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What has worked mostly for me to massively reduce/ eliminate the issue is.

After stumbling across a vox ac30 reissue noise post ( resolution was to move the grid resistors off the board and directly to the tubes) And looking at the way they run the connections on the big Marshall builds

I initially put jumpers in place of the 8k2's and new resistors connected directly at pin 2 with existing wire. But since I only had some 2watt MO power resistors (didn't want to mess up the ccs yet) stuck them in and low and behold the fizzys where almost gone but the MO's where brittle sounding.

So I stuck the ccs in directly mounted to the tubes and the fizzys where back. At this point I remove the jumpers I put in place of the grid resistors on the board and did a twisted pair of wires directly from the two 470k. Ran the wires under the board and connected directly to the tubes and at this point with the cc's and the fizzys where reduced .

Today i stuck in a couple of 2w cf resistors (what i could find at sayal) an voila the fizzys seem to be gone !

Interesting . Put one end on pin 8 and the other on pin 2 like we did in the new v6. We did think about doing them all this way actually. Like we build the JTM45. But fizzies have not been such an issue. Worth some testing at our end too.

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Stephen
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With putting the resistor as close as you can to the actual grid you are effectively improving the performance of the low pass filter the tube forms.

The grid stopper combines with the Miller capacitance of the tube to work a low pass filter. The filter is used to block unwanted high frequencies but I suppose putting the resistor closer to the tube could somehow limit grid current.

If you want to keep the output tube’s grid wires short and mount the resistor close check out Trinity’s Plexi Brown (white wires)
download/file.php?id=755&mode=view

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