Elrog 300b's for sale. Your thoughts?

All,

thanks a lot for the positive responses and good wishes. As mentioned in my post so far there was a single beta tester who used the tubes in a Frankenstein amp. He had them for almost half a year now. I wanted to have this test first before releasing the tubes for the Frankenstein. Since this release only happened now, there are no additional users of Frank amps yet who have the new Elrog tubes.

@jetrexpo: The choice of operating point depends more on the amp design than on the tube. As long as all max limits are not exceeded any op point which is preferred by the amp designer is ok. 450V/90mA would already be slightly over the limit and thus is not recommended. I personally use fairly traditional op points of about 350V/65-75mA

@brownsfan: The inrush current issue was solely relevant for the filament supplies. When the tube filaments are cold they are basically a short. If the filament supply uses brute force voltage regulation it will push a lot of initial current into them. An external softstart will probably not do much there. We also saw that some current regulated filament supply kits for DIY amps actually start with a current spike and initially put 7V across the filaments before settling to 5V. This is not healthy for any 300B, but it simply killed the early Elrog 300Bs. Also a tube rectified B+ supply doe snot have any affect on slowing the filament inrush current. But as mentioned the tubes are more robust now to be able to withstand some abuse at turn on. Yet a well designed amp with good filament supply and conservative op points will ensure a longer tube life. Not only for Elrog 300Bs but for any brand.

Best regards

Thomas

Thomas, thanks very much for your excellent responses.  And I second the good wishes extended by the others.

Regarding:

450V/90mA would already be slightly over the limit and thus is not recommended.

I would add that neither number is in itself over the limit.   It is the combination of the two that would result in the tube's maximum power dissipation rating being slightly exceeded.

I say that based on the ratings indicated in this datasheet for the original version of the Elrog tube, as well as on the ratings specified in this 1939 datasheet for the original Western Electric tube.  Although this 1950 datasheet does indicate 400 volts as a "maximum rating, design center value" for the Western Electric tube.

Regards,
-- Al  

Hi Al,

yes you are right, each parameter on it's own is within the allowed limits, but the combination of 450V/90mA results in a plate dissipation slightly above the maximum allowed 40W. 450V * 0.09A = 40.5W (40W max)

Best regards

Thomas

vinylsavor - Thomas,

In purely general terms may I ask what one might expect in terms of hours of life for your "new" 845 tubes?  Some online forums suggested the prior manufacturing of those were problematic as well. Txs

Hi!

As mentioned above the 211 and 845 did not have the issues which the 300B had. They suffered from the poor quality control as well. During the time I was distributor for Elrog I got only very few returns of 845 tubes.

Life time cannot be generally estimated since it depends a lot on the operating conditions. During the many problems with the 300B we learned that there are a lot of amps which push tubes too hard. This can shorten the life time. op point, usage pattern (on off cycling) and tube rolling all affect lifetime. Normally you should be able to expect 3000-4000 hrs from a thoriated tungsten power tube. This can drop significantly if the tube is abused. It can also extend well beyond that number if the tubes are handled well. The distribution is a kind of bell curve

We also do not make the 845 long enough under the new company to have significant statistical data. I do not expect any issues with the 845 though.

Like the 300B the 845 and 211 carry a full year warranty now.

Best regards

Thomas