Substituting 6L6 for 6V6 in Hoffman Princeton Reverb

[acheld]

I recently built a Hoffman Princeton Reverb (no Tremolo).  It works fine.  https://el34world.com/Hoffman/files/Hoffman_PrincetonReverb_NoTremolo.pdf

Hammond 290AX for PT,  and the OT is Hammond 1760E -  designed for 8500ohms primary, and with 4,8, and 16ohm secondaries.

I have a bunch of 5881 tubes lying around, and got to wondering if I could safely substitute the 5881 tubes for the 6V6GCs that are in place?  I know the 6L6 tubes expect a lower primary resistance from the OT, but how much difference would that make?    If I used the 4ohm tap with an 8 ohm speaker, seems like the OT primary resistance would be higher than what the 5881s expect, right?  Is there a way of safely doing this?

My reason for asking is primarily hypothetical.   I just had some 6V6 tubes fail in a DR, and have now used up my stash of extra 6V6s.  But I've always wondered if you could sub in a 6L6 (or 5881) for a 6V6.  Obviously with re-biasing . . .    This particular amp is solely used for practice in the home, never pegged, and I don't need more power.   

[66Strat]

An 8 ohm speaker in the 4 ohm jack will result in a reflected impedance of 17k. That makes the mismatch worse. An 8 ohm speaker in the 16 ohm jack will result in a reflected impedance of 4.25K. The 290AX is a bit undersized current wise for 6l6/5881 tubes IMO.
https://www.hammfg.com/files/parts/pdf/290AX.pdf

[tubeswell]

6L6 and 5881 both have 900mA filaments (6V6 is 450mA). 6L6s/5881s are designed to run hotter to get more power outputs and therefore are capable of producing more plate current (and are designed to deliver this), and have different bias voltage requirements accordingly.  Provided your PT heater winding is appropriately rated, and your bias voltage supply is sufficient to ensure lower than typical plate current, you can run 6L6/5881s in that amp, and you can even run them as you would run 12W tubes (by biasing them cooler) and into a higher load resistance, but you won’t get any increased output power, and because the bias voltage is likely to need to be higher (to keep the plate current from overpowering the OT), the lower signal going into each output tube grid will suppress the onset of Class B operation (a and assuming the PI output signal is not able to be increased), thus the amp will run cleaner, and at a lower power output, and is likely to sound different/ more ‘sterile’.