The PA "Valve" in the TT Paraset

The Valve case that has been "Doctored" so that the inside has been completely removed.

The side has been drilled and countersunk to take a 3mm counter sunk bolt.

The heat sink to fit inside the valve case above and have the IRF 510 secured onto it with insulating washer etc.

The curve of the back of the heat sink matches the curve of the inside of the can. This was achieve by machining in a lathe a piece of brass and then cutting off the necessary slice.

It you do not have such kit then a file will do the job but take much longer!!

There IRF 510 with the insulation to the bolt hole in place. Behind the "tab" of the transistor will go an insulating washer and the the whole assembly will be bolted inside the valve case.

Note the insulated extension wires attached to the "legs" of the transistor.
The diagram shows the component IRF510 identifying the pin out and circuit symbol as used in the "PA" Valve.

This is an extract from the TT Paraset circuit shown elsewhere and the pin out is the valve base

Clockwise numbering from 7 o'clock starting with pin 1 as seen from underneath the holder. The socket it plugs into is called an "International Octal" base (aka IO)

If one looks at an INTERNATIONAL OCTAL SOCKET...the pins are numbered !

BUT

BE WARNED, WARN OTHERS. SOME "OCTAL BASES" ARE MAZDA OCTAL (aka MO)...LOOK THE SAME, PIN SPACING DIFFERENT.....6V6'S ETC WILL NOT PLUG IN THESE BASES. CHECK BASE BEFORE USE.

Not to confuse you but this is the numbering inside the valve case which you will need to know to put the wires from the transistors in the right places.

Here we have the valve base with the white dot for identification between pins 1 and 8 and the long wires on the IRF 510 have been placed in the pins 8, 7 and 6 which is correct just as a try out as you will need to fix the IRF510 with insulating between the tab and the heat sink secured by a counter sink bolt ( which in the picture is the wrong way round the bolt head needs to be on the outside).

The other transistor BFY 51 can be fully fitted, and soldered in, before closing the case ensuring that no part of its case touches the case of the valve.

NOTE: None of the pins of the base must be shorted to the metal case.

NOTE You may be lucky and extract the base from the body without chipping the base - if you are very careful - but should you crack the base reassemble possibly using a "Super Glue" and then strengthen up with Araldite® or other two part epoxy resin.

Here is a damaged valve base repaired with two part epoxy resin so all is not lost.