Grid Values

[C Moore]

On an Express.....
Any of you guys use something other than a 1.5k grid resistor?
Thank You

[TheGimp]

The Grid resistors in the output circuit are Grid-Stop resistors which are there to prevent high frequency oscillations.

The values are non critical, other than making them too large (>10K) will effect the high frequency response of the amp (in conjunction with the grid capacitanc). Since pentodes are used in the output, Miller Capacitance is low and not a major issue.

Best to stick to values in the 5K-1K range. Too small may not suppress oscillations.

This is one of the few locations where CC resistors are arguably well suited since they have no spyral film pattern to make them inductive (sub-nH range so I still consider it not be an issue).

[dartanion]

Changes within 1.5k to 5k are audible. This has been argued over and over, however it is definitely audible. It's one method of tuning the power amp.

[PCollen]

On an Express.....
Any of you guys use something other than a 1.5k grid resistor?
Thank You

Since you're probably driving EL34's , try the 5.6K value a la Marshall and see if you hear a difference.

[C Moore]

On an Express.....
Any of you guys use something other than a 1.5k grid resistor?
Thank You

Since you're probably driving EL34's , try the 5.6K value a la Marshall and see if you hear a difference.

Yeah, 34's.
It has been several months since I have been inside this amp. I was kind of surprised to see I had switched to 4.7k on the grids. To be honest, I cannot remember why I made the change. The amp sounds pretty good (finally) so I am wondering what some of you other guys have at the grids of your EL34 Express....and why
Thanks

[M Fowler]

What about the Rocket using 1k verses 100R?

[paulster]

What about the Rocket using 1k verses 100R?

That's the screen grid rather than the control grid that the OP is talking about in this case.

[M Fowler]

I shouldn't be thinking about amps when I'm sick and brain dead, thanks.