[Amps] feeding the input

[peter.chadwick at Zarlink.Com]

Carl was asking about feedback resistors in cathode/filament circuits.

The answer it that it seems to vary. The Mullard data sheet for the QY3-125
(which is basically a 6151/ 4-125, as opposed to 4D21/4-125  - the
difference is that the 6151 doesn't have the metal base shell)) says that
RF return connections should go to pin 1. The QY4-400 ( a 4-400) has no
restrictions, although it's basically the same sort of device. The
QY4-250/6152 also suggests returns to pin 1 on early data sheets.

The Philips version of the QY4-250 (QB3.5/750) says nothing about filament
returns but says that both screen grid pins should be used to equalise the
currents.

With both QY4-250 and 4-250A's,  I have resistors in both sides. They have
series caps (old fashioned molded mica) of 0.01mFd so that I don't heat the
resistors with filament current.

I guess this probably doesn't help too much - it seems it's 'pays your
money and takes your choice' matter.

73

Peter G3RZP