The Heath SB-220 used an rf choke to ground the grid, bypassed by 3 x 200 pf
capacitors. Interestingly, the Drake L4 amplifier used an rf choke to
ground the grid, bypassed by 3 x 200 pf capacitors. That suggests that one
manufacturer copied the other - or that both manufacturers copied someone
else.
It has been stated that Bill Orr came up with the idea, so it is possible
both companies figured it was magical and copied it without understanding
it. However, my 22nd edition of the Radio Handbook (first printing 1981),
edited by Bill Orr, has a 2 x 3-500 amplifier construction article and the
grids are grounded directly. If he was the one that suggested it, perhaps
he was smarter by the time this edition was published.
This is a lucky engineer, when you design something wrong and it still works
40 years later.
73, Colin K7FM
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|