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)



 
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Showing 6 responses by tomcy6

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.
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.
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.
No I don't.  Can't help you there.
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!
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.