I recently acquired a British KW1000 linear which uses a pair of 572Bs and is somewhat similar to the SB200. The power transformer was missing but I have been able to fit a replacement from the junk box, it has 2 x 6.3 volt 4 Amp winding with no centre tap so am thinking of connecting the filaments in series. The first problem with this is one tube light up brighter and had 7 volts, the other 5 volts (these were old tubes, one Centron, the other Taylor). When I tried a newer matched pair from Penta the voltages were quite close.
Looking at the schematic for my TL922A I see the CT is connected to the linked filament pins via a 80 uH choke where the drive appears to be applied, although there is also a 0.01 uf capacitor whose purpose is unclear to me, across to one side of the main choke (22 uH).
Any advice would be appreciated, also is any bias required in tx and is there a need for neutralization? - am directly grounding the grids. The KW1000 has a few additional turns on the filament choke which goes to a flat plate about 1" square and close to one of the tubes.
Mike
VK2AMF / G3XEF.
Mike Fleetwood
Canberra Australia and Sidcup UK.
Worldwide email address is: mfleetwood@...
