Tube synth diy

excuse my ignorance too..
but why do most of the circuits in Waveforms use a 6AG7 diode
connected, rather than just a regular diode tube?
Is there some advantage to using a pentode as a diode?



--- In tubesynthdiy@yahoogroups.com, "Fernando de Izuzquiza" <fdi@...>
wrote:
>
> In Files/Waveforms/ there are some interesting simple circuits using
a 6AG7 "diode 
> connected" (diode modulators, etc)
> 
> Does it mean those are passive circuits?
> No need to apply voltage even to heaters?
> 
> Excuse my ignorance...
>