5AR4 rectifier tube question

     Here's something you may find interesting.

     There are some Mullards compared, for plate structure, etc and the last two both have the 5 tooth, top mica.

      Just a way to close in on the valve's year, but: not nearly as important as the condition, strength and sound.

https://www.google.com/search?q=identifying+mullard+5ar4%2Fgz34&oq=identifying+mullard+5ar4%2Fgz34&aqs=chrome..69i57j33i160.14529j1j15&sourceid=chrome&ie=UTF-8#kpvalbx=_5wJeYqXzL7CO9PwPpqq18AQ15

I went through the same exercise with a Modwright Pre-Amp w/ outboard power supply.  After listening to a number of NOS options I ended up with a metal base.  It was expensive but had the most positive impact to SQ of any tweak i’ve done.   I think it was a ‘56 or ‘57.   

@rodman99999 thanks! I did a quick skim of the URL you posted & I quickly caught this from one of the people who answered on one of the forums:

The Mullard GZ34 has a hole in the guidepin and the upper micas have 5 teeth per side. On a new NOS Mullard the flashing extends down BEYOND the level of the mica.

so I am not sure what "the flashing" is referring to, but I am petty sure I must have 5 teeth per side. . . .

Some have four, some seven, but: forget the notches.

Not important!

How’s it sound?

Well, it sounded good tonight . . . but here is the thing--it was not sounding bad before, and I frequently confess to not possessing The Golden Ear (& I don’t intend any sarcasm whatsoever with that term). I seem to hear incremental changes when they get worse more than I do when they get better. When things get incrementally better, I seem to get more comfortable & relaxed . . . but the thing on that is: it takes a while for me to fully realize & appreciate that feeling. I am absolutely horrible at doing A/Bs (unless what I am comparing is just radically different), & therefore I hate doing A/Bs. It would be hard to A/B rectifier tubes in this pre, as it would require getting it down & then pulling the bottom cover off.

But: I did like the way everything felt tonight.

                                    Just relax and enjoy the music.

     Its a lot easier to obfuscate issues with a quick A/B comparison, than over the long term.   That, "comfortable and relaxed...feeling", in YOUR listening room, over the long term, is ALL that's important.

      Keep in mind: valves typically take something like 50 hrs of use, before they sound their best.    Some will claim such is a result of ones ears adjusting.   

      This is a verbatim quote, from a letter Brent Jessee sends, whenever one buys valves from him: 

                  "CARE AND FEEDING OF NEW TUBES: BREAK-IN
New tubes need a break-in period before they can fully exhibit their true sonic character when used in audio circuits. Preamp tubes especially benefit from a good break-in. This period may vary widely, but NOS vintage tubes usually need at least 48 hours of use, sometimes up to 100 hours. New current production tubes need 24-48 hours typically.
Good break-in can be accomplished by either leaving your tube unit turned on in a no-signal condition for 2 days, or you can just enjoy the tubes for several hours each evening and they will be broken in after several weeks. New tubes, especially NOS vintage tubes, may sound a bit edgy at first, but after the break-in period will mellow out and sound wonderful."

                                             Enjoy your jams!

 btw: That, "flashing" mentioned is the main component of a tube’s gettering system.

                                         Here’s some info:

                            https://en.wikipedia.org/wiki/Getter