Bugera 333XL doides control grid to ground?

[Enzo]

It isn't a plate, it is a ground. There are multiple grounds, this one is the F group. Note that without that F connection there would be no ground connection for the power tube cathodes. It goes off the sheet over to the left and becomes GND there.

[Mike Sulzer]

It isn't a plate, it is a ground. There are multiple grounds, this one is the F group. Note that without that F connection there would be no ground connection for the power tube cathodes. It goes off the sheet over to the left and becomes GND there.

So the horizontal line is meant to represent a piece of a longer heavy wire, or ground bus. That is not a great way to do it.

[bob p]

Like it or not, that seems to be the standard way that star grounds get drawn on schematics produced by CAD systems.

[bob p]

Looking at that schematic, I'm at a loss to explain why they didn't replace that 4007 with a zener and put an opposing 4007 from ground to it's cathode.

[Enzo]

That line is the consistent symbol for ground all over the schematic. the A. B, C, D, E, F represent the subsections. The schematic shows where the subsections join as well.

bob, where?
The power tube diodes? The cathode is already ground, so you want to lift the cathodes and insert diodes? The existing grid diodes do not conduct until the grid peaks go positive. Making it a zener does what then? Allows the grid to go the zener voltage positive before shunting? Or shunts zener volts before grid conduction? Unclear what you are suggesting. To me, at least.

[Dave H]

Looking at that schematic, I'm at a loss to explain why they didn't replace that 4007 with a zener and put an opposing 4007 from ground to it's cathode.

That sounds like a mod you'd do to a cathode biased amp.

[bob p]

Dave got the joke.

[Alex R]

The grids are sitting there biased to -45v or whatever. So those diodes only conduct if the signal peaks are larger than 45v on the positive side. Most of the time that won't happen. But if you did manage to shove an over 90v p-p signal into those grids, the diodes would turn on for the positive peaks over 45v. SO your signal would have positive peaks clipped off. The purpose of the diodes is to prevent the grids going positive and drawing current.

Keep your signal below 90v p-p and the diodes will never do anything. They ONLY conduct for the portion of the signal OVER 45v.


And in every place I wrote 45v, you can change to whatever the actual bias voltage is in your amp.

Ah of course, the bias voltage, dur. Thanks Enzo!