Other Rectifier tubes Alternative for 5AR4

I have several components that it explicitly stated that I can use a variety of rectifiers in the same family: 5AR4, 5U4, 5Y4, 5Y3 ... etc.

i have a custom built 300B power amp based on the Luxman MQ-300. It uses 5AR4, but it doesn’t state I can put in other tubes. How safe is it to put in other rectifier tubes mentioned above?

Thanks in advance.
No. I mean that in your amp that quality won't make a difference. Cathode stripping is a phenomena of indirectly heated power tubes. Your power tubes are directly heated (the filament is the cathode literally) so cathode stripping is impossible.
Late to this thread. Just today, I spoke with the authorized Luxman warranty tech, Mike Garry, about replacing the 5AR4 with a 5UG4 in the MQ-300. He said do not do it. The amp's huge power supplies have an inrush that could be too much for a 5UG4. Or something like that. Glad I asked because I just bought an MQ-300 and I have a stash of nice 5UG4 that I would have tried in it.

Can it be confirmed that the LS100 will accommodate a coke bottle 5u4g in height inside the unit?


I can confirm that a 5U4G will *not* fit under the cover of a stock LS100. I believe Dan can provide a cover with a hole to accommodate taller rectifiers. I ran a 5U4 in that preamp for a long time, and I just kept the cover off. FWIW, my favorite in that preamp was the 6106, which is the same size as the 5AR4 so the cover will fit.