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The original trouble with this set was field collapse, the
cause being traced to VT16. The original transistor had no
marking however, other than a couple of dots, and is marked on the circuit as type TVT15. None of this means much to me, but I found that the set could be got working again
by fitting a BC147 in this position. The only trouble now is
field judder, mostly at the bottom of the picture. I’ve checked the height and linearity controls, and both are in order.
Could the transistor I fitted be responsible?
VT16 is the field linearity amplifier and TVT15 is a
Thorn classification, which includes types BC149, BC208B,
BC183LB, BC183LC and BC349B. The BC149 is
probably most readily available. We suggest you fit one of
the approved devices then, if the fault persists, check the
field output coupling capacitor C78 (1,000µF) and its connections and if necessary the output transistors
VT19/VT20. If C70 is 0.002µF, change it to 0.01µF.

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