Reverb tanks?

[Phil_S]

Much to my dismay, I just found out that Accutronics and Belton are the same company, in Korea. What prompted the discovery is the thought that I might try for my next project a head with both reverb and tremolo. I have an old Gibson reverb transformer and thought I might order one to mate to it. They will sell me the tank for $20 and then charge me $25 to ship it. I need a 4FB2A1B. Is there any other way to do this?

[Firestorm]

Hi Phill,

Are you sure about the tank number? I've never seen an F tank used in a transformer-driven application. I thought most Gibsons used type B tanks (150 ohms). No matter, AES seems to have A, B, E and F type tanks (all with 2,250 outputs). The rest of the specs (insulation and mounting) you can alter yourself, so there must be something you can use.

[Milkmansound]

$25 to ship seems insane - I am sure you can do better than that on ebay or from mojotone or somewhere like that

[Phil_S]

Hi Phil,
Are you sure about the tank number? I've never seen an F tank used...

This is an example of a project set aside for a long time. In October 2008 I exchanged email with someone from Accutronics when it was still USA owned. Fortunately, I saved the email. I guess they had archived every application that Gibbs provided tanks for because he replied very quickly with the tank number. This was for a GA15-RVT, which was made in the early 60's. He says his notes reference the Gibbs model C, which is the "same as an Accutronics model 4FB2A1B."

Apparently, the transformer I've got needs the F tank, input 1475 ohms. I think this may be the standard that Ampeg was using, too.

It is curious, I contacted the current Korean Accutronics organization directly and they provided pricing and payment details. Then I contacted the USA distributor, who, in an odd kind of way, cautioned against buying substandard Chinese copies of the Accutronics tank but the information on an actual purchase was not that helpful. There are also some murky details about whether the Belton equivalent (same Korean company also bought Belton) is the same thing or different.

Meanwhile, some searching on the internet took me to one forum where they seemed to really like the MOD reverb tanks. It was skimpy on details, but at least a couple of people seemed to think the MOD tank was better hardware and more faithful to the original design. I sent email to see if I can get the actual tank I'm looking for. They have readily available the long decay model (4th position = 3), where I'm looking for the medium decay (4th position - 2).

I am hopeful maybe it isn't a big deal, medium vs. long. Maybe I just buy the one with the long decay? I don't know much about reverb tanks. What determines delay? Can this be easily modified by the end user? I'm hoping maybe it is the type of spring used, in which case, changing the decay shouldn't be difficult to obtain. The MOD tank is only $18 and domestic shipping is considerably less than $25, which is silly even for Korea.

[Jana]

What determines the long delay?

Ground shipping!

Seriously, I have tinkered around with reverb tanks and from what I can determine, it is the springs that determine the delay. The long delay tanks have much looser springs in them and are more "boingy." The long delay tanks are also more susceptible to spring slap if the the tank is jarred. I had a 3 spring, long delay tank that I wanted to shorten the delay a bit. I wanted more delay than a medium but less than what the long provided. I carefully snipped and shortened the springs a little bit to tighten them up. This worked and I created a delay that was between the medium and the long. After that experience, I think I am ready to try brain surgery (I'm already good with a soldering iron, what more is there to know?)!

[M Fowler]

Jana,

I know some politicians that are in need of a lobotomy.

I'll drive them over to you!

Mark

[Firestorm]

The Antique Electronics Supply website shows a NOS Kustom reverb tank numbered R4FB2C1A. NOS so it's likely a proper Accutronics; it has your 1,475 input and medium decay. What's different between that and what you specified is the Kustom one has both input and output grounded (it probably has the old RCA phenolic jacks so you can defeat the ground on one fairly easily) and it was designed to be mounted open side up, which should be perfect in a non-Fender head (tubes up).

As you know, a reverb head needs to be taller than usual to put some distance between the power transformer and the reverb transducers.

[Phil_S]

Firestorm: AES is a great find. So many places to look, so thanks for the lead. I see the Kustom tanks and they have the right numbers. I agree, C in the 5th position = input insulated/output grounded, shouldn't be a problem to work with.

The "A" orientation, open side up is probably even better for a head. I was going to get to it, but now that you opened up the matter, just how much space should there be between the tubes (pointing up) and the tank, hanging from the roof? I was thinking that I'd probably cut a dado in the sides of the cabinet wall to make a shelf/box that I could foil line to isolate it from the amp. Is that overkill?

BTW, I see that AES also has fairly reasonable prices for bags, too. I was thinking I'd make one, but for $11, it almost isn't worth the effort.

--Phil

[Phil_S]

I have tinkered around with reverb...I carefully snipped and shortened the springs a little bit to tighten them up. This worked and I created a delay that was between the medium and the long.

Jana, any idea of how many turns you removed from the springs?

[LeftyStrat]

I remember reading somewhere you could change the length characteristics by simply attaching a rubber band between the different springs, say one third from the end of one spring to one third the end of the other spring.

Also, I just received a couple of the MOD reverb tanks, and the quality looks good. I haven't hooked them up for a listen yet.

[Firestorm]

just how much space should there be between the tubes (pointing up) and the tank, hanging from the roof? I was thinking that I'd probably cut a dado in the sides of the cabinet wall to make a shelf/box that I could foil line to isolate it from the amp. Is that overkill?

Fender's Dual Showman Reverb head is 13" tall, versus 8.25" for the non-reverb version, so figure you need at least 5". As to boxing and shielding the tank: well, you can't use aluminum foil for this because it won't block the field from the PT which what you'd need to do. As someone pointed out here recently, mu metal is good at this, but not cheap. As long as one the jacks is grounded, the tank itself becomes a shield, but you should also shield the open side of the tank -- with steel -- to close it off. Of course, the best shield against EM interference is distance, so you want to get the output side of the tank, in particular, as far from the PT as you can.

[M Fowler]

I know you guys know your stuff but I build a Rocket Reverb running 6550 tubes into a Dr Z Route 66 blemish head cab. Not much room but this amp has no noise, hum or buzz. Nothing but sweet subtle reverb.

Mark

[Firestorm]

That's cool. You do have the sensitive end of the tank pretty far from the PT. And I think there's a lesson there about transformer orientation, as well. Having a good PT helps, too.

[soma_hero]

I built a deluxe with one tube reverb. MOD long delay tank, long spring tank, dont recall the impedance, drove it with a fender reverb tranny.

I made a tight squeeze cab with the tank screwed in on the back of the head face plate. Chassis mounted literally right behind the tank with the tubes not far from the tank. No noise to speak of.

I've used a number of MOD tanks and they're great. I've never built one with an Accutronics so i actually can't compare, but we're building reverb circuits here. Deliberately buggering up the sound, so how can you compare sonically? If the impedances are a match I don't see much difference...

[Jana]

"Jana, any idea of how many turns you removed from the springs?"

No, it's been a while and my brain is a bit fuzzy. I think it was about a half inch of spring length. I did it in short increments of about 1/8 inch at a time until I got the desired results. This was a 3 spring tank and as I recall, the three springs weren't exactly the same to start with--each seemed to be slightly different with tension. Maybe this was done on purpose to widen the range? I don't know.