• 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.

What size capacitor I use for a 2A3 or 300B cathode bypass?

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sgerus

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Joined 2005
Sounds like you guys suspect the pentode is the cause of my poor high frequency response.

Initially I set up the pentode for the highest current and a lower Av.
(My logic was get the highest current possible to overcome the miller capacitance)
60K @ plate
510R @ cathode = 4mA(cathode), Av=104 and 1.4% 2nd H

Now I have changed the pentode to match the “classic WE91 values”, adjusted for an EF37A
90K @ plate
1K @ cathode = 2.6mA(cathode), Av=140 and 4.9% 2dn H

First impression is it sounds better….

I’m defiantly buying a scope; it will be interesting to see the new frequency response.
 
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