[AMRadio] 807's triode connection question...

[Donald Chester]

>From: <ka1iic at prexar.com>
>
>...I've been looking up all the info I can get about using 807's in triode
>connection....

>First off the older ARRL handbooks show connecting the grid to the screen
>through a 20k ohm resistor and driving the screen...

That makes the tube act like a high-mu zero-bias class-B triode.

>
>Another publication shows connecting the screen to the plate directly and
>driving the grid as you normally would...

>And case three shows connecting the screen to the plate through a 100 ohm
>resistor and driving the grid as per the norm...

That makes it act as a low-mu triode, and reduces the plate resistance.  
This would be mose useful to drive a loudspeaker or to use to drive a 
class-B amplifier stage.  It would require considerable negative grid bias 
and would be less desirable as a class-B amplifier.

The 100 ohm resistor could be to stop parasitics or to reduce the "dynatron" 
effect, in which there is a kink in the characteristic curve that results in 
a negative resistance effect, and can cause intermittent oscillation and 
distortion over part of the audio waveform.

Don K4KYV

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