[AMRadio] Re: Triode connecting 803's for a Modulator

ne1s ne1s at neandertech.com
Mon Apr 10 13:03:44 EDT 2006

Elaborating on Don's comment, the reason this is done with the 
triode-connected 807 is that if the control & screen grids were simply tied 
together, the control grids would be exceeding their maximum dissapation 
before the screens could be driven hard enough to provide reasonable output. 
We don't want to vaporize the control grids now, do we :>) I suspect this 
would hold true for other tetrodes & pentodes in a triode connection. 

I've used 6146s as modulators in the triode connection on a couple of 
occaisions. I feed audio to the screen grids only and just bias the control 
grid with a DC voltage to set it at the proper operating point. At lower 
plate voltages (say, <600V or so), the control grids can be tied directly to 
ground. At higher plate voltage, a few volts negative wrt cathode is all it 
takes. Screens are at DC ground in either case. 

Perhaps try something similar with the 803s? 


Donald Chester writes:
> I assume all three grids simply strapped together.  Is that correct? 
> In some circuits with triode-connected tetrodes, particularly the 807, the 
> screen grids are driven directly with the audio, and a resistor is placed 
> between the screen and control grids.

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