Reverb Tank Problems?

Discussion in 'Amp Tech Center' started by Despres, Mar 3, 2013.

  1. Despres

    Despres Tele-Holic

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    I'm looking for a second opinion of sorts, I recently got a new amp - I won't mention the manufacturer just yet, as I don't want to badmouth him, as I expect him to make this right. The first few times I played it, there were some intermittent sounds I couldn't pinpoint, so yesterday I finally had a chance to mess around with it to pinpoint what is causing the problem.

    It has a long Accutronics tank, which I think the problems are originating from.

    The symptoms:
    1) with the reverb on, the volume drops a bit, and turning the reverb up reduces the volume further.
    2) with the reverb level past about 50%, it gets some strange microphonic sounds.
    3) with the reverb level past about 65-70%, the sound cuts in and out on pick attack.
    4) with the reverb off, there is a very loud mechanical clanging from the head at certain bass frequencies, which goes away when I take the head off the speaker cabinet.

    I am far from an amp expert, but am pretty handy, and it seems to me that 2-4 could all be caused by a loose spring or something inside the reverb tank. Item 1 may or may not be normal - it is a slight drop in volume and I wouldn't have even noticed it if I weren't investigating the reverb in such great detail.

    Do you amp experts think I am on the right track here? I don't want to pull the thing apart before I hear back from the manufacturer on the email I sent yesterday, but I thought I'd bounce my theory off the group.
     
  2. telex76

    telex76 Doctor of Teleocity Ad Free Member

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    Doubt it's a problem with the tank itself. That shouldn't cause amp volume to decrease.
    I'd look at cable connections to the tank first, but it could be anything from pot to tubes to connections on the board.
    Might need more dampening around the tank. Is it in a bag?

    Hard to know anything without knowing what amp make and circuit you have.
     
  3. Despres

    Despres Tele-Holic

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    Thanks for the response. The Amp in question is a Frenzel Super Vibroverb, I'm not sure that helps identify the circuit much, but the reverb is driven by a 12AX7, and I think the circuit is probably pretty similar to an old Fender Vibroverb.

    It is just a head, and the tank is bolted to the front panel of the head - probably has some sort of bumpers in there, but it is not in a bag. It is connected with plugs which appear to be nice and tight. I do have some known good 12AX7s I can swap into it to see if anything changes, if need be.

    I got thinking after I posted the first post this morning, and wondered if my ear would perceive the smoothing of the pick attack caused by the reverb to be a reduction in volume. Like I said, that reduction was just slight, so it could be the effect playing tricks on my ears.

    I have noticed when carrying the head, I can hear the springs rattling more than I've noticed carrying other amps with reverb tanks, but that could be because the other amps have the tank in a bag, too. My thought was if one of the springs in the tank was loose or just dangling there, it could make some weird sounds when the reverb is engaged, and when the reverb gets cranked up, the motion of the spring could cause it to short against the side of the tank momentarily, resulting in the sound cutting out
     
  4. soulman969

    soulman969 Telefied Ad Free Member

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    Just a shot in the dark here but from your description of the head I gather the tank is mounted horizontally correct? Is it possible they used the wrong type of tank and that they used a vertical mount type instead? If there is an identifying model number on that tank you could at least check that possibility out. Can you see a model number and if so what is it?
     
  5. Despres

    Despres Tele-Holic

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    Yeah, it is mounted horizontally, I will check the model number and check that out. I'd like to think that they've done enough of these that they'd know to put the right tank in, but it makes sense to rule out the easy stuff first.
     
  6. soulman969

    soulman969 Telefied Ad Free Member

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    On a custom amp I would think so too but I figured it was an easy enough thing to confirm. All of the Type 9 long 3 spring Accutronics tanks I located are horizontal mount tanks but here's a numbering key just so you an check the specs of that tank. Each number or letter designates one spec.


    Part Numbering for Specifications for Type 8 and Type 9
    Example: 8EB2C1B


    Digit Meaning

    Digit #1 - Reverb Type
    8 Type 8
    9 Type 9

    Digit #2 - Input Impedance
    A 10 Ohm
    B 190 Ohm
    C 240 Ohm
    D 310 Ohm
    E 800 Ohm
    F 1,925 Ohm

    Digit #3 - Output Impedance
    A 600 Ohm
    B 2,575 Ohm
    C 12,000 Ohm

    Digit #4 - Decay Time
    1 Short (1.2 to 2.0s)
    2 Medium (1.75 to 3.0s)
    3 Long (2.75 to 4.0s)

    Digit #5 - Connectors
    A Input Grounded/Output Grounded
    B Input Grounded/Output Insulated
    C Input Insulated/Output Grounded
    D Input Insulated/Output Insulated
    E No Outer Channel

    Digit #6 - Locking Devices
    1 No Lock

    Digit #7 - Mounting Plane

    A Horizontal Open Side Up
    B Horizontal Open Side Down
    C Vertical Connectors Up
    D Vertical Connectors Down
    E On End Input Up
    F On End Output Up
     
  7. Despres

    Despres Tele-Holic

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    Thanks for posting that - my model # is 4AB3C1B, which makes it a type 4 tank, Horizontal/open side down.

    That list there got me questioning whether it is horizontal or vertical - I said it was horizontal because it is wider than tall, but it appears that what I was picturing as vertical would be 'On End.' The tank (according to Accutronics) is 16.75"x4.375"x1.313", and it is mounted so it is 16.75 Wide by 4.375 Tall by 1.313 Deep, I am guessing that is 'vertical', whereas horizontal would be 16.75 Wide x 1.313 Tall and 'On End' would be 16.75 Tall.

    I also noticed that the model number (on a sticker) and the word "Accutronics" are upside down. Since the connectors are on top, and assuming that my line of thinking about horizontal vs vertical is correct, I am wondering if a 4AB3C1C tank would have made more sense for this application.

    Are the springs in a tank loose enough that mounting on it's side could cause problems like I am experiencing?
     
  8. soulman969

    soulman969 Telefied Ad Free Member

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    I'm trying to make certain I'm getting the right visual here and what I'm getting is that the tank isn't mounted to the floor of the head cabinet open side down. That's a proper horizontal mount. Instead it's mounted to the inside front of cabinet head with the open side facing front of the cabinet. Am I visualizing that right?

    If so that may be your problem. I'm not an amp tech but I don't believe that tank was meant to be mounted any other way than open end down and I think you're correct. A "C" mount tank would be the proper one for this application. Open end forward to the inside front of the cabinet connectors up.

    Here's a great tech piece on tanks in general and if you look at the schematics of the "type B" 4AB3C1B and "type C" 4AB3C1C tanks you can see the difference in their orientation.

    http://www.tubesandmore.com/tech_corner/spring_reverb_tanks_explained_and_compared

    This is the Accutronics dealer I just bought a tank from and you can ask them what they think would be correct for your application.

    http://www.tubesandmore.com/

    You can also contact Steve Winkler at this email address. He's the Accutronics rep, a great guy, and a former Ampeg employee. He was very helpful as far as assisting me in finding the right tank for my Roland Blues Cube. He also represents Belton which may also have a tank which is better for your application and any of those tanks can be ordered through their dealer Antique Electronic Supply or Tubes and More. Same place.

    steve@wgiinc.com

    Good luck with your fix. How's the snow situation up in Steamboat. We've been awfully dry down here?
     
  9. Despres

    Despres Tele-Holic

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    Yes, that is the right visual; it is not mounted on the bottom with the open side down, but rather on the front of the cabinet, with the open side facing forward. I am going to ask the manufacturer if he may have put the wrong tank in there - I've been in touch with him, and he is going to work with me (the amp is, after all brand new). I actually think that in addition to a potentially incorrect tank, one of the support springs may have jarred loose during shipping. The problem is proving to be somewhat intermittent, which is annoying, but seems like that could be consistent with one support spring being disconnected - if I move the amp one way, the springs could settle so they short against the metal wall of the tank, and if I move it another way, they might hit the wood wall of the cabinet, or nothing at all.

    Re: Snow - we are probably approaching an average snowpack at this point, although still below average. It has been a strange year though; a typical year here we get a lot of 5" storms and very few 1' or more - this year we have had about a dozen 1'-2' storms and it has just been dry other than that. I was down on the front range a few weekends ago, and it sure looked dry - going through summit county and from the tunnel down to Idaho Springs was even more brown than normal!

    I lived in Englewood a while back myself, right near the Rec Ctr on Oxford.
     
    Last edited: Mar 6, 2013
  10. muchxs

    muchxs Doctor of Teleocity

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    Chances are the tank took a whack in shipping.

    See the part number code for locking / no locking? The locking device keeps the springs from ripping the transducers apart when the amp is transported.

    Non- locking tanks should be blocked with a piece of foam when they're shipped.


    Old Fender amps just have the bag in the bottom. They should be locked down for transport. No one does of course....

    That's why they sell new ones. :rolleyes:
     
  11. Despres

    Despres Tele-Holic

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    When I first had the problems, I looked in the back to see if there was a locking lever that I needed to unlock. One thing that is interesting is in the model numbers list above, they only show a digit for non-locking - since that digit is a 1, I tried searching for the model number with a '0' and a '2' in that place, and no matches were found - Perhaps Accutronics no longer makes locking tanks (at least in the type 4 style)?
     
  12. soulman969

    soulman969 Telefied Ad Free Member

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    Amp manufacturers change tanks periodically and the distributors only stock what's most current. For instance the stock Accutronics OEM tank in my Roland BC60 called for an E mount but it's not available so both the distributor and the Accutronics rep suggested that a comparable D or C mount should work just as well. I just installed the new D mount Marshall type tank today so I'll know whether or not they're right very soon.
     
  13. soulman969

    soulman969 Telefied Ad Free Member

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    OK then I did have the visual correct. Yeah it sounds like he's using the wrong type of tank for that application. The B mount "horizontal" would go on the floor of the head or combo cabinet. The C mount "vertical" would mount on the front of the head or combo cabinet and I'm told it will probably work as an "end mount" in most any amp application.

    Glad to hear he working with you to resolve the problem but it's probably frustrating at the moment. And you could be right. It may have been damaged in shipment as well further adding to your issues. I think a new C mount tank should solve the problem for you.

    Glad to hear your getting some reasonable amounts of snow. We keep hearing down here that the snow pack is far below normal. And you're right it's dry as a bone here. That last storm we had dropped 8"-10" around town and this weekend we're expecting another 8"-10". We can use it. I sure don't want to see another spring and summer like we did last year when half of the Front Range was burning down.

    I'm just a short distance for where you lived here. I'm right next to Englewood HS nearer to Hampden. Small world. Hope you get your reverb issues resolved. Sounds like a dynamite amp. I have a friend with a gorgeous old Vibroverb that does nothing more these days than sit in his studio.
     
  14. Despres

    Despres Tele-Holic

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    Well I've got the tank pulled out and I think Jim's gonna send a different one up here, so I think I'll be back in surf city shortly. He's been very responsive, and really this issue has dragged on more due to my lack of time than anything else. And the amp is pretty awesome, and way nicer than I need, but that's never stopped someone from spending money before!

    The day after I said our snowpack was approaching normal, there was an article in our local paper saying they were going to start watering restrictions early this summer, so I guess it isn't catching up that quickly!

    My inlaws live a bit further down Broadway in Centennial, so we're in that area fairly often - I haven't been able to convince my wife to drop by Arap's Old Gun shop for old time's sake though.
     
  15. soulman969

    soulman969 Telefied Ad Free Member

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    LOL, well maybe next time you're in town you can send me a PM and we can swap some musician's stories and all "shotgun" one or two at Arap's, your bride included. Haha! :D

    Glad to hear you're getting the problem with the amp solved. A tank with the correct mount should solve the problem. I found that a vertical mount can be end mounted just fine but I guess horizontal means horizontal like laying flat on the floor of the amp or the head.
     
  16. Despres

    Despres Tele-Holic

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    Will do.

    For sake of posterity, and in fairness to Jim, I did point out the 'B' vs 'C' mount, and he said they have been using the B tanks in Vertical and Horizontal mounting positions for a long time with no issues - the theory we are operating under is that one of the springs or transducers was damaged in shipping - The lower springs is a lot looser than the upper one (like the upper one is straight across and the lower one sags about 1/4 inch). There are marks on the side of the tank next to that spring, from it hitting the tank, so we're thinking that with the reverb turned up, the motion of the spring is causing it to hit the side of the tank, causing the issues described. Somehow, it must settle next to or away from the metal side of the tank when I move the amp, causing the intermittent nature of the issue.
     
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