wrote:
Antonio Vernucci ha scritto:

I am restoring an "old" drake TR-6, I just noticed a 100 ohm resistor
connected between pin 1 and pin 7 of
the three 6JB6 finals. I understand these two pins are both connected
internally to the screen grid, so
Looking to the schematic diagram, that resistors are in series to the screen, so originally they could not be shorted by the tube.

I have the original schematic and it shows the 100 ohm resistor between
pin 1 and 7, you can find the
TR6 schematic at the following link (look at the last page of part 2):
ftp://bama.sbc.edu/downloads/drake/tr6/
You can see the 100 ohm resistor between pin 1 and 7 of each final tube
and the additional 100 ohm
in series connected at pin 7 of each tube, which isn't actually correct
as in my unit only one tube
is connected this way, the other two are connected to pin 1.

Pin 1 and pin 7 probably connect to opposite sides of the screen. Perhaps
the inductance of this connection creates an opportunity for a VHF parasitic
resonance, and the 100 ohm resistor is there to dampen it out?

-Chuck

Hello,

Chuck Harris wrote:


Pin 1 and pin 7 probably connect to opposite sides of the screen. Perhaps
the inductance of this connection creates an opportunity for a VHF parasitic
resonance, and the 100 ohm resistor is there to dampen it out?

Yes, this can be the reason, thanks for the hint!
Probably is anyway a good thing to add similar resistors in a home made
tube linear.

73

Francesco IS0FKQ