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Discussion in 'Shock Brother's DIY Amps' started by Stan Martin, Aug 26, 2010.
to an 18 watt Marshall clone. schems/diagram would be great
Here's a schematic:
Click on Next for a pic of it installed.
Dual-gang 500k audio-taper pot, two 2.2M resistors and some wire is all you need.
The problem with using those values is the max grid leak resistance is around 407k. 18 Watters use 470k for their characteristic EL84 output drive. There's also a sweet spot around 415-430k that you'd be missing using these values. A better choice (and more common) is the 1M pot in parallel with 1M resistor shown below. At max it should read ≈500k.
A major advantage of the snorkle monkey circuit, it's fail safe. Even if that pot completely falls apart you don't lose bias.
This is important in any bias circuit design or mod, it should fail into a safe mode.