4P1L tubes for the Smash

[airdronian]

I'm not familiar with the 4P1L, and a quick search didn't seem to uncover many sources.

Were these strictly a Russian manufactured tube ? 

Roughly how many hours of service could one expect out of these, implemented as they are in the Smash ?

Any info on these tubes would be appreciated.

[mcandmar]

I used them in an old tube amp to replace a pair of Chinese 4P1S tubes, i'm not aware of any other equivalents other than the Russian 4P1L.  Russian versions were the better of the two.

[Paul Birkeland]

Were these strictly a Russian manufactured tube ? 

Roughly how many hours of service could one expect out of these, implemented as they are in the Smash ?

Any info on these tubes would be appreciated.

There may be an old Telefunken tube that served as the basis for the 4P1L, but I'm not finding a reference to that in a quick search. 

I don't know how many hours you could get out of one.  It might take several years of constant use to wear out a pair of tubes, and in that instance you wouldn't have the wear and tear from power cycling, so the number wouldn't be that helpful. 

[Paully]

Makes me wonder if there are other tubes that could be used with a simple pin-out change and maybe a resistor like the FPIII...  6SN7, etc...?

[Paul Birkeland]

Sure, there are a crap ton of tubes that could be built into the chassis to function as a preamp. 

The tough part is that few of them will be directly heated with adequate beef to function as a preamp tube without an output transformer, and of those that are that beefy, the filament requirements may be unreasonable.