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Old 20th Jul 2014, 5:06 pm   #81
Andrewausfa
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Default Re: Ambassador 545

Nice one, well done! It's a great sense of achievement isn't it?

Now, you can't call it job done yet though. Is anything getting hot that shouldn't be, like that large can holding the 8+8uF capacitors or the transformer? The transformer might get warm but shouldn't be hot. Remove mains plug before checking. Which components did you end up replacing?

Andrew
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Old 21st Jul 2014, 6:51 am   #82
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Default Re: Ambassador 545

Thanks Steve, Andrew,

Just so chuffed to see it power up, I felt like Dr Frankenstein: "It's Alive!!!"

I realise I still have quite a way to go, but felt confident enough to give the set a try.

Andrew,

I just followed everyone's advice on here and replaced all the wax/paper capacitors, the electrolytic capacitors, and several of the resistors.
Also, cleaned off a lot of the gunk and re-insulated quite a bit of the wires.

Really enjoyed working on the set, just took my time.

Thanks again, everyone, for getting me to this stage.
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Old 25th Jul 2014, 10:29 am   #83
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Default Re: Ambassador 545

Can I ask a really basic question, please?
Can anyone point me in the right direction of how to correctly use the multimeter?
A link or your advice would be appreciated.
I aren't sure I am using it properly when checking the capacitors and/or resisters.

Thank you in advance.
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Old 25th Jul 2014, 10:54 am   #84
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Default Re: Ambassador 545

A bit American, but try this for a start...

https://www.youtube.com/watch?v=bF3OyQ3HwfU

Cheers,
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Old 25th Jul 2014, 10:56 am   #85
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Default Re: Ambassador 545

Firstly, when checking the resistance of any component it is best if it is out of circuit. So for a normal, two leaded component such as a resistor or a capacitor, one end (only) of the part needs to be disconnected from the circuitry. For checking resistors, set your meter to measure an 'Ohms' scale and apply your test leads to each end of the resistor then adjust the range knob on the meter until a reading is seen - preferably around mid scale - but try to avoid readings at the extreme ends of the scale as you'll have trouble making an accurate reading.

For 'middling' caps of around 0.1uF set the scale to read its highest resistance values and fix your eye on the needle (digital meters are not so good for seeing this effect) and at the point of contact of the leads to the cap you should see a slight movement or 'kick' of the needle after which the resistance should be infinitely high. If a resistance is measured in this 'steady state' (after the kick) then the cap is leaky and generally needs replacing. For lower value caps such as pF range mica ones, you will not see this slight movement of the needle but the resistance should still be infinite. For electrolytic caps put your negative meter lead to the positive connection of the cap and the positive lead to the negative cap connection and - like in the first example - you should see (a more positive and obvious) movement of the needle, then the needle should move the other way towards infinity as it becomes charged. For higher value caps - say of 4uf upwards - this movement will be quite slow and very 'viewable'. Depending on the age and/or the charged state of the electrolytic cap the resistance should settle at infinity or several megohms.
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Old 25th Jul 2014, 12:37 pm   #86
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Default Re: Ambassador 545

Brilliant, guys, both of your posts are just what I needed.

Many thanks!
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Old 9th Aug 2014, 7:52 pm   #87
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Hi Everyone,

Been on holiday for a fortnight so haven't had chance to work on my radio, but the work I did today has resulted in a deafening silence!

I have been replacing capacitors C24 & C25, and immediately realised there were three 'pins' from the bottom of the silver case, once coloured yellow, one red and the third black. I have presumed the black pin is a 'negative terminal' for both capacitors? Am I correct?

Also, is anyone able to take a look and the drawing of my Ambassador and clarify how the capacitors are wired into the set, please?
I have tried following the drawing but have obviously incorrectly soldered something, as the set is not silent (only a hum from the speaker - it doesn't tune anymore).

Thank you in advance for any advice/help offered.

Gray
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Old 9th Aug 2014, 8:08 pm   #88
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Default Re: Ambassador 545

Quote:
I have been replacing capacitors C24 & C25, and immediately realised there were three 'pins' from the bottom of the silvers case, once coloured yellow, one red and the third black.
I have presumed the black pin is a 'negative terminal' for both capacitors?
Am I correct?
I think that's been answered in post #27.

If you're fitting a new can the common or negative connection will be labelled as such.

If your using two separate axial or radial lead capacitors there'll be an arrow with a lot of - symbols pointing to the negative leads which should be connected together.
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Old 9th Aug 2014, 9:08 pm   #89
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Default Re: Ambassador 545

HI Graham

Thanks for your reply, I have used two separate capacitors and have linked the negative ends, so at least I have that bit right.
My mistake must be the rest of the soldering but I am struggling to follow the drawing (in order to check my work properly)!
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Old 9th Aug 2014, 9:26 pm   #90
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Default Re: Ambassador 545

I assume by "drawing" you mean circuit diagram. A circuit diagram doesn't show the physical routing of wires or location of commoning points. This would render a circuit diagram difficult to understand. Think of it as being more like a tube map rather than an OS map.

You should have made a note of where you disconnected the capacitor leads from, or better still taken photographs. If you haven't done this then you'll have to work it out from scratch. I assume the can was connected to chassis? If so that's the two negative connections taken care of. C25 pos will go C26 pos or L13 or L16 or L18 or V5 heater, probably whichever is physically nearest. There are any number of points on the HT line where C24 could go to.
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Old 10th Aug 2014, 5:17 am   #91
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Default Re: Ambassador 545

Ok, Graham, thanks for your patience.
I came back off holiday, dived in, and am now paying the price.
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Old 10th Aug 2014, 8:26 am   #92
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Default Re: Ambassador 545

We all do that sort of thing! Learning isn't a smooth process, it comes in lumps.

A bit back you were advised, when testing electrolytic capacitors to connect the positive lead of your multimeter to the negative lead of the capacitor and the negative lead of the meter to the positive lead of the capacitor.

I expected you to query this because it sounds odd.

There is a quirk in almost all moving-pointer multimeters that the designer could save switch complexity if the ohms ranges circuitry let the internal battery drive the positive test lead terminal on the multimeter in a negative direction.

For added confusion digital multimeters on their Ohms ranges usually get this polarity right.

It might not always make an obvious difference in readings on an electrolytic capacitor, but it is good practice and it stops you forming wrong conclusions when it did make a difference. On the other hand, knowing the polarity on Ohms is essential when you use it to check a solid state diode.


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Old 10th Aug 2014, 6:52 pm   #93
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Default Re: Ambassador 545

Thanks David,

I have got the radio up and running, phew, but that leads me to a couple more questions!

The radio has three 'tuning' options - Ranges 1, 2 & 3.
I am presuming that equates to LW and 2x SW bands?

Also, the transformer: I took a good look at it today and it is not what I am used to seeing in power supplies!
It appears to be layer upon layer of a paper-type substance, with the power lead sandwiched between them.
A mate was round earlier and I showed him the set and he said "Cut the flex inside the cabinet and use the plastic screw-down, wire connectors to attach a new flex".
Is that what you guys would do!?

It certainly would make the job easier for me!!
But is it right/safe?

Last edited by sooperrio; 10th Aug 2014 at 6:53 pm. Reason: spelling
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Old 10th Aug 2014, 9:44 pm   #94
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Default Re: Ambassador 545

I personally wouldn't use chocolate block to attach a new mains lead.

It isn't clear from your pictures whether the mains transformer wires are brought out to tags or wires. If the former solder your new leads to the tags. If the latter the wires may well go to a tag strip where they connect to the mains lead.

EDIT. Having looked at the circuit diagram It appears that one side of the mains lead goes to the OFF/ON switch and the other to the voltage selector, so connecting to the mains transformer may not be necessary.
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Old 10th Aug 2014, 10:09 pm   #95
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Default Re: Ambassador 545

Attaching a new lead to the remains of the old inside the machine isn't ideal, because some of the ancient lead is still being used. Also, it's introducing another set of connections which could fail, and it looks amateurish.

I would bite the bullet and do the job properly if you feel able.

Nick.
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Old 11th Aug 2014, 6:24 am   #96
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Quote:
Originally Posted by Station X View Post
It isn't clear from your pictures whether the mains transformer wires are brought out to tags or wires. If the former solder your new leads to the tags. If the latter the wires may well go to a tag strip where they connect to the mains lead.

EDIT. Having looked at the circuit diagram It appears that one side of the mains lead goes to the OFF/ON switch and the other to the voltage selector, so connecting to the mains transformer may not be necessary.
Thanks Nick and Graham for your advice.
Looking at your suggestion, Graham, what do you mean by a 'Tag'?

Also, could you expand on your 'EDIT' point please!?
By expand, I mean really simply spell out your advice!
Apologies for being dumb!
Thank you!
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Old 11th Aug 2014, 8:38 am   #97
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Default Re: Ambassador 545

Tags are metal terminals designed to have wires wrapped around them and soldered. They come in quite a few forms. Under many radios you'll find Tagstrip, a length of SRBP composite insulation material with a row of terminals riveted to it. The terminals may stick out sideways and be pressed shapes having loops for the connected wires and components to anchor onto. Turret tags are round and stick up from the insulation like mini castle towers.

Some components have tags as well. Valve holders let the valve plug in on the top and have a ring of tags sticking out underneath to take wires and wire-ended components.

Transformers often have rows of tags for the connections to their windings. Cheaper ones may have wires coming out right from the inside of the winding stack. Switches often have tags for all their connections.

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Old 11th Aug 2014, 9:32 am   #98
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Default Re: Ambassador 545

Quote:
Originally Posted by sooperrio View Post
Also, could you expand on your 'EDIT' point please!? By expand, I mean really simply spell out your advice! Apologies for being dumb! Thank you!
I think Graham just means that neither core of the mains flex actually goes directly to the transformer. Rather, they appear to go to the voltage selector and the on/off switch first. So to replace the mains flex the "proper" way, you probably won't have to solder wires to the transformer at all.

If it's too daunting though, your friend's suggestion isn't unreasonable at all, so long as the stub of flex coming out of the chassis seems in excellent condition and so long as you can anchor the new flex securely; you could rob a plastic "saddle" cord grip from a mains plug and use that to clamp the new flex to the cabinet floor using suitable thin, short screws.

N.
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Old 11th Aug 2014, 10:31 am   #99
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Default Re: Ambassador 545

Nick is correct in his interpretation of my edit point.

If you resort to using chocolate block I suggest you tin the ends of the wires to give the screws of the block a better grip. By "tin" I mean apply solder which will wick into the strands of wire making one solid mass. You'll often find this done on the mains leads of appliances which aren't fitted with a moulded on plug.
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Old 11th Aug 2014, 10:45 am   #100
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Default Re: Ambassador 545

I was always taught that tinning stranded wire which was then fitted to a screw-terminal was utterly deprecated - the problem being 'cold flow' in the solder.
If I find any such tinned-strands-to-a-screw-terminal in stuff I'm certifying - it won't even be allowed to taxi, let alone fly.
If you want to neaten up stranded wire before fitting to a screw-terminal, crimp on a "bootlace ferrule".
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