La Radiotechnique 12AX7S info.

[CageyH]

I have just bought an RT 12AX7S valve, and underneath the 12AX7S and the letters HF.
Any idea what these mean?

[Barry]

Guessing the "F" means it was made in Suresnes, France, and the "H" denotes August. As to the year (> 1955), you will need to find a number.

https://tubemaze.info/deciphering-european-tube-date-codes/

[Marco]

Not sure what the 'HF' is, Kevin, but they're FAB tubes! Much did they set you back?:)

Marco.

[CageyH]

29494

I bought this one for €55 posted.

Thanks for the info. I thought the code on RT was FRS for Suresnes? There is a 4 digit code, which I assume is the date, something like 6332 from memory.
I also have a nice silver plate Mazda 12AX7S on the way, a 5* version, which again is an -H.

[Barry]

If the date code is 6332, then the valve was manufactured in the 32nd week of 1963. So anytime between 9 - 15 August 1963.

Under the CV (Common Valve) system of notation, a group of letters were used to denote where the valve was pumped out. For La Radiotechnique the following two letter codes applied:

DN - Caen
JK -Suresne

https://www.valvecollector.uk/cv-valves.htm

[Marco]

Nice one, Kevin. These are the ones I got, which are slightly older: https://theartofsound.net/forum/showthread.php?49050-New-Valves-for-phono-stage&p=841160#post841160

Superb sounding tubes. It took a NOS Mullard (early 60s issue) M8137 box-plate to oust it, and that one cost me £150, but can often go for nearly £300 a piece!:eek:

Marco.

[CageyH]

I received one of the valves today.
It has the three magic letters on it - FRS, so it looks like HF is a batch code, or similar.

[CageyH]

Nice one, Kevin. These are the ones I got, which are slightly older: https://theartofsound.net/forum/showthread.php?49050-New-Valves-for-phono-stage&p=841160#post841160

Superb sounding tubes. It took a NOS Mullard (early 60s issue) M8137 box-plate to oust it, and that one cost me £150, but can often go for nearly £300 a piece!:eek:

Marco.

Out of interest, where did you get yours from?

[Marco]

Now you're asking, mate. It was a while ago. Don't think it was ebay, or a private individual, probably a specialist tube seller. They're pretty rare,

I only ever buy genuine NOS (or NIB) valves, which are balanced (or balanced as closely as possible), and thus have been measured by someone with the necessary testing equipment, as you'll see evidence of with the stickers:)

I don't buy random untested valves, as they tend to be unreliable.

Marco.

P.S I should clarify that the NIB valves I buy are always 'sold as seen', therefore untested, and NOS ones are only such, as far as only having been 'used' once for testing/measurement purposes, not in audio equipment.

[CageyH]

Now you're asking, mate. It was a while ago. Don't think it was ebay, or a private individual, probably a specialist tube seller. They're pretty rare,

I only ever buy genuine NOS (or NIB) valves, which are balanced (or balanced as closely as possible), and thus have been measured by someone with the necessary testing equipment, as you'll see evidence of with the stickers:)

I don't buy random untested valves, as they tend to be unreliable.

Marco.

I guess it depends where you look.
I am sure this guy http://www.electrotubes.com/index-en.html would have something? He seems to have a good reputation on the French forums. He does not list balanced/matched pairs of the RTs, but I am sure he could find something.

If I didn’t have a nice Tungsram Foil getter ECC83, a Mazda silver plate 12AX7s and another RT on the way, I would be speaking to him.
Not sure what the Brexit implications are though, as I am not sure if he is a registered business, as I have never used him.

He certainly has some interesting valves available though.

[Marco]

Thanks for the link. Looks interesting:)

However, he'll only be able to test valves if he has a proper valve tester and knows how to use it. That may be the case, but it may not. If you're dealing with him again, I'd ask. Even if he has one and knows how to use it, however, he may be reluctant to go through all his stock, measure and find matched pairs.

Depends on both him and his business. However, I can say with some certainty that there's a BIG difference, in both sound and potentially good reliability, when comparing matched (balanced, which is a different thing again) valves with the opposite, especially in critical applications such as phono stages!

Marco.