EF86 triode connection variant

[noac]

Hello!!,

I have a question regarding to the triode connection of an EF86. I know the usual way to connect the screen grid to plate. But reading the Merlin's book on amplifiers (the hifi version, section 4.8.1, page 189), I came across a new flavour. Merlin proposes to just ground the plate to make a triode strapped connection. Merlin calls this way the "low-capacitance mode", and states that it might have some benefits, such as reducing heater hum.

- Would it be possible to make this mod in a guitar amp?
- Can you switch it on the fly?

I attach a picture the schematic.

Eager to see your replies!

[tubeswell]

Thinking about guitar amps, if you rely on the screen as the output electrode, you can't run the tube as hard (because of the lower g2Pmax), so it kinda defeats the purpose in a guitar amp (where you want guitary-amp things, like distortion and harmonic distortion etc, to happen). 


Besides, in a guitar amp, the amount of reduced heater hum you would get (in comparison to other possible sources of hum), probably means that this isn't worth pursuing. And any potential additional benefits from the grounded plate becoming another electrostatic shield are minuscule if you use a screening can (because that's grounded anyway).


For a triode option with EF86, I vote for one of his 'designing tube guitar preamp' mods (like the triode-pentode morph control). Others may have different views. YMMV

[PRR]

With 100K or more "plate" resistor, you won't overheat the screen.

The BBC used this ploy in a portable microphone amplifier to avoid the weight of shields.

I don't see any advantage in a guitar amplifier where levels are higher and weight is typicically not SO critical. With respect to Merlin, I don't see how heater hum is a factor. If you try it, please report.