• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My New EL84 PP

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PRR

PRR

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Joined 2003
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baker8 said:
....a 100k grid to grid resistor that's parallel to the autoformer. ....explain the purpose of this resistor and how it's value is calculated?...
Click to expand...

You have a capacitor (not mentioned). You have an inductor (transformer).

L and C together will always resonate!

Your Standard Texts will cover this, but not in this exact form, and not as specific worked examples.

The resonance is damped by resistance(s). The tube rp for one, series to the LC. Generally we need/want another resistance. Koonw's plot shows that a simple LC can be optimally damped for a Butterworth (or other) corner at the band limit. The plot also shows how we do it these days: throw it in the simulator and ask The Idiot to sweep for an optimum.
 
S

Simply Audio

Member
Joined 2018
Hi, I was reading these posts with interest and note EP have an Autoformer to do phase splitting that could be used in conjunction with a capacitor for a PP EL84 amplifier.
Do Jensen or Cinemag also have a small phase splitting option, SE>PP
Maybe using a low Rp 1/2 ECC99 as a driver ?
There will still be extra residual current on the EL84's when they swing more positive under heavy bass notes etc.
Thanks
 
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