PrimaLuna preamps. Use of 5R4GY tubes instead of 5AR4 / GZ34. Yes or no?

From the PrimaLuna website...

"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.".

I do not know what to think. They expressly advise the replacement of the 5AR4 / GZ34 with the 5R4GY.

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.

Hi TubeGB
so you had no problem using the 5R4GY instead of the 5AR4 / GZ34 on the Prologue 3.
Have you used them for a long time?
What improvements did you perceive?

yukio:
I have used them (Philips 5R4GYS) for several years now. Improvements are a little more warmth on the top end and a small increase in sound stage width.
I failed to mention the Philips tube is substantially taller than the stock 5AR4 tube and when in position you will no longer be able to use the tube cage.
Please note again that as a general rule, it's not a good idea to deviate from a 5AR4 tube and it remains a good idea to consult with Upscale Audio.

He's saying 5R4GYS not 5R4GY.....

Read this in case you're interested in more detail:
https://www.diyaudio.com/forums/tubes-valves/67523-5r4-gy-5ar4.html