Don't ask about the printing. It' actually normal on the tube.
Photobucket kept flipping the pictures when I uploaded them
so I loaded them upside down so they would flip right side up and this was the result.


Now I had also acquired 40 NIB National branded 5751 tubes a year and a half or so ago from a customer of mine. They had used them as spare parts in old equipment but hadn't needed any in a long time and were looking to liquidate a bunch of dead stock. When I checked their records I saw that they were part of a 50 pc buy they did in '93. They still had all 50 and decided to keep 10 just in case and sold me 40. I had a few of them tested on a high end computerized tester and the guy I sent them to told me that the test results indicated that they were high gain 12AX7's and that they were likely just labeled as 5751's. I sold off most of that lot to Doug's Tubes and traded some with dudes on forums. I had tried those in a few of my amps and didn't really like them in the amps I tested them in so I didn't really care to hold onto many but kept a few for utility use. Anyway, I compared one of those with this Beijing tube and I'll be damned if it isn't identical in every way.


Anyhow...I pulled the access cover off the back of my 6505+ head and and swapped some glass to see if they are as good as I had read about in high gain amps.
I had been running this Philips labeled Mullard in V1...

and had previously tried a lot of different tubes in V2. I had a ANOS Sylvania in it for a while then picked up a little '60s Danaelectro amp that had an IEC Mullard in it so I slapped that in there. That made the lead channel a little dark and fizzy. I didn't bother to test it and it may have been a little weak so I put in this GE 5751 which seemed to help me balance channel 1 & 2 well so I left it in.

So out they both came and I stuck in the Chinese glass. At first I thought, not much difference....why waste the vintage tubes, I'll leave these in. Then I cranked it.



HOLY SMOKES!!! Now I know why guys love these in high gain amps. I put the 5751 in V1 and the 12AX7A in V2 then took another 5751 and tried that vs the 12AX7A. The 12AX7A version has slightly more gain than the 5751, not a lot...just a bit. The voice is the same and the volume is the same too. They sound great in my 6505+. I tried a brand new TAD high grade 7025 to compare a better grade Shuguan against the 5751 and the TAD sounded anemic by comparison. And to think I had 40 of these and let almost all of them go. Oh well. I didn't have an amp they got along with at the time. I may have to go back and get a few more of them.