Differences Between A640, Z146 & A793 Line Output Transformers

A640 (405/625 chassis)

LOPT A643 (RBM) or A682 (Plessey)

LOPT core connected to chassis (via tags 3 and 13)

LT supply derived from a separate winding around LOPT core (tag 1)

LOPT desaturation choke 3L4 fitted, with ac coupling components 3C20 and 3R76

P/S6-3 goes to system switch 3S2c (625 contact) on the timebase panel

3R27 (EHT rectifier heater ballast) is 0.48Ω

One end of secondary to primary (on 625 only) coupling winding (tags 12 and 13) is connected to chassis (tag 13 to tag 3)

3R77 (line pulse feed to Boost HT stabilisation circuit) is 68k Ω

3C25 (420pF) and 3R79 (200Ω) connected in series between P/S6-1 and P/S6-4, on timebase panel

Z146 (405/625 chassis)

LOPT Z189 or Z190 (electrically similar to A643 and A682, respectively)

LOPT core NOT connected to chassis

LT supply NOT derived from a separate winding on LOPT core, but from an additional tap on secondary winding (tag 3)

LOPT desaturation choke 3L4 fitted, with ac coupling components 3C20 and 3R76

P/S6-3 goes to a system switch 3S2c (625 contact) on the timebase panel

3R27 (EHT rectifier heater ballast) is 0.6Ω

One end of secondary to primary (on 625 only) coupling winding (tags 1 and 6) is not connected to chassis, but to tag 1

3R77 (line pulse feed to Boost HT stabilisation circuit) is 27kΩ

3C25 (420pF) and 3R79 (200Ω) connected in series between P/S6-1 and P/S6-4, on timebase panel

A793 (625 only chassis)

LOPT Z157 (RBM) or A792 (Plessey)

LOPT core connected to chassis (via tag 3)

LT supply derived from a separate winding around LOPT core (tag 1)

LOPT desaturation choke 3L4 AND ac coupling components 3C20 and 3R76 are NOT fitted

P/S6-3 function changed. 3R79 (200Ω) is now fitted on LOPT (between tags 2 and 5) and tag 5 goes to P/S6-3 and thence to 3C25 (420pF) on timebase panel. The other end of 3C25 goes to P/S6-4

3R27 (EHT rectifier heater ballast) is 0.48Ω

The secondary to primary (on 625 only) coupling winding (tags 13 and 14) is connected as follows: tag 13 to tag 4; tag 14 to tag 2. Neither is connected to chassis.

3R77 (line pulse feed to Boost HT stabilisation circuit) is 68k Ω