HAMEG 205-2 repair

[LorenzoDaniele]

Hi,

I just started repair of  HAMEG 205-2 CRO from Ebay ( listed as not working ) and noticed all power devices on the edge of the "XY" board, supposed to be dissipating in the back chassis plate were all "flapping in the breeze" i.e. no more screws washers ecc. . Looking at some photos and videos I saw how those parts are fixed. Particularly  I'd like to ask if somebody knows what are those very thick white insulators (with plastic screws ) that fix the final Y amplifier transistors BF458 and if they are easy to get or to replace. I suppose the original design did not choose ordinary mica or conductive silicone foil due to their very low thickness and resulting  parasitic capacitance from collector ( back of the TO126 package ) to ground  that would be very bad in this point  ( i.e. shunting the deflection plates to ground ). In fact those white spacers look almost 1 cm. thick , but they must be also a good thermal conductor !!??  I also decided to replace the BF458s  ( T2105-T2106 ) but they are marked as "selected" on the schematics. I am not sure if to do matching selection on Vbe or on Beta. Any ideas ?   Thanks !