6V6 Rocket

[sunnydaze]

Sorry about resurrecting this old topic, but folks on this string seem to have a pretty good understanding of something I'm a little confused about.

What is the purpose of R10 on the Rocket? This is the 220K resistor after the tone stack. I don't really think it's part of the tone stack. Is this functioning as grid stopper for one side of the PI?

The reason I ask, I'm considering a Rocket inspired build that uses a different type of tone stack.


Thanks
Mike

[Colossal]

Mike,

That lone 220k at the PI entrance is a remnant from the AC30 from which the Rocket's gets most of its DNA. Ken removed the lower 220k resistor from the AC30 and left the upper. Have a look at the 1994 Top Boost reissue schematic (lower right hand corner) and you'll see the 220k/220k divider in front of the PI.

http://www.blueguitar.org/new/schem/vox/ac30ripr.jpg

[sunnydaze]

Mike,

That lone 220k at the PI entrance is a remnant from the AC30 from which the Rocket's gets most of its DNA. Ken removed the lower 220k resistor from the AC30 and left the upper. Have a look at the 1994 Top Boost reissue schematic (lower right hand corner) and you'll see the 220k/220k divider in front of the PI.

http://www.blueguitar.org/new/schem/vox/ac30ripr.jpg

Thanks for the link Colossal. It look like the lower 220k was coming form the normal channel's volume pot. I can see why the Rocket wouldn't need that one.

OK, now I understand where the 220K came from - passed on from the AC 30. I'm still not sure I understand the purpose in the Rocket. It looks to be in series with one grid of the PI, although separated by the .047 cap - kind of looks like a grid stopper.

I'm considering building something similar to a Rocket from spare parts . I was thinking maybe a couple of couple of cathode biased 6L6's or similar tubes in the power section and a baxandal type tone stack. Not sure I need that resistor. I know it's easy enough to test with and without, and see which I like better. But I'd like to understand what purpose that resistor serves as used in the Rocket.

Comments, insights and observations would be greatly appreciated.

Thanks
Mike

Thanks
mike

[Gaz]

I've A/B that resistor a bajillion times, and found it make no appreciable difference to the tone. I suggest you do the same.

I believe that resistor is not functioning as a grid stopper because it is before the CC as you mentioned.

I do however prefer the 220k/220k divider, otherwise there is only a very small range of clean tone at loud volumes (that is with the guitar's volume all the way up, however).

[jjman]

That 220k is in line with the signal's path to ground so it's not a stopper. It's a dropper. Not dropping too much since there is still about 600k or so to get to ground after it.

[sunnydaze]

That 220k is in line with the signal's path to ground so it's not a stopper. It's a dropper. Not dropping too much since there is still about 600k or so to get to ground after it.

It seems like the path of least resistance would be though the grid of the PI rather than through that 1meg resistor that flushes through the PI tail to ground. Looking at it that way, I guess it's a voltage divider...But I'm a rookie and that .047 cap in the series confuses the issue.

Gaz>thanks for the comment. I'll let you know my experience if once I get the build to point to a/b ing that part.

Thanks
Mike

[jjman]

Thru-the-grid is the path of most resistance. Current does not flow thru the grid under "normal" conditions. When the grid gets closer to zero volts (compared to the cathode) current will flow, but this is "bad." This only happens during strong signals that can "saturate" the tube on the top of the input's voltage wave. So people place grid "stopper" resistors to curtail such current.

[sunnydaze]

Thru-the-grid is the path of most resistance. Current does not flow thru the grid under "normal" conditions. When the grid gets closer to zero volts (compared to the cathode) current will flow, but this is "bad." This only happens during strong signals that can "saturate" the tube on the top of the input's voltage wave. So people place grid "stopper" resistors to curtail such current.

Thanks, that explanation is helpful and correct. Based on what I just read on Randal Aiken's site the input impedance at the grid will be at least 2 - 5 times higher than grid resistor on the LTPI.

Continuuing my education process - Does the capacitor that's in series between the 220K resistor and the grid prevent the resistor from functioning as a grid stopper in non-normal situations in which the grid is conducting current?

Thanks
Mike