Sylvania 12AX7s ID?

[Jeff R]

Latest eBay purchase just arrived ...

Seller said they test 100 percent. Three appear to have been never used at all.

I don't really know a lot about NOS tubes. I got them because the price was very nice (cheaper than current Mesa-stamped Chinese preamp tubes), and the old Sylvania tube that's in V1 of my Mark III right leaves current stuff absolutely in the dust.

On the four tubes I got today, the plates are gray in color, and the getters inside the top are square shaped(?). Any idea how old are they?

 

[stokes]

Quite often there is some sort of date code on the box somewhere.Usually on one of the boxtop flaps.

 

[Timbre Wolf]

Jeff -

Those short gray-plate/square-getter Sylvania 12AX7 were only made for one year. Sylvania began their production in late 1956, and switched over to their long gray-plate version in late 1958.

Prior to the short, gray-plate, they made a short, black-plate version of 12AX7 that appears nearly identical, except for the shiny black plates. Other visual clues, to help identify both of these fine tubes, include short plates that look like 5751-style, and a glass tip that appears pointier than any other 12AX7. Both mid-'50s short-plate 12AX7 break up earlier, with the black-plate having a somewhat brighter clarity. Being short-plate tubes makes them both less susceptible to microphonics.

Sylvania's earliest 12AX7 was a long black-plate, then they went to short-plates (black, then gray), then back to long-plates (gray).

Those tubes you got are excellent, if in new condition. The early-breakup quality makes me liken them to RFT's ECC83, but they're less murky-sounding for your cleans. A better RFT, in my opinion. Because of the early-breakup, I would advise using them judiciously, and not just loading up every 12AX7 position in your amp with them.

- Thom

 

[Jeff R]

Thanks for the great information, Thom. Advice heeded on the "use sparingly" suggestion - I found out quickly that just a V1 replacement was enough to make an unbelievable improvement in the tone of the amp - and that was after it was already drastically improved by a long-plate Sylvania in V1.

 

[Timbre Wolf]

Thanks for the great information, Thom. Advice heeded on the "use sparingly" suggestion - I found out quickly that just a V1 replacement was enough to make an unbelievable improvement in the tone of the amp - and that was after it was already drastically improved by a long-plate Sylvania in V1.

Glad to hear you're enjoying them. I certainly encourage experimentation - doesn't hurt. But you may end up with an overly-rich setup, that's not as satisfying as it could be if you select for each position separately. Personally, using my ears, I always end up with a collection of various tubes that differs, depending on the amp.

- Thom

 

[Jeff R]

Agreed, I'm just using the Sylvania in V1. V2 and V3 are Boogie-stamped Chinese tubes, a 12AX7 and a SPAX7 respectively. V4 and the phase inverter IIRC are Sovteks right now.