Murphy Barrel sets

[Murphyv310]

Hi.
At the moment I have three Murphy barrels sets. A V320A. V330 & a V410, I did have a V530 but this is in Bob's Museum in Sorn.
All three need a but of titivating up a bit, here is some screen shots today.
   
V330.

   
V320A

   
V410

The V410 picture is a little out of focus which is my 12 year old camera having a hissy fit. All three sets work but the V410 has LOPTX issues when hot, the V320A has intermittent hum and the V330 CRT is actually low.

[peter scott]

Hi Trevor,

I think I have a picture of your 330 taken 9 years ago.

Peter

   

[Murphyv310]

Hi Peter.
That was the V310. I gave it to Mike Calvert in Cramlington a few years ago for a swap with an Ekco T368. The V330 came from Chris Whiting.

[Murphyv310]

Hi.
Well the V410 doesn't have LOPT issues. The lack of width, decaying EHT and poor focus was down to low line drive and distorted drive waveform. The line oscillator on all these barrel sets use 10% tolerance resistors, no doubt for good reason. In the V410 all the resistors were way out of the 10% tolerance with two high value ones 30% high. Replacing all of the resistors gave me an increase of 20v p-p drive and a correctly shaped waveform as in the manual. The capacitors had previously been replaced as had the 30P4 screen feed resistors. A three hour run over the weekend and about four today showed up no line problems, the LOPT runs noticeably cooler.
The set does need realignment as the phantom twiddle has broken all the cores, sound and vision are not correct, sound is good and vision is well off and vice versa, there is also bad ringing on vision too.
Any good ideas how to extract chewed up hex dust cores?

[Terry]

Any good ideas how to extract chewed up hex dust cores?

It's a long time since I've done it, Trevor, but the only way is to break them up completely and pour the bits out. If the twiddler hasn't got at both ends, remove the lower core to provide an escape route for the bits.

With care, you should be able to drill through the core with successively larger bits. This removes a lot of the debris and makes it easier to break up the (thinner) remains.

Good luck!

[Murphyv310]

Many thanks Terry. Yes as far as I can see the least accessible side is ok.
This screen shot shows up the ringing on the 3Mhz bars, you can see ringing on the verticals on the test card, results on band 1 are poor, this picture is from channel 9.
Sorry about the picture as it's just one field, 188 visible lines, bloomin digital cameras!!!
   

[Geordie McBoyne]

I recently worked on a V410.   In my opinion this the best of all the Murphy barrel sets.  After doing a recap job the frame linearity was still bad. This turned out to be a hidden capacitor. C92 is positioned on the centre panel which has the main voltage selector. Also, as a matter of course replace the screen grid decoupling capacitors of the sound and vision IF amplifiers.   These 0-001microfarad capacitors are of the type that resemble resistors in as much they have coloured bands. I believe this type of  capacitor was used because it has a degree of inductance in order to give a reaction effect to in increase the gain of the amplifiers.  Of course I could be wrong.   Nevertheless, the receiver has exceptional gain characteristics.  It displays a healthy snowstorm on the screen on no signal conditions.  something you rarely see on a TV receiver that has only one common vision and sound IF amplifier and single IF stages for vision and sound.
The attachment shows the position of C92 which is in the frame linearity feedback network.

Geordie McBoyne.

[Murphyv310]

The mains carousel panel swings out after removing six PK screws and the two dropper self tappers.
Normally I wouldn't expect to see a snow storm on a V410, just a little noise on screen. Make sure that all decouplers are ok, AGC action may be holding off a little instability, you'll see if that's the issue with a weak signal.

[Geordie McBoyne]

Circuit diagram of the vision stages of the Murphy V410A.
Note the position of the V4 screen grid decoupling capacitor C19. Instead of going direct to chassis the capacitor is returned to the "top" of the IF transformer primary so in essence forms a capacitive bridge circuit.  I kinda remember there was a similar circuit arrangement in an earlier Murphy TV, was it one of the V200 series?

Geordie McBoyne.

[Murphyv310]

Hi David.
This circuit is also used on the V510/530 and I think the Astra as well. On the V510 & V530 the upper decoupler (C46 on the V530) was changed to 1800pf and is an official mod for the 410 through to the V530. The mod is in the V530 service manual and was in Murphy News sometime in 1960.

Today I managed to drill out two damaged cores and free off the rest that were OK. I did a quick spot alignment with reasonably good success. Tomorrow I'll do a full realignment with a Digital signal generator for 100% accuracy.