[R-390] Done to death, delete at will: 6DC6 surrogates

[David Wise]

I picked the word "surrogate" with care.  These are not
substitutes.  They are enough to keep you on the air
while you look for a 6DC6.

For reference:

6DC6 (5500, 12.5V=3D50umho)

RC-29 is inconsistent about cutoff ratings,
some are at various currents, others at
various transconductances.

A couple of these are from memory.  Others
don't have any cutoff data.  Except for the 6AS6,
I didn't check max ratings.  Remember, it's
temporary and who cares if you burn it up.
A lot of these are TV tubes, so if you have
a box of pulls, odds are you have a few.
Some of these didn't exist in 1952; I bet
they'd have picked the 6GM6 or 6DE6
for example.

Out of the list below, I tried a very weak 6BZ6,
a 6EW6, and a 6HZ6.  All worked, but of course
not as well as the real thing.  I didn't check
sensitivity, IP3, cross-modulation, or what-have-you.
Don't expect the same carrier readings in any case,
because the AGC is different.

I worried about oscillation with the 6EW6,
but I didn't see any.

7CM pinout (same as 6DC6):

6AS6 (way over max ratings)
6BH6 (low gm, too sharp)
6BJ6 (low gm, too remote)
6BZ6 (8000, 19V=3D50umho.  Runner-up to 6DC6 in Cost Reduction Report.)
6CB6 (8000, 6.5V=3D20uA)
6CF6 same as 6CB6
6DE6 (8000, 9V=3D20uA)
6DK6 (9800, 6.5V=3D20uA.  Used in large numbers in Tek 500-series =
scopes.)
8136 same as 6DK6
6EW6 (14000, 3.5V=3D20uA)
6GM6 (13000, 15V=3D60umho)
6JH6 (8000, 19V=3D50umho)
6JK6 (15000)

7EN pinout (same except internal shield connected to cathode instead of =
G3):

6DT6
6GX6
6GY6
6HZ6

These tubes are designed so G3 can be used as a second control grid.  =
All
have lower gm than the 6DC6.  I didn't write down their cutoffs.  I =
think they're
all sharp.

Some RF decks have pins 2 and 7 wired together.  These decks
can also use a slew of tubes with the 7BK pinout, which includes
6AH6, 6AG5, 6BA6, and 6BC5, and another pinout I forget which,
which is like 7BK but with K and G3 swapped.

73,
Dave Wise