A friend on this forum picked up a beard ca506...... to cut a long story very short this unit has a pair of mystery valve ie valves that have been rubbed to remove the id of the valves ...as all the other valves were original beard labeled I think we can assume the mystery pair are like wise original..... After contacting the chap who has taken on the servicing of these units ...to be told "there special and you can only get them through me"....Which at once raised my suspicions... a quick trip to hotroxuk id them as possibly a rather poor pair of chinese ecc81 ! So this is a salutary lesson ....... don't always believe every thing your told.
