Reference Post - Accutronics Reverb Tanks

[Default]

There's a lot of good information on the Accutronics website. Here is a link to the solid state reverb schematics section. Codes are also available on the rest of the site.

 

[capnjuan]

Good stuff Steve; always in the fog trying to ID tanks ...

 

[matsickma]

Does anyone have a reliable cross reference for Gibbs to Accutronics reverb pans?

M

 

[Guildmark]

I might!




Uhh.hh.h...
What is a cross-reference for a Gibbs to Accutronics reverb pan?

 

[Default]

Accutronics used to be Hammond of organ fame.

Gibbs was started by some Hammond employees and became a successful competitor.

Later, Gibbs was bought by Hammond.

Hammond became Accutronics.

Sound familiar? :wink:

 

[capnjuan]

I might! Uhh.hh.h... What is a cross-reference for a Gibbs to Accutronics reverb pan?

Well ... it's something that doesn't exist. The typical Gibbs reverb can has a paper label in it saying "I'm a Gibbs can" but, except for two-, and sometimes 4-place ID#s stamped on the top, nothing about the can's electrical characteristics; input/output impedance particularly and although very polite, Accutronics is of little help matching original reverb can #s with their own products.

My speculation is that they've been burned too many times guessing at what might work; you can send them schematics and they still won't take a stab at it. If they ship, you install and you no like the sound, the buyer's conclusion is that it's the wrong can, ship it back to Accutronics ... they no want it back ... on and on. I tried to match old Gibbs #s v. new Accutronics #s/can in Coastie's T1 RVT; Accutronics' attitude was 'just tell us what you want'...Coastie's new can is a best-guess substitute. The problem is compounded by people's varying appreciation of reverb; some say if it's not 'rain forest' then no good ... others want it drier and if too wet ....... but if you find a cross-reference, let me know!

 

[jp]

Thanks for posting that, Steve. Very timely--I've been thinking of replacing the 3-spring, medium delay tank on my Mesa DC-5 with the long delay--only difference is an insulated input instead of a grounded input. I don't know if it's the circuit design or what (sorry Randall), but the reverb has always been pretty weak. This Mesa series is famous for it. I got a few tips after doing a little chatting on a Mesa BB. Advice was to try higher gain preamp tubes like the Chinese GT-12AX7-C or the JJ ECC83S for the reverb to help drive the current through the complex front ends of a Mesa.

 

[capnjuan]

... Advice was to try higher gain preamp tubes like the Chinese GT-12AX7-C or the JJ ECC83S for the reverb to help drive the current through the complex front ends of a Mesa.

Hi JP; hope the increased gain works for you .... some of the common 'web-wisdom' for fixing noisy reverb includes reducing the gain by subbing in 12A U/T/Ys for 12AX7s but maybe this is better applied to older, less well-engineered gear. Is there a public domain schematic for Mesa DC-5? Alternatively, do you have a hard-copy you can scan and email? Cheers cj

 

[jp]

Hi capn,
Thanks for your concern. Here's one (13 pp) at Schematic Heaven. There are two versions, thus the DC-5 and DC-5B. Mine is the first, DC-5. You'll notice the schematic sometimes shows DC-5B. That's because they share some circuitry and differ in the FX loop/Reverb. I like how they also show the block diagram, for the different sections of the amp as well.

. . . only difference is an insulated input instead of a grounded input.

Do you think this will make a difference? I'm wondering if I understand properly what this means in regards to a reverb tank. Would the wiring be any different? I think I'd just plug it in. Not sure until I get into the guts. OEM tank in my Boogie is the P-R9AB2A1B, Type 9 medium delay. I was thinking of trying a P-R9AB3C1B, with the longer delay.

 

[capnjuan]

Yikes JP; adults have amps like the Mesa DC5 :shock: Reverb loop shown below, one channel only ..... sorry for the poor resolution; image went from Adobe to PowerPoint to Paint and up to the web ....

Sure, try switching out V5 but don't forget V3 and V4 that are the sources of the signal; if they're not working very well, the reverb circuit and V5 don't have a chance. If you have the amp open, good time for housekeeping. Don't forget to spray/clean the new-in tube pins and the sockets; could have some corrosion. If no change, this amp has two volume controls; one is the source of the to-the-reverb signal and the Master to which the signal returns; could be that either/both are dirty. Finally and depending on much of this you want to mess with, you might want to meter the reverb supply voltages; points B & D on the power supply and at the plates of V5; 416V and 118V respectively.

I note that the in/out of the reverb circuit are controlled by Relays RY3a and RY2b. The power side of the relay is easy; it either works or it doesn't but the signal side ... you can't really open the relay and clean the contacts - you can't do anything but replace it. Every time it's switched, a little bit of one contact is burned from one side to the other; like a power switch on an amp. Over time, the contacts slowly burn up and if the switch fails 'open' it won't do anything. If it fails closed, then must plug/unplug cord to turn amp on. In the meantime, a layer of corrosion forms on the contacts impeding/degrading the signal. My point is that the contacts inside the relay are a potential source of signal grief the fix for which does not come in a spray can (make that a maintenance man's much-beloved spray can :wink: ). If Mr. Mesa wanted to make nice-nice with downstream techs, the relays would be easy to pop in and out of sockets soldered to a pc board ... in which case ...

Insulated v. Grounded input; in the pic above the secondary side of the reverb transformer has one leg tied to the can/springs and the other leg directly to ground. On the output side, there is a shielded cable with the shield grounded, as is typical, at one end only. I interpret the drawing to show 'insulated' input; essentially one leg carrying the signal. In the more common scheme, the reverb can itself is the ground conductor and with either 1/4" or RCA jacks, the ground is continuous from the input, through the can, and out to wherever it goes. I think the goal in the design is noise control and eliminating yet another potential source of ground loop hum; unless you have reason to think there's something wrong with the wiring itself, I'm not sure I'd mess with it.

T'were me, I'd do the housekeeping and tube-rolling - it takes longer to write about it than it does to do it and I'd have a peek at how those relays are seated - before I switched out the can. Because I am immature and petty, I'd be pretty upset if I went out of pocket $50-odd only to find that the new can didn't make any difference at all .... :evil: :evil: :evil: ....... CJ

 

[jp]

Wow! An enlightening diagnosis, Dr. Juan. It sounds like pretty basic maintenance and well within my technical limitations.

Yikes JP; adults have amps like the Mesa DC5 :shock:

Yup. I just fill it up with gas and drive it. Most of the newer MBs make this look like a Victrola next to an iPod. Goes against the major claim by every amp builder in Hunter's book, "Simplicty is best." Seriously, this amp has been hauled around from outdoor shows to dirty clubs to college dives, as well as containered overseas a few times. Although I'm used to going through a fair share of contact cleaner, I may have start buying at Costco.

It is time for a thorough going over, and I may do it all at once.

I note that the in/out of the reverb circuit are controlled by Relays RY3a and RY2b. . . . Over time, the contacts slowly burn up and if the switch fails 'open' it won't do anything. If it fails closed, then must plug/unplug cord to turn amp on. In the meantime, a layer of corrosion forms on the contacts impeding/degrading the signal.

You may have hit on it, capn. If one of these relays fails, though, will any reverb be coming out at all? I do recall the signal being a lot more wet.

I interpret the drawing to show 'insulated' input; essentially one leg carrying the signal. . . . I'm not sure I'd mess with it.

Interestingly enough, the current tank is a grounded input, and the one I'm looking to replace it with is insulated.

Thanks for the analysis Professor! Always value your technical expertise.
jp

 

[capnjuan]

If one of these relays fails, though, will any reverb be coming out at all? I do recall the signal being a lot more wet.

There are two sides to a relay; a coil/slug side and set of contacts. If one of the two relays fails in the open position defeating signal, no reverb at all. Degraded or pitted contacts probably would be noisy / buzzy / scratchy but wouldn't necessarily influence depth or wetness. But if your 'Depth' control is nasty or out of tolerance (too little/much resistance to ground), that would make a difference.

Interestingly enough, the current tank is a grounded input, and the one I'm looking to replace it with is insulated.

"Lucky is the owner/tech who finds 1:1 correlation between what's on the schematic and what's in front of them" St Leo of Fenderia

Good luck; let me know if I can help; also love gut-shots if you get the time. CJ

 

[jp]

There are two sides to a relay; a coil/slug side and set of contacts. If one of the two relays fails in the open position defeating signal, no reverb at all. Degraded or pitted contacts probably would be noisy / buzzy / scratchy but wouldn't necessarily influence depth or wetness. But if your 'Depth' control is nasty or out of tolerance (too little/much resistance to ground), that would make a difference.

That's what I thought--dead relay, no reverb. There is reverb, but very faint. We'll see what a little Deoxit party inside reveals.