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Gridleak resistor value for 6F6G
#1
Hello, im building a true class A amp with a choke input filter and cathode bias with four 6F6G tubes in the output. 
I noticed in several of the cathode biased fender tweed amps that the grid leak resistors to both the 6v6 and 6l6 setups is 250k. Since both of those are tetrodes which are more efficient than a true pentode like a 6F6G, i wonder if a higher gridleak resistor value would be a good idea. Currently on my board i have soldered in two 560k gridleaks to ground (one for each output pair ) However, i think 560k may be too high, and was wondering if 330k would be a better value for these tubes?  Also, how do you determine what value to use in the first place for any given output tube? The topology is 6sj7->6sl7->6sn7->two or four 6F6G (#42) tubes.   Thank you for your thoughtful replys

Other considerations, so its 6sj7 gainstage-> 1/2 6sl7 gainstage -> 2/2 6sl7 gainstage-> bandmaster tonestack->6sn7 phase inverter-> then 6f6g output pair.

I read that the bandmaster TS is pretty high impedance and somwhat lossy , also i am NOT using a cathodyne PI as the tweeds do, im trying to get higher voltage swing from the PI to really distort the output tubes, and since the amp is class A there is much lower B+ than would be required to use the cathodyne to achieve this.
Probably 315 VDC at the first node WITHOUT any tubes installed to draw current.
The Amp is currently under construction so no tests or checks are possible yet, but will be soon. Im just trying to tie up loose ends before i solder any further.
A bonus question in addition to the grid leak value for 6F6G,, is one for the preamp, I basically ran the 6sj7 champ circuit right into 1/2 of the 6sl7 for the next fain stage. What would be the appropriate grid stopper and gridleak value 6sj7 going into 6sl7?
Thank heeps
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#2
I am not intimate with 6F6g characteristics so cannot recommend a specific value of grid leak for you.  Like most things in engineering, determining a good value for the grid leak resistor is a trade off.  It is effectively the load for the previous stage at low frequency.  So if you want more gain from the previous stage, you want a larger grid leak resistor to a point.  However, the output tubes Miller capacitance forms low pass filter with the previous stages output impedance which the power stage grid leak resistor plays a significant role in.  This can be helpful for smoothing phase inverter distortion but at some point high end is lost.  It is worth noting that there is a max grid resistance value listed on many datasheets.  This value is commonly exceeded in many guitar amp designs for the reasons above and is “allowed” because of local negative feedback or reduced dissipation limiting thermal run away.  So long and short, it depends on your goals for gain and frequency limiting at that point in the amp design.

Aiken amps has a series of white papers that you may find helpful in your efforts.  Particularly this one:

https://www.aikenamps.com/index.php/desi...amplifiers

Look for the section on Rg.  Though it is discussing a triode gain stage the concepts are the same.
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#3
According to the data sheet, the grid resistance is not to exceed 500k for the 6F6G.
So im within limits on that aspect if i use anything below that.
Im sure id want the value to be such that it reduces bass. Does that mean more or less grid resistance?
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