Dismantling a Porta Flex SB-12 cabinet?

[RobJ]

I want to take my much loved '65 SB-12 apart for a thorough cleaning (I want to get to all the nooks and crannies around the grill cloth) and was wondering if any of our resident Flip Top experts can suggest a procedure on how to do this so I don't damage anything?

While the grill cloth is in decent shape it's filthy, I want to try to clean it but suspect it will need to be replaced.

[nysbob]

Mine looks a lot worse than that, but I'd be afraid of cleaning the mojo out of it.

[RobJ]

Nahhh... mine has mojo to spare.

[Volume4]

Nice!!

I regret selling my SB-12 soooo much

[RobJ]

Ok, I started taking things apart and thought that it would be best to get the new grill cloth before proceeding further. It looks like the speaker needs to be removed before trying to remove the the plywood peice it mounts to. The speaker mounts on one side and the grill cloth on the other. The plywood is about 3/4" thick.

Speaker cone details:



Back of the magnet:




I have no idea if the speaker is original or not, without removing it for a better look I can see no other markings.

Amp section:




Another reason to dismantle the amp is to try to hunt down the source of some pretty annoying buzzes that are most noticable when B or A are played. Any thoughts on what the cause might be?

[JimmyM]

Chasing down rattles is the bane of the Fliptop owner. It could be anything from air leaks to rattling hardware to God knows what.

BTW, I am a fan of replacing old grillcloth but keeping the old grillcloth safely, too. Why? Because you see that crossbar across the speaker? The grillcloth will rattle against it. In the old days, Ampeg used foam rubber to keep the grillcloth from rattling, but over the years it disintegrated. That's why so many original grillcloths on Fliptops look so bad. I can see it's happened to yours. Nowadays, the thing to do is get some black felt and cover all the wood on the front of the grill with it before you put the new cloth on.

[RobJ]

Good information. I did notice there are a few staples through the grill cloth on and near the crossbar. I suppose the previous owner was trying to secure the grill cloth to sooth the buzzing. When applying the felt, how is it attached to the front before installing the grill cloth?

Any comments on the speaker would be appreciated too, as mentioned I have no idea if it's original or not.

[Vintage-Blue]

Originally Posted by RobJ

When applying the felt, how is it attached to the front before installing the grill cloth?

I cut out an oversize piece of felt, allowing about a 1" overhang on all sides. Spread out some old newspaper, lay the felt on it, and spray it with 3M spray adhesive. Don't put it on too heavy or it just gets messy to work with. I then press the baffle onto the felt and cut out the openings and trim the excess using a razor blade. The razor blades work best when they are fresh and sharp and I often end up using two of them on a baffle.

[RobJ]

Hey Mark, thanks for the lesson. I'm also wondering how difficult it is to install new grill cloth. It seems to me it's not a trivial thing with having to make sure the horizontal and vertical lines in the pattern are dead on and the tension has to be just right I would think. Is this the sort of thing best left to a pro?

[beans-on-toast]

The speaker code on the magnet indicates that it was made by CTS in the first week of 1966. Original speaker. The cone looks really black and clean. I'm wondering if the speaker was re-coned. Not a bad thing if it was.

Once the felt is applied, the fun starts. Align the horizontal lines of the grille cloth, centering along the center bar in front of the speaker. You need to staple as tight and as even as you can. This isn't necessary but I use a jig made up of some long clamps with 2 3/4" X 2 3/4" maple newel posts at each end. Kind of like a big vise that holds the grille cloth against the baffle while stapling.

After stapling, you can shrink the cloth with a little heat. With the small size of this baffle, you can pre-heat an oven, open the door and hold it in front. You have to do this carefully as the Ampeg grille cloth is made from a synthetic material and it will melt. It can be done with any heat source. I've used a blow drier but the heat does not get evenly distributed.

When cleaning the tolex, be careful not to use too much water on the edges. The glue can dissolve and lift the tolex.


David

[RobJ]

Ok I'm thinking I should hire this out, the grillle cloth part. I'm not the handiest guy around and will cop to that fact. Thanks for the info David. I'll have to do some looking, hopefully someone around Seattle has the knowledge and experience to do this but I have my doubts.

And thanks for the info on the speaker, for as clean as it is for a speaker that old I suspect you are right that it's been reconed.

[beans-on-toast]

You have to be comfortable doing any kind of work yourself. When you start thinking about it, the work seems harder than it really is. The felt application isn't hard. The grille cloth just takes thinking through and being patient. If it doesn't work, you can take it off and try again. A lot easier than re-tolexing the cab.

There is also the cost of special tools like a heavy duty stapler to consider.

If you do the prep work to minimize cost, any furniture or car upholster can apply the covering for you at a reasonable rate. They know how to do these things.


David

[RobJ]

Thanks, you've been very helpful; as have all who posted here.

[RobJ]

An update and a question; I did find a guy in Seattle with lots of amp restoration experience to install the grille cloth.

Any thoughts on a good replacement speaker? The old CTS farts out pretty easily at fairly low volumes and I was thinking an upgrade may be the solution. Thoughts? I know there are a couple of options at fliptops but thought I'd see if any of you had an opinion on which way to go.

[JimmyM]

My opinion on replacement speakers is do what Fliptops says. Bruce sure called it right using the Beta and Delta 15 for B-15's. I have a 66 CTS 15" and two Delta 15a's, and they sound almost identical to me.

[nysbob]

I've got an EV in mine - it sounds terrific.

[RobJ]

what model EV?

[nysbob]

Originally Posted by RobJ

what model EV?

That I'll have to check. I just know it says "EV" on the dustcap.

[John D]

Originally Posted by nysbob

That I'll have to check. I just know it says "EV" on the dustcap.

I went with the Beta 12 in my SB12. Remember to break the speaker in. I didn't, and it didn't sound very good at first; weak in the low end. After a few months of light playing, the bottom end has opened up nicely and it sounds great.

[RobJ]

Good input, thanks John and Jimmy.