A puzzle for the weekend; Bush AC11 transformer bare wires

[BrianAllen]

Well spotted David.

With all of the odd wires here and there and with my level of experience, it maybe best to source a replacement transformer.

Obviously not all transformers are the same, so what will I actually be looking for? I have a few transformers here but I am not yet at the stage of knowing/identifying them.

Brian

[ms660]

Originally Posted by DMcMahon

Brian said in Post 11 that the blue wire connects to pin 8.

If the blue wire (via the brown wire) connects to the rectifier pin 1, what is the grey component connected to pin 2 of the rectifier ?

David

The Grey component connected to pin 2 (the anode) will be a surge limiter resistor to limit the maximum current that can flow through the rectifier if hot switched, originally the resistance of the transformer secondary winding would have served that purpose.

Pin 8 of the UY41 is connected to pin 1 of the UL41, the next pin anti-clockwise from pin 8 of the UY41 is pin 7 which is the rectifiers cathode and is connected to the reservoir capacitor, HT filter resistor etc.

Lawrence

[cathoderay57]

Hi Brian, there's a scrapper Bush AC11 for sale on eBay located in Loughborough so not too far from you. https://www.ebay.co.uk/itm/125754371195. I doubt you'll get a transformer any cheaper than the cost of the scrap set, unless somebody on the Forum has got one to give away.... You would get a set of spare valves to boot. Cheers, Jerry

[PJL]

I wonder if the mains transformer has been completely bypassed? we need to know where the grey resistor from pin 2 is going to. I suggest you take up Cathovisor's offer.

[DMcMahon]

From Post 10.

David

[Cathovisor]

Hi Brian,

you have a PM.

[BrianAllen]

Good evening all,

I have now removed the transformer and will set out all of the stray/cut wires, so you can see the alterations made by previous owner/owners.

I appreciate your time and has been a good "learning curve" for me today, thank you.

Brian

[Cathovisor]

Here's two photos of an unadulterated transformer:



So I think if we compare the original with these, we can see where the cuts are.

At the moment, the transformer is sitting on a radiator warming through because currently (no pun intended) I can see a leak between primary and secondary of about 4 MΩ which is clearly no good: as I said before, it has literally been outdoors. I don't think I've got any more AC11 chassis as scrap either, unless I go down the route I was planning of which was to replace the chassis in a surplus AC11 I own to produce a super-powered set with twin loudspeakers... so let's see.

[BrianAllen]

Thanks Mike.

Clearly a quick fix I have to get the set up and running.

There was only one connection to the voltage selector.

As you will note from the pics, wires have been cut/bypassed both on top and underneath the transformer.

Brian

[Cathovisor]

That does look like it's had a burn-up

Today I quickly put my meter on the transformer I removed from my scrapper and it seems the inter-winding leakage has gone: I'll leave it on the radiator over the weekend and then do the tests I mentioned in my PM to you.

I am cautiously optimistic

[BrianAllen]

Thank you Mike.

Please tell me more about the super powered set with twin speakers; sounds interesting.

Brian

[Cathovisor]

Originally Posted by BrianAllen

Thank you Mike.

Please tell me more about the super powered set with twin speakers; sounds interesting.

Brian

Okay: the metalwork of the AC11 bears a striking similarity to that of Bush's contemporary console, the SUG26: this had push-pull output driving a 10" loudspeaker.

If it fits, I have a surplus AC11 to which I would fit the SUG26 chassis into: however, it would also be a good idea to fit a second loudspeaker on the other side of the cabinet which is blank at the moment.

Thus I would have an unassuming-looking set that could pack quite a punch! I do also have a SUG26 in storage, which needs a correct mains transformer fitting (it has a replacement). The SUG26 was Bush's last set with push-pull output for the domestic market - the export market got the EBS/EU44 which had push-pull output in a large table set. Some of these were sold on the domestic market too.

[Herald1360]

Originally Posted by Cathovisor

.......

I do also have a SUG26 in storage, which needs a correct mains transformer fitting (it has a replacement). The SUG26 was Bush's last set with push-pull output for the domestic market - the export market got the EBS/EU44 which had push-pull output in a large table set. Some of these were sold on the domestic market too.

Last valve set presumably? Hardly any transistor sets save early car radios were not push-pull output.

[Aubade65]

Regarding your damp spare transformer.

You may want to consider a technique used by some of the tv restorers who put a low voltage dc current through the LOPT eht overwinds to dry them out - it is supposed to improve the subsequent reliabilty no end.

Have not tried it myself but it would seem that if sufficient heat was generated by the current then it would tend to dry out from the inside.

[Cathovisor]

Originally Posted by Herald1360

Last valve set presumably? Hardly any transistor sets save early car radios were not push-pull output.

I ignore transistors as the work of Satan.

[Cathovisor]

Originally Posted by Aubade65

Regarding your damp spare transformer.

You may want to consider a technique used by some of the tv restorers who put a low voltage dc current through the LOPT eht overwinds to dry them out - it is supposed to improve the subsequent reliabilty no end.

Have not tried it myself but it would seem that if sufficient heat was generated by the current then it would tend to dry out from the inside.

Once upon a time - thirty or so years ago - I did consider using a 6V 50A linear PSU I owned to connect to all the AC sets I had stored in my garage to in order to do just this, but as a preventative measure. I have indeed considered it in this case but wondered about any potential magnetising effects on the core? Probably totally wrong but that may also be tried in addition to the radiator.

[BrianAllen]

What are LOPT eht overwinds?

[Cobaltblue]

Originally Posted by BrianAllen

What are LOPT eht overwinds?

LOPT is the Line Output Transformer in CRT TV.

The overwind is the bit that recovers the energy during flyback to generate the EHT needed for the CRT.

Cheers

Mike T

[BrianAllen]

Thanks Mike.

Brian

[Radio Tech]

If that were me I wouldn't have a bodge like that, it would be better to try and put it back to how it was manufactured , a lot safer and would not be a potential dangerous situation.

Ken