Wireless World
Base Diagram Explanation
The following pages of valve-base diagrams show all the sets of base
connections that are necessary to cover the valves listed in the tables
of characteristics. They are grouped into sections according to the base
designations (B7G, B8A, B9A, etc.), and within a section each diagram
has a code number to the bottom right of it which identifies that
particular set of connections.
Thus to find the base connections of a valve listed in the tables, it is
first of all necessary to look up the designation in the "Base Type"
column. which gives the right section of diagrams, and then the number
in the "Base Ref." column, which gives the code number of a particular
diagram in that section' For example, to obtain the. connections of the
6F33 valve, one would have to turn to the section of diagrams headed
"B7G" and then look for diagram No.21.
British and American bases which are not interchangeable are given their
standard designations. American bases which are interchangeable with
British are in some cases given the British designations. Thus, B7G is
used to cover both British and American miniature 7-pin bases and B9A for
the British 9-pin and the American Noval. The term International Octal
(IO) is used to cover both the British B8-O designation and the American
standard Octal.
The designation B8B is now out of date; however, it is used here to cover
the British B8G base and the American Loctal and Lock-in types. None of
these is identical but the differences are so slight that all will fit
the same valveholder. The differences are concerned chiefly with minor
points about the spigot material, spigot taper and so on.
Three British bases are given arbitrary designations because there are no
standard ones short enough. They are the small 4- and 5-pin (Sm4 and Sm5)
bases fitted to some hearing-aid valves and the side-contact base (Ct8)
of continental origin and now obsolete.
Care must be taken to distinguish between the IO and MO bases,
particularly as the latter is sometimes called the British Octal and is
now designated B8-MO. The two differ in pin spacing and in spigot size
and are not interchangeable. The MO is used by one manufacturer only and
has the larger diameter spigot of the two.
The abbreviations used for the connections are substantially in
accordance with British Standards Specification BS1409. Some additional
abbreviations, however, have had to be introduced.
Similar electrodes which operate in turn on the same electron stream are
numbered in order from the cathode, the numbers being appended as
subscripts to the electrode symbols.
Similar electrode systems in multiple valves are distinguished by a
single tick (') for the first electrode system, by a double tick (") for
the second, and so on, the ticks being appended to the appropriate
electrode symbols.
Dissimilar electrode systems in multiple valves are distinguished by
additional letter subscripts appended to the symbols for the less complex
electrode structures.
A number against a pin indicates that it is joined internally to the pin
of that number.
Where more than one electrode is joined internally to the same pin only
the electrode of major importance is usually designated. Thus, the
suppressor grid of a pentode is not always shown when it is joined
internally to cathode or filament negative. An exception is made when it
may be important to the user to know precisely which electrodes are
joined together.
No distinction is normally made between valves with and without external
metal screens. The base connections show an "M" for such a screen in
cases where all or only some valves have it, but others with the same
code reference may have no such screen or an internal screen. The "M"
pin should, therefore, normally be earthed.
Some valves have the suffix "Met" to their numbers arid are listed
separately but generally they are equivalent to the valves without such
a suffix.
Abbreviations for Valve-base Connections
MAIN SYMBOLS
a = anode
bp = beam plates
ce = control electrode
f = filament
g = grid
h = heater
ic = internal connection (external connections must
not be made to a pin so designated)
jp = jumper
k = cathode
M = external conducting coating
m = internal conducting coating
p = priming electrode
r = resistance
s = internal shield.
st = spark trap
t = target
tr = trigger
TC = top cap
SC = side cap
SUBSCRIPT SYMBOLS
d = diode
p = pentode
r = rectifier
t = triode
tap = filament or heater tapping
(+) = positive
(-) = negative
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