Murphy V200

[Murphyv310]

Hi.
I have a Murphy V200 on the bench. This is the 4th V200 I have attended to since 1969 which was the first one. The set was rather grubby with thick dust and grime. The LOPT is bereft of its foam covering and the smoother is wrong with only one screw holding the clamp.
Since I removed the chassis its been washed and dried and will be sitting on my toasty bench (under it has a 250W tubular heater) with the dehumidifier running to complete the drying process.
Work starts in ernest tomorrow.

[Murphyv310]

Some further pictures

[Murphyv310]

Hi.
Got a couple of hours on the V200 this afternoon. Initially there was no 100ma valve heaters which turned out to be a non soldered heater pin on a 10F1. I didn't have a good PL38 so a 30P4MR was substituted. Prior to powering up I replaced the following coupiling caps. Line drive, video o/p to sync separator, frame o/p coupling, didn't bother with to sound as yet as keeping the volume at minimum keeps any positive volts off the grid of the 10P14.
Gradually brought up the variac and eventually was rewarded with a noisy line whistle, small spark on the U25 but virtually no EHT, the blue glow from the valve was the giveaway the Visconol EHT cap was in distress, disconnecting it confirmed the diagnoses with a very bright low height raster.
Now to do the rest and tidy up some of the previous work

[ppppenguin]

Is 30P4MR the special version of the 30P4 for some Murphy sets that had self oscillating LOP stages?

[Murphyv310]

Hi Jeffery.
Indeed the 30P4MR was manufactured for the early V310 a selected valve from the 30P4 stock with less drift, probably the best of them. A 30P19 or standard 30P4 will work. In fact Murphy modified the V310 to a multivibrator only months after initial production started using a 6/30L2 awkwardly hidden behind the mains input.

[Murphyv310]

Hi.
Further work done today with some caps changed in the frame and line stages. All were the tubular wax variety and a couple of metallised polythene covered types that showed considerable leakage. The 30P4MR although it works looks under stress in the set, I've no PL38s but a KT36 operates much better, I'll need to see if I can get hold of the correct valve.
There is something coming through the RF and very weak video, as yet I've not been near front end.

[Freya]

The PL38 valves are getting very scarce now, imagine it will become much more of a problem for TV22 restorers especially. Just finished a TV12 that had much reduced width caused by the PL38. Swapping with a known good one from another set gives full scan.

[Murphyv310]

Hi Steven.
The problem is the PL38 & KT36 are designed for timebases that require a linear valve more akin to class A.
Later timebases are more like a pulse so the characteristics of later valves a different I suppose heading to Class C.
The answer is to remove the screen from where it is and return it to HT via an 8.2 to 15k resistor and decouple the screen to ground via a 0.1uf cap. Works in the TV22 so I'd imagine this will work with the V200, did the same mod in the HMV 2807 and a 30P19, Incidentally a PL36 will work so long as pin 1 isn't used as an anchor pin.

[Murphyv310]

Saw this one for sale online. Have complained bitterly to the seller, advertised as brand new NOS.

[Freya]

Saw that too, they appear not to care.
In the TV22 a PL81 has also worked nicely with the usual franken base adaptor, couldn't get it to work in the TV12 though.