Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Eddy -
Nope, no cigar.......
NO modifications are needed to either the T-4(any) or the TR-4(any) to
use the 6GJ5s.
Pin 3 in the Drake 4 Line transmitters is the cathode of the final
tubes. Pin 8 in the transmitters is grounded at the socket.
With 6JB6s, K is connected internally to Pin 3, and G3 is connected
internally to Pin 8.
With 6GJ5s, K AND G3 are connected internally to Pin 3, AND there is
_NO_ connection to Pin 8.
So everything works the same, except G3 is connected directly to K
rather than via a 15 ohm and 3.3 ohm resistor.
The only difference is the interelectrode capacitance, which is small
enough (0.5 pF) that the neutralization circuit is able to take care of it.
NOTE: RCA Tube Manual for Class A Operation states "G3 connected to
cathode at socket".
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
EP Swynar wrote:
"EP Swynar" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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On Sunday 20th January, Garey wrote...
"...True, the G3 is brought out to Pin 8 in the 6JB6,
and that socket pin IS grounded in the T-4... However, in the 6GJ5 G3 is
brought internally to the cathode Pin _3_. There is NO connection to Pin 8
in the 6GJ5. Simple!..."
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Hi Garey,
I think I'm beginning to understand all this, at last...!
What's been missing all along here, is the mandatory execution --- right
from the get-go --- of TWO crucial operations, i.e.:
(1) The wire from pin #8 to chassis ground at the final amplifier sockets in
the T4X must first be snipped, and,
(2) A new wire has to be added, jumpering pin #3 to pin #8 at both sockets.
What will be accomplished thusly is the following:
(1) The pin #3 cathode "break-out" of the 6GJ5 will now effectively be at
the pin #8-cum-pin #3 of the T4X socket, and,
(2) For better or worse, the suppressor grids of the 6GJ5 tubes will be at
the exact same potential as the cathodes (NOTE: is that an especially
good --- or bad --- thing?).
Failure to first execute the "...nip & tuck" at the sockets will leave the
current meter reading "zero" all the time, and the finals will be "on"
constantly...correct?
I wonder if it wouldn't be simpler to just re-wire the filaments for 12.6
VAC, & a pair of 12JB6's, Hi Hi!
~73~ Eddy VE3CUI - VE3XZ
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