reverb tanks that are grounded on both ends, which end to chassis ground?

[Chipper]

When using reverb tanks that are grounded on both ends like 8AB1A1B (Connector Type: Grounded Input, Grounded Output), which end of the tank should be connected to chassis ground?  I don't think you would want to connect both to ground because of potential ground loop.  I am mainly concerned which is better for low noise but if safety is in the mix might be interesting to talk about.  Thank you.

[DummyLoad]

the return path is most susceptible to power grid & RF pollution. return jack should be the path to ground via shielded cable.


--pete

[HotBluePlates]

When using reverb tanks that are grounded on both ends like 8AB1A1B (Connector Type: Grounded Input, Grounded Output), which end of the tank should be connected to chassis ground?  I don't think you would want to connect both to ground because of potential ground loop.  ...

When you connect one jack to the amplifier's chassis ground, you've connected both to ground & completed the loop.  This is why Fender always used an "Input Isolated, Output Grounded" type of tank.  The reason the above is true is the ground portion of the RCA jacks are riveted to the tank's metal case to "ground" them.

You can use one of those tanks, but you'll need to remove the original RCA Input jack and install a new one isolated from the tank's shell.

[Latole]

Update 10:26

I have a brand new Accutronics 4AB3C1B( for Fender)  and 4EB3C1B ( for Traynor) at home.

Output RCA jack ( red ) il grounded to the tank case / body
Input  RCA jack (white) is insulated from the case/ body

I hope it help.

[sluckey]

Here's what Accutronics says about their tanks...

Connector Grounding/Insulating

In order to suit any grounding scheme, reverb tank connectors come in all combinations of input
and output insulated and non-insulated phono jacks (a.k.a. RCA jack). A non-insulated phono jack
is one whose outer shell is grounded to the outer steel channel (chassis) of the reverb tank. Vintage
Accutronics® specs recommend insulating both input and output connectors and grounding the tank
chassis separately.

If the amplifier’s connection to the reverb tank’s phono jack shell is not at ground potential, it is
important that the tank be chosen with an insulated connector at that connection point. If the amp’s
connection to the reverb tank’s phono jack shell is at ground potential, either insulated or grounded
connector may be used at that connection point.

I have a brand new Accutronics 4AB3CB1( for Fender)  and 4EB3C1B ( for Traynor) at home.

4AB3CB1 is not a valid number. Fender tube amps use the 4AB3C1B tank.

[Latole]

I have a brand new Accutronics 4AB3CB1( for Fender)  and 4EB3C1B ( for Traynor) at home.

4AB3CB1 is not a valid number. Fender tube amps use the 4AB3C1B tank.
[/quote]

Thank's.
Typo error 

[ac427v]

Timely topic! I'm working on reverb hum in my mini PR. It has a Mod 8AB2A1B tank that is grounded at both ends. Each jack has a small printed circuit board riveted to the tank chassis and riveted to the jack. After reading about isolating the jack I used my Dremel to cut the trace on the board in two places. I now measure infinite resistance between the two jack grounding points. Previously they measured 0 ohms. I will update with the hum reaction later to day after reassembling. The cuts show as white on the photo.

[DummyLoad]

It has a Mod 8AB2A1B tank that is grounded at both ends.

couldn't you have simply used an isolated chassis jack? the secondary of the reverb driver transformer would then connect to tank for ground path via the tank output connector.

--pete

[ac427v]

 You mean isolate the send jack on the amp chassis? Didn't think of that! I was laser focused on isolating the white jack on the reverb unit in the easiest possible way. Next time...

[DummyLoad]

You mean isolate the send jack on the amp chassis?
yes. 

--pete

[ac427v]

Thanks Chipper for asking the question. Isolating my tank input cut hum by more than half. Good luck with your build.-Craig

[Williamblake]

I dont have many amps built but consider it known best practice to keep shielding apart from the circuit and break ground connections in the tank. Connecting tank shield to chassis and giving reverb in and out it's own connections to 0V. Reverb chassis to ground is a soldered bridge anyway making this easy.

[wsscott]

I saw this topic and thought it was interesting, but wanted to clarify a point.  Maybe it will clear up the hum I have when the reverb is turned on.

I'm using a MOD 4FB3A1B tank which is designed as Grounded at both its Input and Output.

When I built the amp I installed insulated RCA connector jacks into the amp's chassis, and connected the Ground tabs on both of these jacks to the Ground BUSS wire. So really the insulated jacks are not serving their intended purpose. The tank is not separately grounded to anything.

So are you saying that I should remove the Grounding wire at the reverb tank's input jack in the Driver and only leave it grounded at the output jack in the Recovery?

[sluckey]

So are you saying that I should remove the Grounding wire at the reverb tank's input jack in the Driver and only leave it grounded at the output jack in the Recovery?

Try it and see.

It would be important to know which circuit you are talking about.

Does the hum go away if you unplug the footswitch?

[wsscott]

I haven't disconnected the input wire yet, so its the same.

This is the Reverb circuit from the Magnatone 10A that you helped me build a "ReVibe Mod" headunit with Vibrato several years ago.  So it's the tube reverb from that amp.

When the Reverb Footswitch is Plugged in to the Reverb Jack, and the Reverb is switched OFF at the foot switch, there is almost NO Hum.

When I then unplug the foot switch from the jack, the HUM appears.

If the foot switch is plugged in, and Reverb turned ON, there is HUM.
If the foot switch is removed, and Reverb is still turned ON, there is HUM.  The HUM remains.

[astronomicum]

I used my Dremel to cut the trace on the board in two places

For future reference, there are two solder tabs, one on each side of the ground wire, that join the ground wire to the traces; a solder "jumper" in other words. A little solder wick and they can be removed, isolating the ground. Revisit tanks use the same arrangement.

[wsscott]

Thanks.  I saw that about the tabs.  My reverb is a tube reverb, and doesn't use a transformer.  As a result, the impedance of the reverb tank is a lot higher, like 1475 ohms input and 2250 ohms output.  I think most of the tanks run with a transformer are around 8 ohms.  So I didn't know if the really high impedance is what's causing the hum when the reverb is turned on, and so its just inherent in the design, or if its something else, like maybe a ground loop created by the wiring on the RCA jacks.  I didn't want to start futzing with the wiring until I had a better idea on the cause.

[wsscott]

Here's the wiring layout diagram if anyone is interested.

[shooter]

flying all those grounds over the board, is a recipe for hum.

[wsscott]

Shooter-Perhaps so.  But why do I only have hum when the Reverb is ON?  When it's Off, the head is as quiet as my other amps.  It seems to me its all in the Reverb Driver/Recovery.

[shooter]

should be easy to gator-clip the REV-IN ground tab to chassis, see if things "change"  looks like that tab is your "ground-point" for the Rev tubes?

[wsscott]

The Reverb IN ground tab connects to the Ground BUSS.   So would what you suggest be any different?

[shooter]

after flying through the air for 6".  By grounding "away" from that buss, the chassis can help "scatter" sneaky AC

[wsscott]

Where do you suggest I ground it?

[wsscott]

Shooter--V4 is the Vibrato/Oscillator Driver and V6 and V7 are the Reverb Driver and Recovery tubes.

I"ll try clipping in a lead from that Reverb In ground lug point just to the chassis directly and let you know what happens.

[wsscott]

Jumper connected from R-In jack GND lug to Chassis, no difference, HUM is still there.

Removed lead from R-In jack GND lug, no difference, HUM is still there, whether jumpered or not.

Note:  With lead disconnected from GND lug as above, GND lug has continuity with chassis GND if the RCA plug is inserted in the jack. If RCA plug is removed from R-IN jack , NO continuity with GND.

SO, the Input jack of the Reverb Tank is providing GND.  This Tank comes with BOTH the Input and Output Jacks Grounded.

Should I remove the trace to the Input Jack as suggested in this thread?  Or is there something else to try?

[wsscott]

Sluckey-Do you have a wiring Layout of the Reverb circuit that you did with the Mag 10A, or another amp that uses the same tube Reverb circuit, that you would be willing to share?  Maybe the way you wired it eliminates the hum.  I've been working with Astronomicum to see if we can find it, and it seems that it may be associated with the grounding of the reverb tank.  Anyway, thanks for your time.

[sluckey]

No layout. All I did was put together a schematic.

[wsscott]

Thanks anyway.

[wsscott]

SOLVED the problem.  It basically was a ground loop, I think. When I wired the circuit I questioned how to wire the connection from the backside lug of the 1M Revibe Pot to the Reverb Foot Switch to ground.  I had wired the lug to the Ground BUSS, and also wired the Foot Switch jack Ground lug to that same point.  I finally realized that created a ground loop.  So I removed the connection from the pot to the BUSS, and then connected the Ground Lug on the Footswitch to a new connection to chassis ground.  So when I hit the switch it makes the connection to ground at only one point.  Seems to have solved the problem.

Thanks for everyone's time and help.