Elrog 300B vs Takatsuki 300B tubes

It seems that there might be an issue with reliability and the 300b....I brought it up as I would love to get the Elrog but not if they fail. Years ago I had the KR-XLS tubes in a Cary 300SEI LX...went thru 3 pair in 18months before Cary stopped using them and stopped the LX.

Hi,I am an engineer at Elrog.

some thoughts about the realiability of 300B (and special ELROG ER300B)...in my bad english.

Yes, we have trouble in a handful of amplifiers when using our tubes...these are some models of "VAVAC", "Border Control", "Nagra" and now the "Franks" (aka. "Frankenstein").
Why?
Ok, let us study the "Frankenstein"...
There we have:
- 525V operating voltage with some drop (25V) over the OPT
- Makes 500V at the Anode
- because the 1kOhms cathode resistor we have 86.8V at the cathode
- results about 413V anode voltage
- at anode current of asbout 87mA
- so we have a plate dissipation of 35.93 W

35.95W this is very,very close to the WE datashhet for the maximum plate dissipation (36W)!
The old datasheet of the 300B says 400V Anode voltage as MAXIMUM...413V? In the newer version some "Recommended Operating Condititions" are included...the MAXIMUM anode currrent is specified at 80mA...not more...87mA?
Ok, the ABSOLUTE maximum is specified at 100mA...using self-biasing circuits...

And readable also:
"The life of the tube at maximum operating conditions will be shorter than at the recommended conditions"...how much shorter?...8000 hours 9000 hours...?!?

And now we return to the first point..."Design Center Values" of a tube...
Since all the times, tubes have a deviation in parameters...if not different specified, 10% are absolutely normal.

So, if I am a good ingeneer I go a little bit below the maximum ratings (this 10%)...And then I think about the deviations of the "mains"...115V are correct...but, what if there are 120V (or 110V)...there are another 5%...

Thats why I think the "Frankenstein" is NOT well done.
All is "on the edge".
It is very simple... a cathode resistor of 1.2kOhms will do the job...
The decrease of power is very small and the decrease of distortion is small also...BUT the tubes will last much more longer...doesn't matter this will be WE300B, EML300B TAK 300B ore ER300B ;-)

Regards, Matthias

Matthias,
Thanks for your contribution. Goerge Lenz of tubesusa.com called me today and gave me this explanation.I'm somewhat confused as Coincident president Israel Blume says the Frankenstein has a conservative design and is easy on the 300b tube. I'm no engineer and I accept what he said.My EML XLS seem to be doing fine with tthis amp(so far,2.5 years).
But again that's a different tube design.If a simple resistor change solves the problem that's good news(assuming there are no adverse effects of doing so).

George mentioned that there are plans to "tweak/modify" yhe Elrog to improve compatibility with certain amplifiers such as Coincident. Matthias the Elrog ER 300b sounds simply terrific in this amplifier, so congratulations! I sure hope the issue can be successfully resolved. The discrepancy between you and Israel Blume puzzles me(it's either tough or easy on the 300b).
Best Regards,
Charles,

Charles, it sounds like you may have to do this resistor change to make the 300B last longer. If they do tweak this tube you may want to wait for that replacement. If you just get another one from this batch I probably would do the resistor change. It can always be taken out in the future.

Jeff,
George is only going to use the modified tubes from this point going forward, so these will be my replacement Elrogs(when they're ready). The resistor swap option seems simple once I know which one to change(you think Doug could help?). I'm very encouraged and hopeful.
Charles,