Bringing an Ameritron AL-811HXCE back to life - part 4

So....

Rewound / rebuilt the choke (see part 3), and so now onto the parasitic board. Now this was very badly burned up, carbon in many places as you can see from the pictures (apologies about the quality of these!). The odd bits of wire coming out of either side are actually the HV feed to the 811a anodes cap and yes you've guessed it, they are badly over heated / damaged.

So now I've got to make another one. 



As you can see from the third photo (what is meant to be the copper side) it was in a very bad way

Anyway, I thought I could see where copper should be and that together with the circuit diagram and some interpolation gave me a bit of a head start.


So I removed all of the components from the PCB and then carefully looked at what was left. The short answer was not much !!!

But it still had holes, so first step was to get some paper, place the board on it and then use a thin instrument (I used a long drawing pin!) to punch through holes to give me a location of where the component leads should go. From there I looked at the damaged board very carefully and slowly reconstructed where the copper should have been originally.

I then used this to transfer the tracks it onto a Copper (Single Sided) PCB substrate, using a combination of rub on transfers and PCB etch resist pen. I then etched this in the normal way for making PCB's using etching fluid, there plenty of web pages that show how to do this so I wont bother.

Anyway the result is shown in the fourth photograph  with the other (original board) shown below - just a little different !!! . This shows the copper side, and the odd black squares you might able to vaguely see are on the non copper side and mark where the components for the board should go so I don't forget.

I then drilled the board with suitable holes (the coils and resistors need a larger hole than the capacitors. 

I then looked at the components I had taken from the amp, I carefully measured them and (somewhat unbelievably) they all measured OK !! - Anyway the PCB cost me nothing and goodness knows how many heat cycles they had been through, and they were bound to fail sooner rather than later so I decided to get new components and of course wind new coils.  The components have been ordered and should be with me in a few days. I've already wound the coils and found some decent braid to use for the four connections to the anodes, so the assembly should be a nice straightforward job when they arrive.


I've also order two lovely doorknob capacitors from the Ukraine (again courtesy of eBay) which are 2.2nf (2200pf) 10Kv. One of these I will use to improve the blocking capacitor as per the article from DC9ZP. The original one is 3 - 4Kv I think. They look great on the web, I await their arrival with interest.

On the subject of High Voltage components, has anyone noticed how many items (especially above 5Kv) seem to come from the ex soviet union / Baltic states - wonderful quality and (I think) great prices - even after paying import duty. Its definitely worth considering them if you need such things in my opinion.

Until next time 73's