Eimac y-383 socket for the 4cx3000A

$350.00

Because the Eimac Y-383 (SK-1400 series) and the 4CX3000A use a coaxial breechblock base rather than traditional numbered pins, the connections are arranged as concentric metal rings moving outward from the center post.

Coaxial Base Layout (Bottom View)

Looking directly at the bottom of the 4CX3000A tube (or down into the top of the Y-383 socket), the contacts form a bullseye pattern from inside to outside:

text

          . - ~ ~ ~ - .
      . '   . - ~ - .   ' .
    /     /   . - .   \     \

   |     |   | (F) |   |     |  <-- Center Post: Filament (F)
   |     |    ' - '    |     |  <-- Inner Ring:  Filament / Cathode (F / K)
    \     \   ' - '   /     /   <-- Middle Ring: Control Grid (G1)
      . '   ' - ~ - '   ' .     <-- Outer Flange: Screen Grid (G2) + Breechblock Tabs
          ' - ~ ~ ~ - '

Use code with caution.

Note on the Anode (Plate): The Plate (P) is not located on the base. It connects at the very top of the tube via a heavy copper anode strap or clamp around the cooling fins.

Contact & Terminal Mapping

When wiring the underside of the Y-383 socket, each concentric ring routes to a specific terminal ring or lug underneath the chassis deck:

Position (Inside to Out)	Tube Element	Symbol	Socket Terminal Location	Electrical Notes
1. Center Post	Filament (Side A)	F	Center collet / terminal at the very bottom axis of the socket.	9.0 V AC/DC (41.5 A). Heavy gauge wiring required.
2. Inner Ring	Filament / Cathode (Side B)	F / K	Innermost circular metal ring surrounding the center post.	Directly heated thoriated-tungsten filament; also acts as the cathode return.
3. Middle Ring	Control Grid	G1	Middle concentric ring separated from the inner ring by ceramic insulation.	RF drive input and negative DC bias (-100 V to -250 V typical).
4. Outer Flange	Screen Grid	G2	Outermost locking breechblock ring (with 3 or 4 twist-lock tabs).	Connects to the built-in screen bypass capacitor ring and +DC screen supply (up to 1,000 V).
Top of Tube	Anode (Plate)	P	External to socket (clamped to top radiator fins).	High-voltage DC plate supply (up to 6,000–7,000 V) + RF output tank.

Socket Insertion & Locking

Breechblock Alignment: Line up the locking tabs on the tube's outer Screen Grid (G2) flange with the cutouts in the top rim of the Y-383 socket.
Twist-Lock Engagement: Press the tube straight down into the spring fingerstock contacts and rotate clockwise slightly until the tabs lock beneath the socket lip.
Verification: You can verify the underside terminals on your Y-383 with a continuity tester by probing from each top fingerstock ring to its corresponding solder tab or screw terminal on the bottom of the socket assembly (see the Eimac 8169 / 4CX3000A Datasheet for exact mechanical base dimensions).

If you have a photo or part number of the transmitter (such as a Harris MW-5 schematic) or want to check how the screen bypass capacitor is wired on your specific Y-383, let me know and I can help map the exact circuit connections.