COLIN LAMB wrote:
Hi Tony:

My 1936 Radio Handbook gives the following information:

"Grid-leak bias is quite flexible and more or less automatically adjusts
itself with any variation in RF excitation. The value of grid-leak resistor
is not particularly critical because the DC grid current usually decreases
as the grid-leak resistance increases, theeby keeping the product of the two
more or less constant for a given amount of RF excitation. Hence, the value
of the grid-leak resistance can vary from one-half to two times the optimum
value, a ration of four to one, without materially affecting the negative DC
bias voltages actually applied to the grid of the amplifier tube.

One of the disadvantages of grid-leak bias is that the bias voltage is
proportioonal to the RF excitation, thus precluding the use in grid
modulated or linear amlifiers, whose bias must be supplied from a
well-regulated voltage source so that the bias voltage is independent of
grid current."

So, I guess the answer is "use whatever value that makes the tube happy".

73, Colin K7FM


Actually the value of the grid leak bias resistor used in a class C
amplifier is going to be a function of the available peak RF voltage
being supplied by the driver stage, and the required grid drive / bias
voltage of the final. The maximum allowed grid current rating of the
final tube must not be exceeded either. If you look at some classical
ham transmitter circuits the grid resistor value varied quite a bit.
For the 807 tube a typical value was 15k (as recommended by RCA) but
where drive current was limited (such as on ten meters driven by a
quadrupler from 40) a 22k or higher value was common.

"Kenneth Scharf" ha scritto nel messaggio
...
COLIN LAMB wrote:
Hi Tony:

My 1936 Radio Handbook gives the following information:

"Grid-leak bias is quite flexible and more or less automatically adjusts
itself with any variation in RF excitation. The value of grid-leak resistor
is not particularly critical because the DC grid current usually decreases as
the grid-leak resistance increases, theeby keeping the product of the two
more or less constant for a given amount of RF excitation. Hence, the value
of the grid-leak resistance can vary from one-half to two times the optimum
value, a ration of four to one, without materially affecting the negative DC
bias voltages actually applied to the grid of the amplifier tube.

One of the disadvantages of grid-leak bias is that the bias voltage is
proportioonal to the RF excitation, thus precluding the use in grid modulated
or linear amlifiers, whose bias must be supplied from a well-regulated
voltage source so that the bias voltage is independent of grid current."

So, I guess the answer is "use whatever value that makes the tube happy".

73, Colin K7FM
Actually the value of the grid leak bias resistor used in a class C amplifier
is going to be a function of the available peak RF voltage being supplied by
the driver stage, and the required grid drive / bias voltage of the final.
The maximum allowed grid current rating of the final tube must not be exceeded
either. If you look at some classical ham transmitter circuits the grid
resistor value varied quite a bit. For the 807 tube a typical value was 15k
(as recommended by RCA) but where drive current was limited (such as on ten
meters driven by a quadrupler from 40) a 22k or higher value was common.

Thanks both for the quote and the comments.

73

Tony I0JX