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Old 22nd May 2020, 6:31 pm   #1
BrianAllen
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Default Bush PB.12 Stray Wire

Try as I may, I just don't have the experience of wiring diagrams, to identify the orange wire from the soldered lug on the transformer leg/support (there is a black wire on the lug which comes from a tag on the transformer).

Does anyone have any idea where this orange wire should be attached?

Thank you.

P.S. I am still searching for a CL 33 valve; have tried all of the usual places but still no luck!!
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Old 22nd May 2020, 6:45 pm   #2
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Default Re: Bush PB.12 Stray Wire

As shown in the chassis view in the service sheet, that's the voltage selector.
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Old 22nd May 2020, 6:59 pm   #3
BrianAllen
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Default Re: Bush PB.12 Stray Wire

Hiya, not the one on top with the green plug; the long orange wire below (it has a lug on it that obviously needs to be bolted/attached to somewhere, not obvious to me.

Thank you.
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Old 22nd May 2020, 7:08 pm   #4
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Default Re: Bush PB.12 Stray Wire

Bush often use screw terminals on the speaker transformer connections.


Where does the attached connection go.


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Old 22nd May 2020, 7:17 pm   #5
BrianAllen
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Default Re: Bush PB.12 Stray Wire

This set was part dismantled when it was acquired; hence my query.

There are 2 terminals bolted to the speaker transformer ( one goes to anode on valve 4 and the other to a H.T. line).

All I know is that the orange wire is soldered to that lug which is bolted between the main transformer and the transformer support leg.

Brian
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Old 22nd May 2020, 7:36 pm   #6
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Default Re: Bush PB.12 Stray Wire

Just a thought; as the orange wire is soldered to a lug that is bolted to the transformer support leg, could it (the orange wire) be a common/earth connection that needs to be bolted somewhere?

Should the speaker/speaker transformer have a common/earth connection?
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Old 23rd May 2020, 9:42 am   #7
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Default Re: Bush PB.12 Stray Wire

Re: CL33 - there's nearly a full set of valves for this set on eBay at the moment: https://www.ebay.co.uk/itm/Vintage-R...sAAOSwXederDvs except for the CV1581 which is an ECH35 as opposed to the required CCH35. Sounds as if they might be "pulls" but you might be lucky!
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Old 23rd May 2020, 9:53 am   #8
BrianAllen
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Default Re: Bush PB.12 Stray Wire

I have now obtained a CL 33 but will keep an eye that set of valves.

Thank you for taking the time to post the link.

Brian
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Old 23rd May 2020, 6:56 pm   #9
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Lightbulb Re: Bush PB.12 Stray Wire

Hi Brian

My suspicion is that the transformer in this set has a electrostatic shield (or screen), and this orange wire should be connected to that.

I'm not 100% sure, but I think an electrostatic shield is a broad, flat, thin piece of copper (effectively tape) which wraps around the primary coil of a transformer to prevent mains-borne interference being transferred to the secondaries. The circuit diagram in the Bush service sheet for the PB12 seems to indicate that an electrostatic shield is present and connected to the radio chassis.

I think I've heard of internal shorts developing to the electrostatic shields in transformers, so there's a chance that the shield in your set was deliberately disconnected. Of course, somebody could've just broken the lug off the transformer accidentally. You could try and reconnect it (after first checking that the shield isn't shorted to any other transformer connections) but I think the set should work OK without it.
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Old 23rd May 2020, 7:10 pm   #10
BrianAllen
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Default Re: Bush PB.12 Stray Wire

Good evening and thank you for your post.

You have just given me an idea; I wonder if it is anything to do with this plate which as you can see from the attached pic is bolted to the component tag board??

Brian
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Old 23rd May 2020, 7:30 pm   #11
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Default Re: Bush PB.12 Stray Wire

The orange wire is the exact length required (when passed through the chassis) to meet up with the plates first fixing stud/nut.

On closer inspection (with a good magnifying glass) I can see very small traces of blue/green on the orange wire lug; would you agree that this is probably from the plate...…..the plate is only silver because I have cleaned and sprayed it.
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Old 23rd May 2020, 8:43 pm   #12
Wellington
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Default Re: Bush PB.12 Stray Wire

Quote:
Originally Posted by BrianAllen View Post
You have just given me an idea; I wonder if it is anything to do with this plate which as you can see from the attached pic is bolted to the component tag board??
Quote:
Originally Posted by BrianAllen View Post
The orange wire is the exact length required (when passed through the chassis) to meet up with the plates first fixing stud/nut.
Well, it always possible that it could be something to do with that plate, Brian. I would've thought, though, that there was a closer point at which the plate could be connected to chassis (rather than taking a wire all the way out to the main transformer mounting).

Quote:
Originally Posted by BrianAllen View Post
On closer inspection (with a good magnifying glass) I can see very small traces of blue/green on the orange wire lug; would you agree that this is probably from the plate.....the plate is only silver because I have cleaned and sprayed it.
I thought that plate looked rather shiny and new! Was it blue/green originally? I am skeptical, personally - but as you have the set in front of you, you're the one in the best position to judge! I don't think it would do any harm to use the orange wire to connect the plate to chassis.

Are you using a service sheet whilst working on this set? The Bush one has photos of the chassis that may be helpful to you. Curiously, that plate doesn't appear, and I wonder if it was a later addition.
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Old 23rd May 2020, 9:05 pm   #13
BrianAllen
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Default Re: Bush PB.12 Stray Wire

Not exactly blue/green but one of the only parts with no signs of rust on it.

Yes, I have the service sheet but no sign of the plate in the under chassis view.

It may have been a later addition as they did change the location and mounting position of the transformer on later models.
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