Murphy V204

[Radio Tech]

This is certainly a blast from the past, I acquired this vintage set from a farmer way out in the sticks, the set had been stored in a huge barn and was last used to watch the coronation in 1953, the set its self nearly landed up on a bonfire heap and just by chance it was rescued by a brother of mine who was doing some work for the farmer. The cabinet has taken a bit of a turn for the worse and it seems the loudspeaker has been taken but what a huge tube this set has got, a 15 inch round and a long neck supplied by a company called Day Lampex who were based in Southend so does this mean that Murphy Radio had the set built by Ekco? Its going to take a lot of TLC to bring it back to life though, most of the valves are there except for two and the circuit I have does not show the valve layout so maybe someone can help. The set has got a band converter which was fixed to the top of the set outside again made by Murphy.

Best wishes, more to follow

Ken

[Radio Tech]

Her are some photographs of the chassis for this television set, as you can see it is very dusty and dirty which has gathered over the years since 1950. I will of course have to replace the waxy caps and the electrolytic capacitors, quite a task and there is the cabinet to sort out but I will have to be very careful getting the tube out of there. I haven't yet found the output transformer for the sound.

Best wishes

Ken

[FERNSEH]

First picture: that transformer fitted to the CRT support bracket is a booster or isolation transformer for an ailing tube, most likely it was employed to force a little more emission from the original Mazda tube. Day Lampex? An independent CRT rebuilder.
The set looks a good restoration proposition.

DFWB.

[Heatercathodeshort]

Hello Ken,
I would take that 'not used since 1953' with a pinch of salt. The model was released in 1952 and was fitted with a band 3 tuner in 1955. Add to this the rebuilt tube and by the look of it was probably used every night until 'The Queen.'

I have the slightly later V214 awaiting on the production line with it's original tube. It reads ok on 'Bertha' so there is some hope. The CRM152B/153 were another disaster for Mazda but when they are good there is no comparison.

The model was produced at Murphy Radio, Welwyn Garden City. They had production hold ups due to Mazda not being able to supply all the 15" tubes that were required.

I doubt if that rebuilt tube is any good. Shoot me down in flames if it is but don't waste time rebuilding the chassis until you have checked the tube. Being a triode [if it is the 152B, the 153 is a tetrode with ion trap] it should be simple to get 'First Light, the best test of all. A good replacement is difficult to unearth.
Regards, John.

[Radio Tech]

Thanks John and DFWB, I am just wondering the best method of getting the tube tested, as I don't think I could test this on my home brew valve test, could it be done on a mullard high speed valve tester? I am going to start repairing the wooden case first which will take a fair while to do, got to treat it for wood worm and then do the veneer which is bad.
John have you got the component layout, the chassis top and bottom so I can identify the components a bit more easy.

regards

Ken

[Horris]

Hi Ken
The CRT is a rebuild by a company called DayImpex. The didsome very good regun tubes.
They are still in existance but not producing CRT's . The are based in Earls Colne Essex.

Dave

[Peter.N.]

Nice clean chassis considering where it was found, especially the underneath, obviously been kept dry. I wish you well with the refurb.

Peter

[Radio Tech]

Thanks Horris for info on Day Impex, I will most likely look the company up as they are not far from me. And Peter, thanks for the comments on the chassis, its going to take a long time though to get it better. I have got to find some way of testing the tube, just a matter of getting a B12 socket and a male IO plug, I might be able to then test the tube after I have made a fly lead.

Regards

Ken

[FERNSEH]

Might be the same firm: http://www.day-impex.co.uk/ In fact if you read the company profile it was that firm.

DFWB.

[DAC10 Collector]

Originally Posted by Radio Tech

I haven't yet found the output transformer for the sound.

The output transformer may have been directly mounted on the loudspeaker.

This will certainly be an interesting restoration, particularly as the chassis is in good original condition.

Mike

[Heatercathodeshort]

A very basic test to check if there is any emission is to simply power the heater and check with your AVO for diode action between the grid and cathode. [base removed] You should get a reading with the leads one way and nothing when they are reversed.

Great to learn the tube rebuilders had a reputation for quality. At least you are in with a chance, most were not too good.
The 15" ones seemed to suffer from bad vacuum after rebuilding. They were a huge bulb and difficult to fit in some ovens. John.

[Radio Tech]

Hello Mike, I traced the wiring from the anode of the 6P25 and it lead to a transformer, but still can not make out how the secondary connected to the LS, yes I agree, it could have had a transformer on the LS but doesn't explain why the transformer underneath is connected to the anode. Thanks for the info on the basic test for the tube John, I am not going to raise my hopes too high though, I am still pressing on though to achieve a working set. This to me is Great British piece of history, something that at least was designed and made here.

Will keep you posted on progress

Regards

Ken

[akuram1]

Never saw a V204 as before my time but Murphy used to connect the loadspeaker via the chassis fixing screws on later models such as V310 V410 etc.

[Radio Tech]

Yes one lead from what I consider to be the o/p transformer is down to deck the secondary and of course one side of the primary down to deck but not worked out yet how the LS was connected all be it the common side. I checked the HT after replacing main smoothing cap and it seems that the HT is not what it should be, and that is 250V but only reads around 160V, I think the metal rectifier is up the creak.

Regards

Ken

[Radio Tech]

Hi everyone,

I powered up the chassis to check some of the HT voltages but the initial rectified HT is not as it should be either side of the smoothing choke, although the main electrolytic has been replaced the HT after valves have warmed sits around at 150V off the rectifier and around 140V the other side of the choke. So far I have replace all of the waxi caps and electrolytic capacitors, the voltage off the mains transformer is 200V AC but I wonder now if there is something else dragging the volts down, 200V times 1.414 should be around 280V. Any idea's

Regards

Ken

[Radio Tech]

Hello everyone,

Just thought I would just let you know how this old set is coming along, well I have replaced all the capacitors, not yet started on resistors but the few I have checked are within range of their tolerance. The main problem at the moment is trying to find out why the HT is down by 70 Volts, I am beginning to think it could be the selenium metal rectifier which is not right, the cabinet I have been working on is now wood worm free and just in need of the right coloured stain and varnish apart from one area where it has lost its veneer at the front down at the bottom where the badge is.

Be a while yet before I can get the chassis to work as it would have though.

Ken

[Radio Tech]

Just a little bit more, I have now got the HT to what it should be, now all I have to do is find out why no line oscillation and no EHT, once I have got that far I can then work on the sound.

Ken

[julie_m]

Merionesian curiosity makes me ask, what was up with the HT? Was it just a poorly rectifier, or was something dragging it down?

[Radio Tech]

Hello Julie

Having the correct voltages on the HT line is important and anything that either drags it down or a component such as the selenium metal rectifier in this case was not allowing the AC component to be rectified properly, these type are dreadful things and are best replaced which I did. The snag is now I have got to try and locate the main source of trouble, working back to front to find the component (s) that are not allowing everything to work as it should. Going to be a long job this. What I could do with is a schematic of the valve layout viewed from the top side of the chassis as this would make it easier to trace back through the stages.

Regards

Ken

[Radio Tech]

Here is a little more on the progress of the V204, had all the valves out of their bases, had to use some wd40 to free them up though, I found a 12K resistor behaving rather strange, when the power was applied I noticed a very brief flash within the resistor itself so have changed this component. Ken