valve reverb questions

[HTH]

Hi all,

I'm rebuilding a 2210 Marshall that I've had for a while and never really got on with and am planning on having reverb on this amp (first time putting reverb in an amp, so I've got questions that I'd appreciate some views on)...

The typical Fender reverb uses a 12AT7 in parallel and half of a 12AX7 gain stage.

I've only got two triodes (or a single 9-pin base) to play with, so I was thinking of the following ideas...

* single 12AT7 triode driving reverb transformer @ 22k
* single gain stage after reverb tray replacing normal 12AX7 stage (slight drop in gain though)

* ECL86 with the pentode side driving the reverb transformer, plate resistance is 48k though
* triode side is very close to 12AX7, so that would replace the normal gain stage after the reverb tray

The perfect situation would be a 9-pin valve that is half of a 12AX7 and half of a 12AT7, but I'm not aware of such a beast.

Any ideas and suggestions welcome, just trying to think this one out before ordering the reverb tray. Already got an OT with a 20k-23k (tapped) primary and 4/8/16 secondary.

Cheers!!!

[HTH]

also, in practice, does it make any difference if you mount the reverb tray open side up or down? - this is to go in a head, so the open side would be up, however trying to find a reverb tray for sale designed for open side up installation is proving very tough - they're all open side down for combos.

[g1]

The perfect situation would be a 9-pin valve that is half of a 12AX7 and half of a 12AT7, but I'm not aware of such a beast.

There is a tube that is half 12AX7, half 12AU7 if that will work for you.
12DW7 AKA ECC832, now also available with sections reversed ECC823.
http://music-electronics-forum.com/t92/

[Sock Puppet]

There's a load of info in this PDF regarding orientation and one of the tanks (4FB2B1A) at hot rox is centred for open side up... out of stock though. You could easily screen off the open side of a bottom mounting one and use long bolts to fasten it to the top of the head.

http://www.electricalfun.com/workben...everb_tank.pdf

[52 Bill]

Mesa used a single 12AX7 for drive and return on a number of their amps. Unless you expect to get stand alone type reverb results, a simple system will suffice.

As for tank mounting, there really isn't that much difference in modern tank construction to be overly concerned with it. It is far more important that the output side of the tank be mounted as far away from the power transformer as possible.

[Jazz P Bass]

For whatever technical reason, Accutronics always had an 'orientation letter' in there code.
As far as open side down or up, I think it is the way the springs are mounted.
You don't want the tray hitting the pan.

[HTH]

There's a load of info in this PDF regarding orientation and one of the tanks (4FB2B1A) at hot rox is centred for open side up... out of stock though. You could easily screen off the open side of a bottom mounting one and use long bolts to fasten it to the top of the head.

http://www.electricalfun.com/workben...everb_tank.pdf

Excellent, looks great - will have a proper read later on.

[jimboyogi]

If your willing to go transformer less for your tank drive, then you can definitely build a good sounding single tube reverb. I've built them with both a 12DW7 (as mentioned above), and also with a pentode/triode tube like a 6U8/ECF82.

For a tank you need one with high input impedance, if you skip the transformer. From my experience with these transformerless circuits, a 3 spring tank gives a much lusher reverb than a 2 spring.

[HTH]

I'm certainly not against any one way of doing things - to be fair, the Belton digital reverb module sounds great and would save lots of time and cost, I'm seriously considering it (freeing up a valve for some tremolo).

One thing that comes to mind with the vintage Fender reverb is that a paralleled 12AT7 would have an internal resistance of 5k5, so why is the reverb transformer 22k? On the stand alone reverb circuit using a 6V6, the reverb tx is 5k5 (which is what you'd expect to match up a SE 6V6 at).

[Gaz]

also, in practice, does it make any difference if you mount the reverb tray open side up or down? - this is to go in a head, so the open side would be up, however trying to find a reverb tray for sale designed for open side up installation is proving very tough - they're all open side down for combos.

Yes it does matter if you play loud enough. I recently mounted an open-side-down tank in a head, and found with the gain, volume, and reverb maxed I would get a low resonating feedback. Turning the head upside down (so that the tank was right side up) and placing on some rubber feet proved that it was the orientation of the tank because I could not coax it into feedback. I tried the same experiment with the head on its side as well, and again the feedback would happen.

Examining the tank more closely, I realized that with enough vibration the tray (mounted by the 4 corner springs) would hit the chassis, when mounted upside down like I had it. The tank was simply not design to hang that way. I thought about sealing the open side and mounting with long bolts as another poster suggested, but my OCD got the best of me, and I was determined to find another way.

My solution is pictured below, and all it took was moving the springs to another hole (why are all those holes there anyway?!). What this did was raise the tray a little so it would hit the pan - simple as that. I wonder why they don't do this in the first place?

My only cautionary advice is to be extremely careful removing and re-attaching the springs. They are very thin and flexible (to help with absorbtion), and can be stretched beyond repair. Don't ask me how I know this.

[HTH]

Thanks for the reply Gav (and everyone who's gave advice).

The problem I'm finding is that 99% of the tanks out there are for combos (i.e. open side down). The ones I've found for open-side-up orientation don't have the 8ohm input.

At this stage, I'm thinking that this is more trouble than its worth and the digital reverb module from Belton is looking more and more attractive.

[HTH]

essentially I need one of these tanks... 3AB3C1A

[Enzo]

Why are all those holes there? Because as you discovered on your own, that is the difference between the pan types. The holes allow the innards to be mounted a little each way and tighter or looser. Why didn't they do it in the first place? They would if it were a different pan number.

[Gaz]

Thanks, Enzo, that was my suspicion. I'm still a little puzzled as to why they don't just ship them like that since now the pan works both ways!

HTH, I'm not sure if there some confusion, but with the mod I posted you can use a open-side down pan with the open side up.

[HTH]

Thanks, Enzo, that was my suspicion. I'm still a little puzzled as to why they don't just ship them like that since now the pan works both ways!

HTH, I'm not sure if there some confusion, but with the mod I posted you can use a open-side down pan with the open side up.

Hi Gaz, the attachments you posted won't open for me so I can't see what you're suggesting.