Sunday, October 28, 2018

Tubes for Drake 

Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang  ----------------------------------------------------------------------  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 connectedinternally 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 tocathode 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  ----------------------------------------------------------------------  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!..."    ***************************************    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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Saturday, October 27, 2018


          

        










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Friday, October 12, 2018


          

        

















Sun is out at dunkin donuts 
  









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Tuesday, October 02, 2018


          

        










Rainbowish left side











  









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