[Amps] Help with HP 428B Clip On Ammeter

[David C. Hallam]

I recently acquired a nonworking HP-428B.  The price was right, free.  I
downloaded a 428B manual from BAMA but find that HP introduced modifications
that are not covered in the earlier BAMA manual version.  Mine has a serial
number prefix 0995A.  It has tubes and discrete transistors mounted on a
printed circuit board, no point to point wiring.  One of the tubes is
missing and there is no identification of the tubes on the PC board, no tube
number or V-X reference to a BOM.  The socket is for a 9 pin miniature tube
and is located immediately to the center left of the power transformer.
It's not a rectifier as there is a SS diode FWB.

Can some one identify the tube for me and/or suggest where I might be able
to locate a manual that covers my version of the HP 428B?

David
KC2JD