Thomas, is there a preferred operating point for the Elrog 300b tubes? For example an operating point of 350v across the plate @ 60mA would be considered a traditional operating point for the 300b. Some amps run the 300b at a much higher point for example 400v or even 450v across the plate @80 or 90mA. Thank you.
Elrog 300b's for sale. Your thoughts?
I noticed this morning an add for the new Elrogs. I and many others on the forum ran the experiment when the Elrogs were initially launched. We found the tubes to be superb sonically, but woefully unreliable. In fact, the early failure rate on those tubes was apparently 100%. I and others received replacements that were hand selected for suitability in our particular amps. In fact one individual had 3 pairs fail. In my case, I went so far as to purchase a PS audio power plant, having been assured that limiting incoming voltage to 115V would ensure reasonable lifetime for the Elrogs. Two days ago, one of my replacements failed, after having been nursed along carefully. Honestly, I doubt the tubes had 600 hours on them. So the Psvane T1s went back in and I began the period of mourning for my deceased Elrogs. This morning I awake to the siren song of an ad from a reputable dealer who is announcing availability of the new improved Elrogs with a 1 year warranty. My initial reaction was, "I don't think so. Someone else can run the $1200 experiment. Burned once and lesson learned." But here is the problem. If all of Elrogs former customers take that approach, the new Elrog will also fail even if the tubes are good for 10000 hours, simply because no one will buy them. The tubes are so good that it would be a tragedy if that happened. So the question to all of you who have already been down this road is this? What would it take for you to give these tubes a try again?
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Thomas, Thanks so much for your response. This dialogue with the company is what I hoped would happen when I opened the thread. I am encouraged by your candor, attitude, and also by the information you have provided on the changes to the tubes and resulting gains in reliability. As I have said, the Elrog 300b is a tube of stunning beauty. I want Elrog to succeed and have the opportunity to add additional tubes to its catalogue as time goes on. I would encourage you to drop by this thread on occasion to provide updates on tube reliability. I also own Coincident Frankenstein amps. As you know from my post, when I received my replacement tubes I bought a PS audio P10 so that I could limit the voltage. In addition, the P10 provides for a soft start up where the initial inrush is limited to 1/2 current for the first 5 seconds. I almost never listen for more than about 2.5 -3 hrs, so I had hoped to make the tubes work. I had intended to go with the EML xls as a replacement, and may still go that route. But I am going to put this decision off for a few months to see what transpires with your recent production tubes in the Coincident amps. Can you share with us the number of customers currently running your new tubes in their Frankensteins? I am personally willing to consider the Elrogs again based on your comments, but I would like some statistically significant data on the tube lifetime in the Franks. I don't expect 0% failure, of course. |
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 |
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