I am an inveterate tube roller and some circuits will not respond to tube changes.
I tried to cool off a highly modded ARC SP6B pre amp. It already had the reputatation of the "legendarby gain gone wild". You can't simply swap lower mu tubes to get a more viable midrange and travel on the volume pot. It takes 12AX7s x 6 and only Only 2 are in supposedly real meaningful gain positions.
Try as I might for example with top of the heap 5751s -2AU7s almost passed enough current to burn up my voice coils, the amp seemed to care less. The result was a change in tone very, little if any perceptable change in gain.
I tried to cool off a highly modded ARC SP6B pre amp. It already had the reputatation of the "legendarby gain gone wild". You can't simply swap lower mu tubes to get a more viable midrange and travel on the volume pot. It takes 12AX7s x 6 and only Only 2 are in supposedly real meaningful gain positions.
Try as I might for example with top of the heap 5751s -2AU7s almost passed enough current to burn up my voice coils, the amp seemed to care less. The result was a change in tone very, little if any perceptable change in gain.