Roland JC-77 reverb replacement help

[Mumbet]

I got a Jazz Chorus 77, but the reverb tank died. After doing my research I decided to stick with the short tank, upgraded to 3 springs, so I got a new 8AB2D1A replacement tank. I would have got a MOD brand tank because I've heard good things, but couldn't find the proper model anywhere, so I went with Accutronics. It's supposed to be a direct replacement, mounting open side up on the underside of the chassis.

Anyway, I have some issues installing it. The original tank (marked Hokusei) was attached with just two small screws with plastic sleeves (I assume to dampen vibration), one on each end (in the middle of the short sides of the rectangular tank). The Accutronics tank doesn't have mounting holes on the ends, just the corners. It doesn't even have a rim on the short ends, so I can't just drill matching holes in the tank itself.

I'll have to use a screw on each corner, but I'm not sure if there is room. Has anyone done this replacement themselves, or have any advice for mounting it? Can I drill new holes up into the chassis? Also, the Accutronics didn't come with mounting hardware, and the holes are too large for the old screws anyway (plus I'll need 4 instead of 2)- any tips on proper screws and anti-vibration sleeves or grommets?

I can take some photos if it would help.

Thanks!

 

[ASC67]

Get some suitably sized screws and some rubber grommets or surgical tubing and you should be good to go. Four screws will be more stable than two.

 

[soulman969]

I just replaced one in my BC60 but it's a side mounted tank so it was pretty simple. I guess that's an option you could consider if there's room inside the JC77 cabinet to do it. One three spring short tank is gonna sound like another so if all of the other specs match it's just the mounting plane that varies and there are even some fudge factors with that I was told.

I guess you could also pull the chassis and look to see if drilling into it would hit any of the internal components before having a go at it. If you can do it safely you should be able to make the tank you have work and if not then maybe a side mount or bottom mount option would do it.

 

[Green Lantern]

I replaced the reverb tank in my JC-120 with an Accutronics tank and ran into similar issues. The screw holes were just not lining up. I mounted the tank up there with only two screws and as strange as it sounds, you would be surprised how sturdy that thing stays up there. It doesn't budge at all, even if I molest it. Try getting the screws in there that you can and see how well it sticks.
I've since moved my JC-120 around and everything and haven't had any problems at all.

 

[Mumbet]

Thanks for the responses. I'm going to open it up just to make sure I won't drill into anything, and mount it with all four corners if I can fit it. I'm getting rubber grommets to take care of the mechanical isolation.

 

[taxer]

Dude, I had the exact same issues. Same JC-77, same Acoutronics replacement tank as you. Fit underneath was a bear. You know what I did? I just screwed it onto the bottom of the cabinet. Issue solved. No vibrations, no problems, perfect fit. (Go to Radio Shack and get couplings so you can extend the jacks so they'll reach the bottom of the cab.)

 

[Mumbet]

Yeah, I've been trying to find the best fit and it's frustrating. I opened the amp up, and there's room to screw into the chassis without hitting stuff, but the placement is still tricky, especially with the other metal plates or whatever up there.

taxer- you say you had no issues with the tank being "upside down"? I've read some things that say mounting plane is important, but if it still works I might go the easy way.
Anyone know if mounting vertically on the side will also work?

Just for reference, does anyone know if an amp's reverb circuitry is optimized for a certain mounting plane type of reverb tank, or is it just within the tank itself that orientation matters?

 

[taxer]

taxer- you say you had no issues with the tank being "upside down"?

Mine is not upside down. On my JC-77 the tank is supposed to be mounted upside down under the chasis. Well, my new tank was a bear to get in there, so I simply placed it face down on the bottom of the cab and screwed it in. I don't know if that is upside down or not, it really doesn't matter. No springs are exposed, the tank is tight on the bottom.

And I must say, the reverb is BOOMING. Anthing past 2 and I am in Notre Dame Cathedral. My replacement tank sure is a different animal than the stock Roland Jazz Chorus reverb. I think mounting it solidly down on the bottom against the wood of the cabinet is what makes my reverb BOOM like no other I've heard.

Just screw the thing into the base of the cabinet. That's where most reverb tanks sit anyway.

 

[ASC67]

I believe Reverb tanks are designed specifically for bottom , top or vertical mount.

 

[Mumbet]

I believe Reverb tanks are designed specifically for bottom , top or vertical mount.

That's what I meant. Tanks are made differently depending where they are to be mounted; the 8AB2D1A one I got is meant to mount on the underside of the chassis, just like the original.

So technically putting it on the floor is "upside down", and some things I've read (http://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared) make it sound like that's bad. But if it doesn't really affect the sound who cares. I just wondered if the reverb circuitry in the amp itself is also optimized for the stock type/orientation of reverb tank.

I don't want to order different tank anyway, so I'll be mounting it either on the bottom or side as soon as I get the rubber grommets and extend the wires. Unless someone convinces me it's a bad idea...

 

[Mumbet]

Just in case anyone has the same issue, here's another solution I devised.
I created a plate just large enough for the tank to mount on (with rubber grommets), which is then fastened to the chassis by the 2 screws that held the original tank. That way the tank is in its intended position, and maybe the double isolation is good for vibration dampening too.

I just used a piece of very stiff cardboard to test with, and it works great, no rattles or anything. Going to replace with a piece of thin plywood when I have the chance though, just because I don't trust the screws in cardboard over time.