Home Tubes Asylum

Questions about tubes and gear that glows. FAQ

Re: Anyone else having problems with NOS 805's?

Mark -

I have limited experience with 805's, but have more experience with 211's and 826's. Most thoriated tungsten tubes have very brittle filaments, and many have been knocked around enough to break filaments. This is usually obvious on close inspection in 211's and 805's. Also NOS tubes are often 40-50 years old, and will become a bit gassy. Heat the filaments for a few hours and many will recover. This may be the cause of the noise you're getting.

You can test 805's btw, at least in a simple fashion. You'll need 2 power supplies and a filament transformer. Just hook up a supply between plate and filament, and a second negative supply between grid and filament. Meter the plate current and grid voltage (negative). Adjust the grid around -100v, and crank up the plate voltage. There should be little current flow at this bias. Then slowly make the grid less negative and watch the plate current. You can draw out curves or just test a single known point with this jig. Gas will often be obvious as a dense blue haze around internal structures or an inability of the grid to stop plate current. I use a 600v adjustable bench supply for my testing, if tubes work fine at 600v they are usually fine at higher voltages.

The most beautiful 805 type I've ever seen is the WE 331A. I have no idea of how it would sound, but it is one of the most gorgeous tubes I own!



This post is made possible by the generous support of people like you and our sponsors:
  Analog Engineering Associates  


Follow Ups Full Thread
Follow Ups


You can not post to an archived thread.