Need Ground connection on Reverb Transformer Black wire?

[ac427v]

I built a Deluxe Reverb variant that originally had reverb hum problems. Multiple mods including isolation washers on all 4 RCA jacks solved that.

The reverb return, reverb foot-switch, and trem foot-switch are all connected to a buss that grounds at the cathode ground of the reverb recovery triode V3a.

The black wire from the reverb transformer is connected to the ungrounded shield of the "send to tank" jack. It is not grounded to the chassis. Everything seems to work fine at apartment volume. I have jumpered the black wire to a chassis bolt and also to the RCA buss with no change audible at low volume.


Should I ground the Black wire because of reasons I am not aware of?

[Latole]

Is the chassis is the ground for the amp?
If so, the shielded cable must necessarily be at ground, contrary to what you would have observed, and the black wire of the reverb transformer is connected to ground.

You also write that the amp works well.
So everything must be correct, no need to look for problems

Original Fender DR  reverb circuit

[Willabe]

On those reverb tanks and their 2 cables/send/return, only 1 RCA jack on the tank should be grounded to the verb tanks housing. This is so you don't get a ground loop.

From amp chassis to the verb send RCA jack ground, through the send/input verb cables shield, to the verb tanks input RCA ground on the verb tank housing, through the tanks housing, back out through the verb tanks return RCA, to the return cables shield, back into the chassis' verb return RCA jack that's grounded to the chassis and round and round it goes.

Have to break that loop somewhere.  Usually it's broken at either 1 of the verb tanks RCA jacks, isolated jack, or 1 of the cables the shield is only connected/soldered at 1 end, not at both RCA jacks ground lug.

And the tubes for the verb, the driver and the recovery, are fed from different B+ nodes. So they don't get grounded together. The driver gets grounded with the B+ filter cap node that feeds it and the recovery circuit gets grounded with the B+ filter cap node that feeds it.

Read this from Merlin on grounding if you haven't yet; 

https://www.valvewizard.co.uk/Grounding.html

[ac427v]

Much thanks all.
My reverb tank input jack is insulated from the tank. So no ground loop. The shield of the cable does connect to the reverb transducer coil. The other end of the transducer coil is connected to the center conductor on white reverb cable.


Merlin does not address connections to isolated reverb RCA jacks in his grounding chapter (thanks for the reference though).

Latole's concern that the shield of the white send cable needs to be connected to ground at the amp end to allow it to function as a shield makes sense to me. It sounds like I should connect the white RCA ground lug and the black reverb secondary lead to the preamp ground buss at the negative end of the reverb driver cathode capacitor. In the morning...

[Willabe]

Merlin does not address connections to isolated reverb RCA jacks in his grounding chapter (thanks for the reference though).

Not the point. It doesn't matter what the circuit is, preamp, PI, reverb, tremolo, etc. What matters is making a ground star from all the grounds of the circuit and grounding them with the B+ filter cap that feeds that circuit.

And the tubes for the verb, the driver and the recovery, are fed from different B+ nodes. So they don't get grounded together. The driver gets grounded with the B+ filter cap node that feeds it and the recovery circuit gets grounded with the B+ filter cap node that feeds it.

Read this from Merlin on grounding if you haven't yet; 

https://www.valvewizard.co.uk/Grounding.html

It sounds like I should connect the white RCA ground lug and the black reverb secondary lead to the preamp ground buss at the negative end of the reverb driver cathode capacitor.

No, see above. All the verb driver tube grounds go together, the driver tubes grid return R, it's K (cathode) R and K bypass cap, the verb transformers secondary ground wire and the send RCA ground. That ground stars leads go to the ground lead of the B+ filter cap that feeds that verb tube. Which is probably the power tubes screen grid filter cap, B+ node B. And this star gets grounded with the power amp ground.

The verb recovery tubes grounds get gathered together and they go to the B+ filter caps ground lead that feeds the recovery tube. Then that ground star has a wire that goes from that ground star to the preamp buss.

[SEL49]

My reverb tank input jack is insulated from the tank.

Fender never insulated the reverb phono jacks from chassis. Look at how Hoffman does his reverb grounding...

     https://el34world.com/charts/grounds.htm

[Latole]

If the amp works perfectly well, as ac427v writes, it means that the assembly is well done.

As the saying goes: “If it ain't broke, don't fix it.

[Merlin]

Are you are saying the connections between the reverb trasformer, and the tank input, are completely floating with no connection to ground whatever? If so, you probably do want to ground the black wire to chassis to ensure hum rejection, since it is the shield of the cable. Typically you would make this connection at the 'send' phono jack.

[ac427v]

Are you are saying the connections between the reverb trasformer, and the tank input, are completely floating with no connection to ground whatever? If so, you probably do want to ground the black wire to chassis to ensure hum rejection, since it is the shield of the cable. Typically you would make this connection at the 'send' phono jack.

Yes, completely floating. The isolated phono jacks were part of my effort to get the reverb hum-free. Typically I stay with Fender and Hoffman layouts but in this case I put a Deluxe Reverb variant in a Princeton Reverb chassis and needed a unique layout to fit everything. Unique means many wheels to reinvent


I will connect the black wire to ground.


Thank you so much Merlin, for advising me and for being part of this forum. Your knowledge and experience are amazing!
I appreciate the knowledge and advice of others too. I benefit from their experience through this thread and the many other threads that help even if I have not started them.