Getting Reverb hum, please help!

[Nathan]

Hi guys, it's been a while since I dropped in here. Hope all are well?


I built a faux Sawrt AST a number of years ago. It has a transformer-less reverb using a 12DW7.


Now the first Accutronics tank I bought was the same Swart uses, a 8FB3C1C. It arrived dead and caused me a lot of grief because I couldn't wrap my head around a brand new tank being defective. Anyway, I bought another, this time a 8FB3C1B (I think -it's the same but jacks mounted upward). The verb worked and sounded fine until I heard another real AST and the sound was way more pronounced and lush.


So I thought to myself what would a long-spring version sound like? I have the luxury of making my own cabinet, so I'm not restricted by width. I bought a MOD 4FB3D1B. It sounds full and amazing like I heard before! Only one problem: there's hum. It goes away when I touch the casing, so I know it's has to be a grounding issue, but I am not wise enough to know what to do!
The D means "Input Insulated / Output Insulated" so that must mean the casing is not grounded at all?


Can you guys school me? I realize it should be a simple fix, but I just can't figure out how the grounding works at the jacks.


Thank you so much! 

[sluckey]

Try this. Turn the tank upside down so you can see the springs. Connect a gator clip lead to the metal housing. Connect the other end of the clip lead to the output RCA jack shell terminal (not center pin terminal). Does that help? If so make that ground connection permanent. May need to drill a screw hole for a chassis ground lug.

If no better, repeat above for the input RCA jack.

[PRR]

There are too many variant tank models.

Some have the shell strapped to an RCA jack, some don't. (Usually to the weak output side, but I think they can also be had grounded to the driver side RCA.)

Less hum when touched (AND you are somehow groundy) suggests that the tank case is not grounded.

Sluckey's clip-lead test is THE way to confirm (or deny). If the cliplead is a cure, do the same only so it won't fall off (wire plus screws, nuts, whatever).

[Nathan]

Yup, sluckey nailed it. Thanks!!


On a side note, the weaker reverb I heard from the Accutronics tank was because I was using the WRONG one from a Blues Jr with a different input impedance (8DB...). Where's the dunce cap smiley?