Murphy V659 LOPT Substitution

[Murphyv310]

Hi.
The copper strip around the jellypot needs to be earthed. just use the existing black lead that is earthed and solder it to the strip near the clamp screw.

You could of course try the stabilised circuit that David Boynes posted up, using a germanium diode solves the issue of not finding the correct VDR.

[Geordie McBoyne]

Peto-Scott continued to employ the stabilised line timebase circuit until the introduction of 110* CRTs in 1959.  The later production models with stabilised LTBs employ a valve instead of the crystal diode.  In the circuit shown in the attachment one of the diodes in a PABC80 is used, some sets used a diode in the EBF89 sound IF amplifier.
So more reserve power is needed if you wish to use a LTB stabilising loop and the jelly pot can supply plenty of of that. Many, many years ago a BRC 950 Mk2 came in for repair, evidently the last repairer had given up trying to fix the set. Someone had wrote inside the cabinet "died in 1968 of too much EHT". Of course the fault was in the stabilising circuit and it was a simple matter of replacing all the components in the LTB, the VDR width control and the feedback capacitor.

Geordie McBoyne.

[Geordie McBoyne]

The ways things are going with my Murphy V659X another line output transformer will have to be found and fitted. 
The set works OK for an hour or so but if left on longer than an hour the left side of the picture becomes compressed and the oil filled transformer can becomes very hot, in fact too hot to touch.
The set has an ultrasonic remote control system. The channel change has never given any problems but the sound muting has never worked, this week I decided to sort out the sound control in the remote control receiver.

For starters the mute button on the remote control handset had jammed. Dismantle and reassemble the handset. but that doesn't solve the mute function fault. The remote control receiver is tuned to 43.6Kc/s for channel change and 46.6Kc/s for the muting. The channel change system has never given any problems but there's never been any activity in the sound control channel. The tuning coil coil was found to have green spot corrosion on the tags of the coil assembly. That fixed a pulse of 20volts is available at the grid of the relay driver valve V23A (6/30L2)
But still the mute function doesn't work. The relay wasn't responding to to signal from the remote control although the pulse signal is present at the anode of the valve. Just a sticky relay which responded to little adjustment. Finally, the sound muting switching contacts needed attention, that done the sound can now be controlled from the remote control handset. On the Murphy the level of the sound can be adjusted by a pre-set control situated at the back of the receiver.
Fully muted or the sound level of choice.
As you would expect from Murphy the remote control handset is a beautiful piece of over-engineering.

Geordie McBoyne.

[Spot Wobble]

Thank you for your post plus video and photographs Trevor: I'm full of admiration for your work.

One thing that I am curious about - minor point, I know - is the tuner selector switch on this set: is it a rotary dial or push-button selector? I notice that there is a pointer marked in its centre.

Best wishes,

Francis

[Murphyv310]

Hi.
It has a rotary cam. Press one button and the turret goes to that selection, same with them all. The pointer is connected to the turret shaft

[Spot Wobble]

Thanks Trevor.

Interestingly, I notice that there appear to be two buttons saying 'BBC' (as opposed to 'BBC 1' and 'BBC 2') - ditto two 'ITA' buttons - so I am guessing: if the set is 625-line capable, it was perhaps built a little before the start of BBC 2 in 1964, and perhaps another ITV (ITA) channel was a possibility at the time too?

Best wishes,

Francis

[Murphyv310]

It is 625 line convertible but the tuner for 625 is separate. The VHF tuner though as the extra positions for use with say a close by different region and programming.

[Spot Wobble]

The Bush 'Nineteen' set that I have has two 'BBC' buttons and two 'ITA' buttons, all without channel numbers to them.

At the bottom is has '405' and '625' selector buttons, but the mechanical linkages to the buttons are not connected to anything, and the set never had a UHF tuner fitted to it (although I understand it had a space reserved for that tuner behind the Bush badge near the top of the loudspeaker grille).

I have inserted 625 video into the set (via a system 'A' VHF modulator) and you can just get a 625 picture to lock at the extreme end of the horizontal frequency adjustment.

Regards,

Francis

[Murphyv310]

Some sets will lock if the control has sufficient range to 625.
Youll get lack of width and the current through the LOPT will increase. People did this on the British Relay line to get BBC2, then they wondered why they needed a new LOPT, line output valve and efficiency Diode.