Tube DIY Asylum

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RE: damn Al, then you will need these.

Posted by dave slagle on May 30, 2009 at 17:06:41:
Like the 316, if you run them hard they lose emission quickly. About 4 days ago I started listening to some mesh 2A3's and they were tired. Just for kicks I set the B+ to 250 and the bias to -40V and was only getting about 25ma of current and a Gm of 1500. I remembered the 388A experience and up went the filament voltage and at 3.8V I had 60ma and the Gm was up to 3000 (which is what the tubes measured as new). after a day of use I was running 80ma and I dialed the filament voltage down to about 3.5V. another day and it was 3.2V until eventually one of the tube was pulling proper current at 2.5V and out it went and another tired tube went in. Thus far 2 tubes are much closer to normal and a third is a good way there. The 4th one is putting up a good fight and we may justfind out how long the filament will last at 4V :-)

dave