Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on September 02, 2012, 03:42:28 pm
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I have tried to find a clear definition for a triode connection
and have noticed that there are many different practices used. What is essential
in triode connection and how it should be done?
/Leevi
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tie screen grid (g2) to plate with a 100R resistor. as usually done with pentode configuration, tie suppressor grid (g3) to cathode or ground, whichever you prefer; usually it's easiest to strap g3 to cathode at the socket.
--DL
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I have tried to find a clear definition for a triode connection ...
Screen is tied to the plate, sometimes through a resistor as DL suggested.
When a triode is used, plate current varies with plate voltage. When a pentode's screen is held at a fixed voltage, plate current changes very little with changing plate voltage, and you get characteristic pentode curves.
When a pentode's screen is tied to the plate, the screen voltage varies when plate voltage varies; this causes plate current to vary, so you have the same end result as a triode with the same plate/control grid/cathode geometry as the pentode. This means that different pentodes, when strapped as a triode, will offer differing mu, Gm and internal plate resistance.
Mu from g1 to g2 will be the mu the tube will exhibit when operated in triode mode.
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Thanks for the clarification guys!
Leevi