AW43-88 short?

[60 oldjohn]

This AW43-88 has two circuits, the heater and the two grids, Just marked g in the Mullard 1970 book. Should the two g be connected internaly?
John.

[Peter.N.]

Sounds feasable if they are both marked the same, the A1 and focus anode connection would be seperate.

Peter

[60 oldjohn]

Thank you peter, I think your right. I have just noticed a2+a4 in small letters near g. The tube may be ok.
John.

[Heatercathodeshort]

Hello John,
I have never known a Mullard AW43-88 to fail. They give 100% brilliant pictures 50 years on. The same cannot be said for the Mazda near equivalent the CME1703..I hope yours proves to be OK. John.

[60 oldjohn]

Thank you John, I hope you are right. At present I have EHT 1/4 inch + spark. But the screen looks the same as when it is switched off. There is slight rustling in speaker. When I get a blank raster I will have to organise a signal.
I have just noticed that one of the g pins is not used, so it looks like they are one and the same.

John.

[audiomagpie]

If, however your tube is at fault, I have a good spare (it's a Brimar C17AA, direct equivalent for AW43-88) that you would be more than welcome to.

Greg

[60 oldjohn]

Hi Greg, Thank you for the offer, I will let you know.
John.

[Peter.N.]

1/4" spark doesn't sound enough to me, try shorting the grid and cathode together, that should give maximum brightness, failing that check the 'A1' pin, you should have several hundred volts on there.

Peter

[60 oldjohn]

Shorting grid and cathode did nothing. No voltage on A1.
There seems to some differences in the circuit for the 100u and my 102u set, especialy plug "P" numbering, and different resistors.
John.

[Peter.N.]

The lack of A1 voltage will probably be the reason, its normally derived from the line output transformer. Check from A1 to earth, if its s/c there will likely be a capacitor to earth that is s/c, if not the resistor feeding it is probably o/c.

Peter

[Heatercathodeshort]

As Peter says the components to check are: R619 120K, R622 100K [both probably OK] and the prime suspect C609 .056uf [.047uf to .1uf will do fine] I suggest you snip the earth end of the focus preset mounted on the tube base. This is directly across the boost rail and used to drop dramatically in value lowering the height and brightness. The AW43-88 does not require a focus potential as such unlike it's short neck sister the AW43-89. Hope you sort it. Regards, John.

[Heatercathodeshort]

Just to clarify. The 100u and 102U are basically the same other than the auto contrast control with the photocell. I have highlighted the components to check. Circuit is from Newnes 1960/61. Good luck. John.

[Peter.N.]

Thanks for that burst of nostalgia John, its all coming back to me now - well some of it

Peter

[60 oldjohn]

The focus preset had been snipped years ago and used since as it was covered in the same woolly muck and dust. I have changed a cap and one resistor I have 200v on a1, but shorting cathode to grid still nothing.
John.

[Heatercathodeshort]

Does the EY86 light up? Have you replaced the boost capacitor? The line coupling cap to pin 2 of the PL81. Have you replaced it? All these and more will need replacing in a 50+ year old receiver. The Lopt's have been known to fail but it's early days. John.

[60 oldjohn]

I assumed the EY86 would be lit being a U chassis I should have read circuit. On cleaning the muck off EY86 just a purple spark and EHT noise which I assumed was at CRT end but is from the valve. The only valve I have is marked EY86/87 It also has a ? marked on top of box asuming valve is Ok would it replace the EY86 ?
I have circuit on Trader sheet 1460. I can see Boost cap on circuit but can not locate it in set.
John.

[60 oldjohn]

I just tried EY86/87 got a raster with 1/2inch gap top and bottom I will check associated resistors. The raster is pulsing about 4 times a second by 1/4 inch any ideas of the culprit? Possibly main smooting can?
The signal I intended using was a Labgear Colour match, I just fished it out from the junk pile to find it is 625 only, I remembered it was VHF UHF.
John.

[Peter.N.]

Does the pulse rate vary with the brightness? If so check under the EHT connector on the tube for corrosion.

Peter

[60 oldjohn]

No change to pulse with brightness. Boost cap 0.047uf on trader, 56,000pf removed from set,, replaced with 0.068uf, is this ok? Pulse was same before boost cap changed.
John.

[Refugee]

Could it be a gap in the aquadag earth?