47 Ohms Above Ground

[silverfox]

FWIW, I found an error in the schematic. It has nothing to do with this topic, but, makes me wonder if the whole 47 ohm issue is going to turn out to have a print error in it.

The error I found is related to the Screen and Plate voltage connector. It lists the screen voltage as a ground on the power board. At least that is what the print looks like in the Power Board Layout. Fortunately I didn't understand the grounding scheme here so I've been tracing out all the grounds and found that before powering 475 volts to ground.

I do bring everything up on a Variac first though for reasons like that.

Here is another thought. I've noticed all the grounds are grouped symbolically, I'm learning that... In the schematic it appears the shorting grounds on the 47 ohm resistor are separated by capacitors so the middle stages of the preamp are lifted. Is this correct? I don't think they are showing a physical separation between grounds. However, taken literally when you simply go by the ground symbol groupings it would read that way. (This is a theory- I could be wrong)

Thanks again for all the efforts.

[Enzo]

The 47 ohms are not misprints or errors, they are there. Yours is between V4 and V5.So if I read you right, the error is on the layout, not the schematic?

I don't spot an error, can you be more specific? On the power board layout I see a three pin connector upper right. Left to right screen-ground-plate. Ground is shown as the vcenter pin, wired to the filter cap negatives and the anodes of the rectifiers. The left pin is the screen node, and is shown wired to the standby switch and C51. The right pin for plates is shown wired to the rectifier cathodes and C49. That is consistent with the schematic as far as I can tell. Am I overlooking something?

Oh, I think I see what you are looking at. I got out my paper copy to check. The screen one looks like it might say "SCREEN GND" next to it, but it is unclear even on the paper. I think it equally likely it says "SCREEN GRD" GRID, not GROUND.


The grounds are grouped symbolically, they are also grouped on the boards. Those various grounds are then joined in some fashion or another. There are ground joinings all over this print. I see two, including the phantom 47 ohmer, in the center left of the title. ANother below the speaker jacks, and also left of the reverb control. And up below V1. Also the input jack joins two grounds. And the gootswitch jack too. I don;t see the capacitors you report, where are you looking?

Using my description as rake and triangle symbols, the V1 V2 stage triangle grounds go to chassis at the input jack. The circled triangle grounds of the tone stacks and the pump stage to have a 47 ohm to the boxed rake but they also are joined by the ground joint just below the pump control to the input jack ground. A similar connection is made below the reverb return. If you look around, all the rakes are joined and connected to chassis, that is plain rake, circles rake and boxed rake. So neither end of that 47 ohm is lifted, nor are any of the grounds.

[silverfox]

Grid-Ground

Yes, perhaps that was it. Grid. As for the grounds, this is all beneficial as limited build experience creates these long pauses before I actually make a connection at times. But I'm getting there.

I think this is a local ground scheme that in places is then joined to some other ground point. Most facinating.

Thanks,

Silverfox.