The backstory: I've been kicking around the idea of building some more microphones-- namely a "U47-inspired" mic. The U47 used a tube called a VF14 which is nearly impossible to get. They only ever made about 25,000 and most aren't good enough for mic use-- but to even "roll the dice" will cost you about $2,000... then you may or may not have a usable tube. Ouch!
This led to researching alternative tubes, and then tubes in general, from the audio engineering side of things.
Turns out there are one or two guys (one guy in particular) with such a passion for audio tubes that he knows literally more than anyone I've ever seen on the subject. His name is Oliver Archut and he's very well-respected in those circles, as the man behind TAB Funkenwerk, one of the most respected restorers of vintage microphones.
He has, in my opinion, the definitive answers about the "why do NOS tubes perform better and last longer?"
I always heard that it was foremost a difference in materials grade (I'd always heard 'laboratory grade' in the old tubes versus 'industrial grade' in the new tubes) and general build quality. Turns out that is pretty much right, but it gets deeper.
First of all, according to Archut, Mike Matthews/EH/New Sensor are generally pretty responsive to his criticism and feedback. Their tubes have improved a bit, but most still are not there. However, JJ is very stubborn and will not listen to any criticism of their tubes, and will deny all shortcomings. This is interesting to know.
After some of the new EH/New Sensor EF806 failed his 10,000 hour lifetime test, Archut wrote the following:
And then he goes on, with even more "meat:"After the lifetime test I took all tubes apart and checked what went wrong, and aside that everything was made sloppily and not right looking, compared to a real EF806 as well as measuring, the biggest joke is the filament. The historic Telefunken EF806 had a double helix filament were the Russian samples had just a spiral one, resulting in a higher noise floor.
Even the gold plated first grid cannot make up for the sub-standard of the raw materials..... The designation EF806s is given wrongfully.
As a manufacture of mic pres I use at least 600 EF86/804/806 a year, and I have had hoped that Mike would come up with something that is at least better than the EF86 made in East Germany, but quite frankly this tube is just plain old not useable in a mic, nor mic pre, etc.
Many of these things can and will apply to the tubes we use as well.Over the last 10 years I talked numerous times with Mike, JC and even Irushka in Russi
There are two big factors with Russian tube manufactures why their tubes never can live up to old Western specimens:
the production steps they CAN NOT DO and the production steps they DO NOT WANT TO DO. Aside of that, the raw material' situation is quite poor and even tough I supplied Mike and JC with the companies' names which still make some of the material they needed, nothing happened so far.
The problems in detail:
One of the biggest problem with Russian tubes is the cathode/filament and then 2nd is the chemical procedure that applies the active coating to them.
The noise Klaus talks about is a barium coating that gets deposited onto the first grid after about 200h. This makes those tube too noisy even for simple applications with a 3 Meg Ohm grid leak; using a gold plated first grid won't help that problem- in fact it makes it even worse.
The 2nd problem is the isolation coating of the filament that deposits small traces of magnesium onto the entire tube electrodes.
When disassembling a used tube you can see those problems for yourself just by holding the grid(s) into a flame and seeing how the color turns greenish. A new tube that you take apart and subject to the same test won't show those colors)
I am still hoping that the remaining tube factories will notch up the quality so that those new tubes are useable in studio gear... But I do not see that it has happened so far.