[Milsurplus] 6K4

[Ray Fantini]

I have been working on a Russian military receiver that uses a tube
called a 6K4. This tube in no way resembles the US version of a 6K4, it
appears to be a remote cut off pentode maybe the Russian equal of a 6SK7
The tube is a octal base and just about the same size as a 6SK7, except
only a tiny bit shorter. The tube is used in both RF and IF amplifier
circuits. the IF deck has been modified for 7 pin miniature tubes, and
they appear to be 6K4P tubes. 
Both the octal and seven pin miniature have the same number and not
having good Russian substitute guides several questions come up. First,
can the 6K4 octal be replaced directly by a 6K4P mini? Second, the only
tube base diagram I have found for the 6K4P shows it as a directly
heated cathode where the octal one was indirectly heated, yet I am lead
to think that the 6K4P will directly replace a 6BA6 and I always thought
a 6BA6 has a indirectly heated cathode? and last but not least, will the
6BA6 directly replace a 6SK7? If the Russian 6K4 is a 6SK7, and the
receiver was modified to use a 6K4P that is the same as a 6BA6 will the
tubes have the same characteristic and respond the same way in regards
to AVC control? I can see that their are some small differences in the
capacitance but don't see that as any big issue. I do have to replace a
couple of the IF tubes and do not know if I should go with the Russian
6K4P that I will have to buy or just stuff America 6BA6 tubes in their.
Ray Fantini KA3EKH