I have started into my recently acquired GK400. I noticed
the 5514's where changed to 811's not even the A variety. One of them turned into a snow globe. I then noticed it still had the 7.5 filament transformer. Has
anyone used 811s successfully? I would obviously have to change the filament
transformer. I am going to put a want add in the proper category for 5514s. Just looking for others experience my Johnson 500 uses 811A"s so. does my GK500.
Johnathan N8QPC
I have seen this before. Obviously the 811 or A version will not last as long because of the higher filament voltage, but the specs for any tube is +/-10%, making the top at about 7 volts, and maybe a bit more. That means the 811s will last longer than you expect.
You can add a resistor to the input side of the filament transformer to lower the voltage if you don't come across the 5514s. Don't be concerned about the difference between the A version and the plain 811. In this application they will be fine.