yukio:
I
have used the Philips 5R4GYS in my PrimaLuna ProLogue 3 with great success/results.
The Philips tubes were purchased from Upscale Audio. They are the only tubes
tried in this position other than the stock PrimaLuna 5AR4’s.
As
others have mentioned I would consider it a bad idea deviating from a 5AR4 type
tube, unless recommended by PrimaLuna/Upscale Audio.
From
the PrimaLuna Tube Rolling Page:
The
5AR4's used in our preamplifiers are considered to be fantastic. It is as close
as you are going to get to a classic Mullard. We have found that the Mullard
and Gold Lion Russian re-issues are not as dependable in PrimaLuna preamps, so
it’s best to stay stock when it comes to current production 5AR4’s.
Do NOT use 5V4/GZ32 as they may fail and cause damage not covered by
warranty.
There is a vintage tube that is quite popular called a
Philips 5R4GYS. Very cool looking tube that lasts a long time. It has a
slightly warmer presentation, if you need that. Read the reviews from other
users. A lot of people like it, but if your speakers don't have enough
top end, it may not be a good idea.