Historically, tubes might have been expected to survive the abuse. I'd say it's capability of old-production tubes, copying of historical amp circuits, and a modern perspective of "protection circuits" that results in Valve Wizard suggesting a best-practice that wasn't seen in old amps. The question is: why? Is the issue that Valve Wizard describes overblown?Īin't no thing to add it to the circuit, but since I see it nowhere but on his page, and it doesn't seem to be discussed at all beyond this paragraph on that page, I'm curious why.Ī combination of reasons causes you to not see it elsewhere. In my build-up to a Bassman modification and looking at various CF/tone stack circuits, mainly in Marshall and Marshall-inspired schematics, I see nothing like this pair added. It is not unknown for this to cause arcing between the electrodes, and rapid destruction of the valve, even when a standby switch is used."Īnd then proposes adding a resistor and diode to prevent this. The traditional arrangement suffers from the problem that on startup, the grid will immediately rise to HT potential while the cathode is still cold, at ground potential. "It is very common to see a DC-coupled cathode follower in a guitar amp, often before a tone stack. The topic is inspired directly from this page:
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