I have an old hammond amp that I am converting for guitar, the amp worked before but now I only get sound for maybe a second after it warms up then the sound fades out to nothing. If I turn it off for a second then turn it back on I get another second or so of sound then nothing, any ideas?
Every valve grid must get a DC supply from somewhere.
Not always it is true. In a work called "Some augmented cathode follower" the author explain that if you leave the grid without DC return, the positive and negative grid currents cancels out, and then the tube gets his own bias.
I said secondary emission. The higher the positive charge on the grid the greater will be secondary emission as electrons will strike with greater momentum so more likely to cause secondary emission. A grid can be coated to suppress secondary emission, of course, but keeping its voltage low will always help.
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