Fender Grounding Scheme

[martin manning]

Geez... how many time has this one been debated...

Anyway, I have a specific question: I've been studying the Fender 6G16 Vibroverb layout, which doesn't give the details of the wiring of the filter caps under the doghouse. I *think* that only the first filter ground (two 16 uF's in parallel) is run over to the PT area and soldered to the chassis, while all of the other caps (the ones from the nodes labeled B, C, and D on the B+) have their grounds tied together on the filter board and then that junction is taken inside and soldered to the chassis near the input stages.

Is this right? There are few pictures available with the cap cover off. If so, would it not be better to take the ground of the second filter (B node, immediately after the choke on the B+, which is feeding the screens) along with the first filter over to the PT?

Do other (later) Fenders with the grounds taken inside the chassis have the same arrangement in this regard? (I know that the earlier amps, like the 5F6-A had all the filters grounded to the doghouse itself)

MPM

[StratTone]

Yeah I think most people tend to connect the grounds under the doghouse now and run to the PT ground.

[MWJB]

Typically a 6G16 would be running 470vdc+ nowadays, so scrap the 2x16uf 450v in parallel idea and put the main filters in series, 2x100uf caps at 350v (50uf total), each cap bypassed with a 220K 2W resistor.

Usually the main filter caps are jumpered together under the board and grounded near to the PT. Screen, PI & preamp caps are jumpered under the board and grounded to the brass plate next to the normal channel input jacks.

I would ground main & screen caps to a PT bolt/chassis by the PT, but run a ground wire for each node. Likewise, PI & preamp caps, seperate wire for each cap, both grounded to Normal input jack #1.

[martin manning]

Thanks for kicking this back to life StratTone.

MWJB, I'm a little better informed regarding grounding issues now, and I agree with your suggestions.

I think the original Fender layout did ground the screen filter with the preamp stages, which doesn't seem like a good idea. The jumpers are under the cap board, and so I can only go by a picture of a recap job in progress that I found. Also, a recent exchange with someone doing a recap on a Super revealed the same thing (and that one now has a caps-in-series-with-balancing-resistors arrangement for the first filter).

Fender's layout definitely shows only one wire for each of two grounds- one going to the chassis near the PT and one to the brass plate. Maybe it's better to ground the screens with the preamps if there is only going to be two ground wires total?

MPM

[StratTone]

Thanks for kicking this back to life StratTone.

MWJB, I'm a little better informed regarding grounding issues now, and I agree with your suggestions.

I think the original Fender layout did ground the screen filter with the preamp stages, which doesn't seem like a good idea. The jumpers are under the cap board, and so I can only go by a picture of a recap job in progress that I found. Also, a recent exchange with someone doing a recap on a Super revealed the same thing (and that one now has a caps-in-series-with-balancing-resistors arrangement for the first filter).

Fender's layout definitely shows only one wire for each of two grounds- one going to the chassis near the PT and one to the brass plate. Maybe it's better to ground the screens with the preamps if there is only going to be two ground wires total?

MPM

I'm not to totally sure what everyone does. I'm sure we all have our way. lol I really just like to ground the totum pole with the PT center taps and cathode grounds of the power tubes. The other three under the dog house I ususally tie to the buss ground I make with pots and jacks. To me it is a nice balance between clean and not to much noise. I've never been one to care for a dead quite amp with a messy looking star ground or 3. lol I've tried most grounding schemes and been happy with all.

[MWJB]

Don't use 2 ground wires total is the message. Run 2 ground wires out to the PT from mains & screens, run 2 (PI & preamp) ground wires to the input jack/brass plate.

Fenders were well made at this time, but they were still mass produced amps...you have the benefit of being able to take a little more time with the build & eliminate possible gremlins along the way.