So I bought a Pro-ject Pre Box RS... (Valve suggestions?)


The Pre Box RS comes from the factory with Electro Harmonix 6922, on the output stage. All I have read about this pre has suggested a linear power supply upgrade and tube rolling gives
significantly better results, so the linear PSU is already done (19VDC from a HDPlex 200W).

I've already got some tubes I bought for my old old DAC (it's now 9 years old).
I have a pair of Amperex P.Q 6922 [VCM 163 tested], and a pair of
Phillips E88CC SQ [1109] with writing on the box [12500-12750 and 12400-12500 on the other box] What do those hand written numbers mean?

Anyway, which valves should I likely go with? (I am hoping for longevity as well as quality)



 
296b8550 a8d9 491e b6ed 711d1b5106c4rixthetrick
I think your tube pairs are probably very similar.  I think they both could have been made in the Amperex factory in Heerlen, Holland.  Here is a post I made in a similar thread. Check out the Phillips tube code pdf and if that doesn’t help let me know:

I think the Phillips/Amperex tubes that people are recommending are tubes made in the Amperex factory at Heerlen, Holland. Phillips sold these tubes with many different labels. Phillips owned many tube factories, Amperex, Siemens, Mullard, Valvo and many more, and tubes made in one factory were often labeled with another factory’s "brand." Your Phillips Miniwatts could have been made at Heerlen.

You can tell a Heerlen, Holland tube by the left facing right triangle that is the first symbol in the bottom line of the etched tube code. You can read about these codes here:

https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf

Any tube you’re likely to come across these days would have the ’New’ Code, illustrated on page three, etched on the side of the tube.
Thanks tomcy6,
I'll check out the codes and see if I can translate them :-)
You have some. Try them.
The tube codes are easy, if you can read them. Sometimes they are faint or invisible.

Top line is three characters:

tube type, tube type, change code (model or version #)

Bottom line is three or four characters:

factory symbol, year (last digit), month (A - L), week of the month.

If the codes are legible, post them and we can decipher them.
The 12500-12750 and 12400-12500 numbers are the readings from a tube tester (in UMhos).   The tubes have 2 plates in each and those are the numbers for each plate.    Without looking up what the numbers should be these seem like well matched tubes.   Each plate in each tube is the same.  And the 2 tubes are close enough for me.
Thanks delkal,
I am learning from you guys.

tomcy6,
Phillips SQ
I can make out (looks almost etched in a faded silver/grey)
7LG (then under it)
What appears to be a right angled triangle, with the hypotenuse coming from down on the left, to it's apex on the longest of the other two sides which is vertical on the right, then 1F4. Both have exactly the same markings.

AMPEREX P.Q (PQ with two stars, one between the letters up top and in the bottom of the shield)
Amperex
6922
Made in USA (funny as I purchased both sets in Australia, seem I brought them home) in silver numerals "332" and also separately below in grey
7L8 (next line under it had me puzzled)
at first the symbol under it looked like a wagon wheel, but then I realised it was a circle with the pins for the valve, and then 3F to it's right.
Elsewhere  it also has in larger white print, what I thought was a faded 405,but is in fact using both as a reference clearly 105 with a strike through the middle of the 1's, kind of like the French do with sevens. Maybe it is a 7?
With the shaft being vertical, or parallel with the 05, not at all angled to the right like a seven though.

Hope that's not too cryptic?
Thank you tomcy6




 
I think we can figure out what you’ve got. First the 7L means you’ve got two 6922s. You can find that code on page 13 of the pdf. Many changes were made to 6922s over their production life so this is reflected in the change codes of 8 and G. Letters were sometimes used when they went past 9 versions of the tube.

The first tube was made in Heerlen, the triangle indicates that. The next 3 characters give the date it was made, 1F4. I think it was probably 1971 because they started using the 3 character date code in 1962 or 3. The F is for June, the 6th letter of the alphabet for the 6th month of the year and the 4 means it was made in the fourth week of June. They weren’t as precise about dates as we are in the digital age.
The second tube I think was made in the US.  Phillips bought a factory in New York to be able to sell to the US military, who wanted their tubes to be made in America.  At least some of them, they also bought foreign made tubes.  I think the factory code is an asterisk *, which indicates the Amperex factory in NY.  You can find these factory symbols on page 5 of the pdf.  I think it was made in June of 1963.  More detail about the labels and construction could nail down the dates.
Heerlen tubes are usually described as having a lively sound and especially good in the midrange.  The American Amperex are also considered very good tubes, maybe a little more subdued than their Dutch brethren.

These are just generalizations though, and the only way to tell how they'll sound to you, in your system, is to try them out.  Differences may be subtle, but both pairs are considered very good tubes, so roll them in and enjoy!
I am still burning it in, as it came from factory.. It turned really muddy, but I am leaving a signal run through it, even if not at usual listening levels.
Currently it is either sounding better than it was out of the box or my audible memory is shot (left myself wide open, even chambered the bullet). I'll tube roll after burn in is completed.. a few hundred hours aught to do it? Should be about a fortnight, or so.

Thank you for so much information, much appreciated.


tomcy6
I'm flying back to visit family in Australia, and while I'm gone I was seriously considering cryo treating my speaker cables and interconnects.
Should I send the valves in with it? Had any experience with doing that?
No I don't.  Can't help you there.