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

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.