Thanks for your reply's. I have the documentation you both linked too and I understand how the pin numbering are arranged. (I have googled it!
) But indeed it seems i made that mistake regarding EF40 when i listed the pins.
First of all I seem to have misunderstood the i.c. label, in my mind it became not connected. On EL41 pin 3 called i.c. is connected to pin 7 and since pin 3 is connected it solves that mystery for me.
However, I can't find any information in the documentation on what the i.c. pin are connected to?
Yes it would seem cathode or K a is floating but so is anode and grid 1,2,3 but that's how a tube is. as depending on design these elements are separated by space..see their physical construction.
I think I was unclear, I meant that the cathode pin where only connected to the socket and no connection was made to the cathode socket pin to the rest of the circuit. I do understand that the parts are separated inside the tube by vacuum.
I have already done the rectifier part that uses a 5Y3 and have no problems understanding the principle since it's a simple dual diode so I do know some of the basics at least.
I had assumed that the anode would always be the outer most active layer but it appears that on the EF41 the beam suppressor is a cylinder fence encasing everything else. Given that the pinout matches that of the documentation.
Also I know about the getter and the black surface coating on the glass, however inside the unit there are two EF42. One marked Mullard as the rest of the tubes and one that has been replaced by one marked Philiphs. The older Mullard tube has the blackish top from the getter like the other ones but it also have an even silver coating that I believe might be from the anode. Is that a bad sign?
//A