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Niechcial,Steve · 10th Jun 2021, 7:04 pm

I have made good progress on this set. I have managed to shoe-horn the KB VC1 LOPT into the LOPT enclosure with the Valve EHT rectifier in circuit. With S-bend caps of 0.1 mfd (625) and 0.32 mfd (405- 0.22 + 0.1), I get good width and lin, correct boost and no foldover on either system. Apart from the S-bend caps, the only other mod. I had to make was to short out the width control inductor. I have given up on the extra windings I put on the LOPT for the flywheel sync because they were beginning to break down. In any case it works very well on direct sync- better than the original LOPT did by all accounts.
Another quirk of this design is that Frame Lin. changes much more with boost voltage/height than on a set with the more conventional feedback lin. circuit.
After Dave's comments on the sound noise limiter rectifier I put it across my variable power supply, but get no current through it, so it is in fact o/c.
I wonder why Murphy went in for this strange amalgam of part PCB and part hand wired construction? The hand wired IF bit immediately below the PCB sound panel would surely have been more cost effective to produce as a single IF panel?

10th Jun 2021, 7:04 pm	#64
Niechcial,Steve Hexode Join Date: Jan 2007 Location: Beckenham, London, UK. Posts: 373	Re: Murphy V659/759 restoration I have made good progress on this set. I have managed to shoe-horn the KB VC1 LOPT into the LOPT enclosure with the Valve EHT rectifier in circuit. With S-bend caps of 0.1 mfd (625) and 0.32 mfd (405- 0.22 + 0.1), I get good width and lin, correct boost and no foldover on either system. Apart from the S-bend caps, the only other mod. I had to make was to short out the width control inductor. I have given up on the extra windings I put on the LOPT for the flywheel sync because they were beginning to break down. In any case it works very well on direct sync- better than the original LOPT did by all accounts. Another quirk of this design is that Frame Lin. changes much more with boost voltage/height than on a set with the more conventional feedback lin. circuit. After Dave's comments on the sound noise limiter rectifier I put it across my variable power supply, but get no current through it, so it is in fact o/c. I wonder why Murphy went in for this strange amalgam of part PCB and part hand wired construction? The hand wired IF bit immediately below the PCB sound panel would surely have been more cost effective to produce as a single IF panel?