Grid R's on board ok?

[azatplayer]

I read grid resistors are best attached to the tube socket with the shortest possible lead to prevent oscillation. Im in the midst of a build, and ive moved things around a bit as an experiment.
What im doing is a plexi in a tweed chassis, its real cramped, only 4 inches wide, and im using a PPIMV.
The MV pot sits directly opposite the centre of the power tubes. That also correlates to between the grid coupling caps. As im feeding the caps directly to the dualgangpats, just thought instead of running wires over the top or under board, using very short lead to the board, then 1.5K across the board, short lead down to the tube.
Im gonna try this anyways, if it ends up with a little oscillation (if i can hear it) then i can attach them directly. Just trying for a really really neat look.
Can still use that spot to run jumoers on the board i guess, then a grid R from board to socket. Its that tight i can run a Grid R from the turret direct and still have it right on the tube pin.

[paulster]

Im gonna try this anyways, if it ends up with a little oscillation (if i can hear it) then i can attach them directly. Just trying for a really really neat look.

The trouble is, you most often don't hear power tube parasitic oscillation, you just see it as premature red plating.

You really need to look at the output on a scope to determine if you have any oscillation since it's usually well outside the audible range.

I'd put the resistors on the tube sockets.

[azatplayer]

Yeah i think i allready came to that conclusion. Will just place a jumper on the board or run the grid wires under. Will work it out.

Another question, reading Aikins grounding deal, he suggests that the grounds from the EL34 sockets should be run back to the first PS caps ground.
Rather than at the socket. Cant say ive seen that done. Anyone do this as a rule?

[iknowjohnny]

Just none example and it may not represent typical operation, but I have 3 amps with the grid resistors on the board and i never noticed any issues. I then moved them on th4e latest amp to the tube socket and nothing changed that i could tell. But we know it's not supposed to be good so on my new build they're on the socket.

[tubeswell]

Yeah i think i allready came to that conclusion. Will just place a jumper on the board or run the grid wires under. Will work it out.

Another question, reading Aikins grounding deal, he suggests that the grounds from the EL34 sockets should be run back to the first PS caps ground.
Rather than at the socket. Cant say ive seen that done. Anyone do this as a rule?

Yep I do that with all my amps, and I run the output tube grid load resistor to that same filter cap ground as well, and the HT winding centre tap (and all the 'hi-current' ground returns). I ground all the lo-current pre-amp returns - together the pre-amp filter cap ground- at the input jack ground. I don't have any issue with hum.

Merlin Blencowe recommends going one step further in his interesting article on his website about grounding. He recommends tying the ground returns of the stage to the relevant decoupling cap (assuming there are several caps throughout the amp). The article 1st appeared at the end of his new book, but the one on his website is in an updated form.

http://www.freewebs.com/valvewizard2/grounding.html

[paulster]

Merlin's grounding scheme is pretty much what I use, to keep current loops short and locally contained.

It makes for a very quiet and stable amp, even with massive gain.

[crbowman]

Back to the grid resistors, first amp I built was a little Spitfire clone. Sounded great until it was dimed and then it had this annoying fizziness. After several months of tweaking, I moved the grid resistors off the board and put them directly on the tube sockets. Low to moderate volumes sounded the same but dimed it was louder, much tighter and punchier, and the fizziness was gone.
Made a believer out of me.