I can recommend the original Military Telefunken ecc801s made in the 60’s, this is clearly one the the best tubes of this type and extremely rare today. This is what i’ve been using with a great result with my tube amp. I bought mine (NOS) from The Tube Musseum NYC, those tubes are very expensive. Beware of the fake Telefunken tubes from ebay sellers!
Then for a few years i’ve been looking for something cheaper, but also outstanding quality. After a years of my research i found the Sylvania GOLD BRAND 12at7WA with gold pins (NOS) and was happy about it. Those tubes are also from the 60’s, great tubes and one of the best US made tubes of this type.
You can also looks for the vintage RCA tubes, but it was too late for me because i sold my tube amp, but still have some nice tubes.
One of the most interesting and extremely rare tubes are Japanese Matsushita 12AT7WA made in the 60’s (still have NOS quad). You can find a little info about those tubes on audioasylum forum in tubeasylum section whre all the tube freaks are posting, look for "bumby b" posts. The usability of that forum is awful !!! So i think it would be better if i will just post quites here to spread the lights.
***This is what i have in my notes saved from tubeasylum forum, this is all about Japanese Matsushita 12AT7WA Military Grade with gold pins:
Matsushita 12at7WA GOLD...the round logo & seamed top is a dead giveaway. Military contract, I’d bet, based on the gold pins & 3 micas. The top is domed and has gold pins. Is this a high-end japan design.
Interesting tube!
I believe they call that a "pinched waist", and it was done to promote mechanical stability
of the internals for low microphonics. I’ve never seen a Japan tube like that, but I know that
Amperex made some PQ preamp tubes with pinched waists that go for serious $$$.
Really a nice looking tube, though! Quad mica, copper posts, and the getter is attached
at two points vs. the normal one. I’d bet that you could knock on that tube with a pencil
and not hear a thing.
I’ve noticed that tubes from 1958 and earlier have a bigger pinch then tubes from around 1960. Personally. I haven’t seen tubes after 1960 with a pinched waist.
The most well known pinched waist tubes are from Philips Heerlen and Valvo Hamburg. They were made mid to end 50s and have the glass pinched around the top mica spacer. I assume this was done to fight microphony.
They were only produced for a few years AFAIK and the technique was later abandoned by tube manufacturers.
I had always thought the pinching was to clamp the micas in tighter to reduce mechanical vibration of the structure and therefore microphonics.If so, what makes the pinched waist worth making?
Pinched waist tubes have an indented ring around the middle portion of the glass tube. They’re quite rare, and thus quite expensive. I have a single from Holland I need to pair up.
They made a positively HUGE difference in a preamps!