This Valve is marked 6BQ5 Philips GT-Britain KM1 83F4 ? Some of the writing is faded.

It was wrapped in brown paper and in a box which does not correspond to it but I will send it as it was found.  I have no way of testing but all the other valves I have found and sold, so far, have been working fine (via buyer feedback) - but the brown paper it was wrapped in did have the word OK on it and I suspect he would not have kept it if it was not working.