Can 5AR4 be replaced by 5U4G or 274B?

I own Pilot SA232.

Thanks

Sorry, but I'm not familiar with that particular circuit.

WOW !!!!! Pilot SA232 is a super great sounding amp. Please e-mail me when you don't want it !!!!

Oddly enough, the Prompt tube substation handbook says 5AR4 is sub for 5U4G, but not the other way around.

For 5AR4, subs listed are GZ34, 52KU, 54KU, GZ30, GZ32, GZ33, GZ34, GZ37, R52, U54 and U77.

Still I would try to find an old tube guy that knows this piece and can verify tube subs before proceeding. It would be a shame to ruin it.

Its really not odd that tube X can be universally substituted for Y and not the other way around. Tube X may be be able to handle more voltage or current than Y so it can deal with whatever Y had to handle, but Y can't handle what X can. However, Y could be substituted for X in some circuits if that circuit doesn't exceed its limits. You would need to know more about the circuit and the tubes to determine that. There are other parameters such as inter-electrode capacitance, plate resistance, filament current, etc. that could keep a tube from working well in one circuit when it would substitute just fine in another.

I'm sorry I can't answer the original question as I'm on the road and my tube manuals are at home.