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Old 18th Apr 2018, 3:03 pm   #1
linescan87
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Default Wakey wakey. Bush T76C

Good afternoon,

The other half has gone on her "hen" do so I'm home alone, so a good opportunity to get this set going. I got this set last year at Mikey's bash, thanks lads. Got it out of the cabinet and on the bench at last, looks like we're off to a good start. The rectifier has been replaced in the past by a BY127 and 33R polo mint dropper. Servicing notes in the 58/59 Molloy & Poole red book.

Cheers,
John Joe.
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Old 18th Apr 2018, 3:29 pm   #2
FERNSEH
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Default Re: Wakey wakey. Bush T76C

Looks like you have the non ion trap version of the Mullard AW43-80, the AW43-80Z.
There's a similar tube in the storeroom upstairs, the exception is that mine has the B8H base instead of the B12A. Mullard were fitting the gun from the 110degree tube in the last few replacement tubes.
You've got one of the best 405 line sets there.

DFWB.
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Old 18th Apr 2018, 3:34 pm   #3
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Default Re: Wakey wakey. Bush T76C

Hi Fernseh,

Yes it is the the straight gun 43-80Z, would this have been fitted from new? Thanks for the encouragement.

John Joe.
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Old 18th Apr 2018, 4:28 pm   #4
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Default Re: Wakey wakey. Bush T76C

Hi Joe,
It's a service replacement. I remember that Mullard made a straight gun replacement for the old 70* MW43-69, the MW43-69Z.

DFWB.
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Old 2nd May 2018, 10:21 pm   #5
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Default Re: Wakey wakey. Bush T76C

Changed the usual caps, got a good raster but very weak rf. Swapping the mixer pcf80 for the video output brought up a good test card. The mixer pcf80 is happy working as the video output but refuses to work in the tuner.

The next job is to re-stuff the main smoothing block. The tube is very good but unfortunately it is suffering from a intermittent partial heater short. I read somewhere that the heater sags and that sometimes turning the tube through 180° can effect a temporary cure.

John Joe.
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Old 2nd May 2018, 10:32 pm   #6
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Default Re: Wakey wakey. Bush T76C

good results in a relatively short space of time! Fingers crossed on the tube
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Old 2nd May 2018, 11:05 pm   #7
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Default Re: Wakey wakey. Bush T76C

Thanks Kevin, I have spare tube should all go horribly wrong. Though the tube is so strong that even when the short is present it is still quite watchable.

Cheers, John Joe.
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Old 3rd May 2018, 7:48 am   #8
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Default Re: Wakey wakey. Bush T76C

Very unusual to have a partial heater short on the AW43-80Z. It has the later gun. Just bad luck. J.
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Old 4th May 2018, 1:08 pm   #9
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Default Re: Wakey wakey. Bush T76C

Running the set yesterday the overwind started to show signs of damp ingress. I am drying it out with the dc current trick, it's taking about 1.5 Watts and nicely warm. I shall leave it for the week.

John, do you think there would be much merit in turning the tube, a tap of a screwdriver handle can make the partial short /clear. Do you think it could be heater sag?

Cheers, John Joe.
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Old 4th May 2018, 6:05 pm   #10
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Default Re: Wakey wakey. Bush T76C

I've never had much success but it's well worth a try. It might just do the trick. The heater is shaped like a letter M and becomes shorted at the centre section. A really frustrating fault and it's always a good tube that suffers. John.
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Old 5th May 2018, 5:12 pm   #11
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Default Re: Wakey wakey. Bush T76C

I've got a Bush TV75 with an AW43-80, and with the same annoying problem. I flipped the crt in this and it worked fine for about 3 weeks then the partial short returned. Some light tapping on the tube neck normally clears it for the duration. I'm still looking for a good one!
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Old 6th May 2018, 8:47 pm   #12
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Default Re: Wakey wakey. Bush T76C

I have the same problem with a Ferguson transportable fitted with a Mullard AW47 91 CRT. The sad thing is the CRT has excellent emission evident when the CRT neck is gentally tapped.

I hoped it would serve as a nostalgia item for work but don't think the the power that be would take kindly to having to remove the bowler hat cover in order to tap the CRT base!
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