1x12 speaker. It certainly won't be as cheap as wedging a piece of wood in the back, but it's the only way to really get the bass response of a sealed cab.

 

[MusicManJP6]

I thought about grabbing a thiele to add to the setup, but was hoping to be able to keep the portability factor of the combo and just add a bit more bottom end by enclosing more of the back...

What about enclosing this much? (see blue):

It will still have as much ventilation above the piece as it currently does. Heat rises after all, so closing below the top blue mark wouldn't seem to be much different. I'm going to try to cut some test pieces this weekend and see how it sounds. It may not change much or just sound bad in general... I'll update when I test some with it...

 

[Charlie]

You might damage the amp and you are definitely going to de-value it by doing this.

I wouldn't do it if I were you.

I'd look into getting an extension cab or maybe trade it in for an Ace.

 

[sixtonoize]

It will still have as much ventilation above the piece as it currently does. Heat rises after all, so closing below the top blue mark wouldn't seem to be much different. I'm going to try to cut some test pieces this weekend and see how it sounds. It may not change much or just sound bad in general... I'll update when I test some with it...

Heat DOES rise...but it can't just leave. If you enclose the back up to the blue area, you'll provide enough area for the heat to escape, but not enough area for cool air to replace it. If you don't leave a path for the cool air to replace the hot air, you might as well just seal the whole thing off.

 

[MusicManJP6]

gotcha. OK, one last idea to throw out there and then i'll give up.

What if I enclose the area indicated in red but remove the tube protector bar?

Also, I am hoping I can velcro this piece in instead of screw it in so I can take it on/off and still store the footswitch, footswitch cable, and power cord in the back for easy transport. I would think this would not harm the resale value since it is reversible.

Thanks for the responses so far...

 

[Alivefor5]

Why don't you mimic the shape of the 3/4 back cab? I know you used to have one with your Roadster head. It would have a rectangular hole around the speaker magnet and plenty of opening at the top for cooling air to circulate. It wouldn't be a closed back but might offer some of the advantages of both open and closed. I'm obviously a big fan of the 3/4 back cabs myself.

 

[MusicManJP6]

Actually, I have thought about that as well! BUT, I would need the dimensions of the cab as I sold mine with my Roadster. I would basically need all measurements so I can keep everything in proportion when shrinking it down to the size of the combo. So, that means the width and height of the cab, the height of the bottom and top of the hole at the speaker magnet (and width of the hole), and the top of the back piece, the width of the lower cut of the piece at the top that is kind of lower (and the height there), and the width of the top cut. This is all kind of hard to explain. Maybe I should grab a pic of the back from Mesa site and do some architectural type dimension drawings of what I need measurements for... More to come later...

 

[Alivefor5]

Here ya go, dimentions from my 3/4 back 1x12 cab: (all in inches)
outside dimentions of the cab: 26 1/4 x 19 1/2.
rectangular hole: 2 1/4 x 9 3/4.
hole centered 5 1/4 from bottom edge of cab.
top of back piece is 15 1/2 from bottom edge of cab.
each end of top is 3 3/4 from side edge of cab.
lower part of top cutout is 16 wide and 13 3/4 from bottom edge of cab.

Since you've owned one this should make sense. Might be Greek to other folks though.

 

[MusicManJP6]

WOW! Thanks man! That makes complete sense for sure. I'll see how that will work out. I found a piece of wood I had laying around that was as tall as the bottom of the amp to the bottom of the tube protector and just layed it up against the back of the amp for a few minutes and it made a noticeable difference! The bass sounded 'harder' and more defined. If I can get a good mix between closing the back and leaving room for air flow, I think it will work. I'll work up a template from the dimensions you sent over and superimpose it on the pic of the back of the F-30 to see how much room it will leave for air flow... I'll post the result.

Thanks again Alivefor5!

 

[phyrexia]

That's a V30 in that amp, right? Get rid of it. A tighter sounding speaker might work in there better. EV maybe?

 

[MusicManJP6]

Actually, I swapped the stock V30 for a C90 that used to be in my 3/4 back (before I sold it). The swap made a difference in itself.

So here's the latest in the development of a safe and effective method of closing the back of the amp some:

Pretty self explanatory - the top of the new back piece is going to be at the top of the tube protector even though the pic overlay is a little off. I'm going to try to get the new piece cut today! It will be held in via velcro like planned once I cover it in tolex. But i'll stick it in there and lean something against it to see how it sounds for now. If all is well i'll order some tolex...

Now what do you all think?

 

[madryan]

The thing you're forgetting is that EL-84 tubes and "Bass Response" don't really go together, at least in my experience. I tried a buddies F-30 through my sealed back 212 and it still didn't "Chunk" like any of the 6L6 amps I've owned would.

If you're dead set on a sealed back then do it right, and buy or build a headshell, or at least unplug the regular speaker and run that thing into a sealed back cab. That's the only way you're going to see a significant change. Anything else will just bugger up your amp.

 

[MusicManJP6]

I know what you mean Ryan. I'm just trying to squeeze every last drop of usable bass out of the combo while keeping it portable. I don't expect it sound like a thiele cab. I just know that there is a bit tighter bass to be had - this was obvious when I covered the back briefly with a piece of wood below the tube protector bar...

 

[sixtonoize]

Looks good!

 

[212Mavguy]

Hey Music Man,

I like your thinking...a lot. I did some messing around with a Peavey Mace 2/12 cabinet, the amp got got left in the weather by the previous owner so I junked the non operating speakers and chassis. I made a semi closed back 2/12 using some 3/4" thick maple from some chopped up cabinet doors, leaving a slot about 3 1/2 inches all the way across the back in line with the magnet centers, used the skinny bottom stock back baffle to block the chassis front slot, and stuck a pair of very very rare JBL g125's in it. That cab is amazing, loud, warm and full in its sound. As far as hurting resale value, I don't think a couple of extra holes is gonna hurt, that's all that would show to some very nitpicking eyes when you remove your added piece. I think that the shape of the added piece shown in your most recent illustration is going to work very well for both sound and air convection currents for power tube cooling. I do agree with the post about using evm 12l. That speaker along with your back mod would allow you to turn down the bass knob a fair amount, that will allow more harmonics to come through from the mids and top. It is a superior build and sounding speaker to the Celestion c90, IMHO, and that Celestion is no slouch. Then it will be time to do some NOS tube rolling... :wink: No need for tolex, nobody is gonna see the back of the amp anyway. Some flat black canned spray paint will do just fine. Best of luck!

 

[MusicManJP6]

Hey thanks Mavguy. I feel pretty good about the new piece for the back too. I am going to try my luck with velcro so I can take the piece on/off for storage. If that proves harder than it seems to make work, then i'll use the existing two screw holes from the tube protector bar and maybe two more down lower. As for tubes - I just installed a JJ retube kit and it sounds INCREDIBLE!!! I highly recommend JJ's.

I used to own a C90 loaded thiele and an EV loaded thiele. Both speakers are great, and extremely similar. The EV is more transparent but weighs a good 8 - 10 pounds more. In vein of keeping the combo portable, I think i'll stick with the C90 for now. I'm happy with the tone of it.

I'm going to try my best to get this thing cut today! My brother may be able to help me out if he has time. Mavguy might be right about painting it flat black, but how much cooler would it look if it matched the rest of the cab?!

More to come later...

 

[sixtonoize]

I think that if it's done well, having a matching back panel could actually IMPORVE the resale value of your F-30. I'd definitely pay more for a matching custom piece to improve the tone. IMO, it'd be totally worth it to spend the extra time/cash to get it tolexed (in addition to looking badass).

But you gotta post pics when you're done.

 

[MusicManJP6]

I'll definitely post pics. My brother and dad are busy today so i'll have to cut the piece this week sometime...