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Old 15th Jul 2014, 2:23 pm   #61
julie_m
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Default Re: Ambassador 545

It depends. Usually, there will be a discharge path for the capacitor, so the charge will disappear within a short while of switching off.

But a certain Law, better known than Ohm's Law around these parts, dictates that this might not necessarily be the case .....

There may be a high value bleeder resistor marked on the wiring diagram, but high values are renowned for going open-circuit. If in doubt, use your meter first. An analogue meter will discharge capacitors while you wait; a digital one won't, so you will need a resistor of about 47kΩ with crocodile clip leads.
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Old 15th Jul 2014, 3:18 pm   #62
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The only caps you need to worry about getting a shock from are the HT smoothing caps, those 8 or 16 uF ones that are rated at (say) 400VDC. So, just a couple or so. Familiarise yourself with them and just don't touch the terminals - although saying that, those terminals will be connected to other points in the circuitry. It's not a big problem, even if you did get a shock from such a charged cap, it would just 'come sharp', it won't kill you. The real danger is that you may snatch your hand away and slice it on one of those sharp corners or edges that live in old wireless chassis'.
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Old 15th Jul 2014, 6:02 pm   #63
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Default Re: Ambassador 545

Quote:
Originally Posted by sooperrio View Post
...I am very apprehensive about 'flicking the switch'.
Hello Graham,

Have you checked-out the instructions for building a "series lamp limiter"?

http://www.vintage-radio.com/projects/lamp-limiter.html

It's very simple to build and should limit the current that the set can pull in the event of a fault. This will reduce the risk of a loud BANG and possible further component damage if you've made a mistake somewhere.

It's not a safety device, so won't make working on a live chassis any safer and since this is connected straight to the mains, do seek further advice if you're unsure about the wiring.

Do join the BVWS; as a member you'll be able to bid at the auction events. Obviously a rare/collectable radio will attract high bids, but a run-of-the-mill 50's set in working order can be secured for a tenner -or even less which is much cheaper than you'll find in flea markets or antique shops.

Good Luck with the project!

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Old 16th Jul 2014, 8:34 am   #64
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Thanks everybody, great support for me and I will definitely build a lamp limiter before 'going live'.
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Old 17th Jul 2014, 8:36 am   #65
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Default Re: Ambassador 545

You don't really have to "build" anything. A redundant bedside lamp with a 100W "traditional" bulb wired in series with your radio's live wire is all you need if you don't intend to make a long-term hobby of radio repair.
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Old 17th Jul 2014, 9:17 am   #66
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Well he 'kind of' does have to build something, I mean if you plug something into the mains, it's in parallel with whatever else is plugged in. So he has to access the wiring and with safety in mind perform some rewiring, some kind of jig or terminal arrangement to connect the lamp in series. Ok, we're just playing with words (I didn't start it!), but in effect he is 'building' a series lamp limiter. And as the OP has said that he does intend to carry on with the hobby, there's every reason to make it into a easy to use rig with maybe an added (series connected) mains socket on the wireless side; plug and play style.
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Old 17th Jul 2014, 2:23 pm   #67
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My "poor person's variac" (as I first heard the series lamp limiter described) consists of a batten lampholder screwed to a piece of scrap wood; and a short mains extension lead with a BS1363 plug and socket. I carefully slit the outer sheathing about halfway along, for 20cm. or so, using a craft knife; then extracted just the brown wire, cut this and wired the cut ends to the two terminals of the lampholder, leaving the blue and yellow / green intact. Hammered in a couple of cleats to keep the wires from moving about too much, and the job was a good 'un.

You can do a more professional job with several lampholders for different wattages of bulbs and a multi-gang switch; with two bulbs you could have 60W, 100W, 60W and 100W in parallel; and if you used a 3-gang switch, you could even have a "bypass" position for when you feel truly confident.
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Old 17th Jul 2014, 2:47 pm   #68
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Default Re: Ambassador 545

A test lamp has advantages over a Variac in as much as it limits the current under fault conditions.
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Old 17th Jul 2014, 2:50 pm   #69
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Yes, indeed. Even although I do now have the real, rich person's version, there's a lot to be said for the simple lamp limiter -- you can even learn to "read" what is happening from the brightness changing.
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Old 18th Jul 2014, 2:15 pm   #70
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Default Re: Ambassador 545

Really interesting, guys.
I do intend to continue with the hobby, so will look at making a lamp limiter.
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Old 18th Jul 2014, 2:23 pm   #71
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Just to add to my last message, do you know the closer I get to turning the set on, the more I am going to miss working on it!

Will have to get another radio if this project is a success.

Have really enjoyed trying to learn new skills and knowledge.
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Old 18th Jul 2014, 4:08 pm   #72
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Default Re: Ambassador 545

Don't get disheartened if is doesn't work when you first switch on. It's not uncommon.

There are plenty of members here who'll help you to fault find it.
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Old 19th Jul 2014, 4:41 pm   #73
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Thanks Graham, I am already trying to prepare myself for the bang, or absolute silence when I plug the set in!

A couple of quick questions, please.
I noticed on the speaker a label that states 'Goodmans Industries,Middlesex'..is this the same Goodmans that make electric goods today?

Also, I see that there is a big silver capacitor, that is nestled amongst the valves, on the top of the chassis.
How do I check if this is OK?
Using the multimeter?
Or should I just replace it, as I have the other capacitors?
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Old 19th Jul 2014, 4:54 pm   #74
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Yes, it's the same Goodmans - to a degree! Like all of these famous British 'audio' companies, they tended to get bought out by bigger or competing companies. When I worked at Thorn Automation in Rugeley, our factory shop sold all of the brands in the Thorn group, and one of those was Goodmans. I bought a Goodmans Module 90 hi-fi system. These days Goodmans is owned by Harvard (previously Alba - another old British Wireless company) and they sell all manner of budget domestic audio products that are erm.. made abroad. Harvard also owns Bush, another wireless manufacturer from the past. But essentially, yes, there is a paper trail from your Goodmans speaker to the set top boxes of today.

TBH, I'd replace any cap that is electrolytic or waxed in that set.
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Old 19th Jul 2014, 9:48 pm   #75
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Thanks, Steve, for your reply.

So, do you all look fondly at any electrical equipment today that is badged 'Goodmans', 'Bush' or 'Alba', because of it's links with wireless of the past?
Do you all have a favourite manufacturer?
Is there one above all else?

Also, regarding my set - I've hit my first night of frustration.
I have had to walk away from the radio without achieving my task: attaching the 'tuning cord/string'.

First of all, I am guessing which end of the tuner scale the pointer should start (I've gone for low number on the disc that is numbered 0-90 means the pointer should be at the lowest frequency on the station display), and secondly, actually threading the cord, getting the tension and then tying it

I have given up for tonight!
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Old 20th Jul 2014, 9:30 am   #76
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Default Re: Ambassador 545

One other thing, if I may ask for help, please?

Can you see the Hunts Electrolytic Capacitor on the attached image?
I think it is C24 & C25 on my data sheet.
But that means there are two capacitors in one silver case...?
Is that correct?

On the Capacitor it says "Red 8uf, Yellow 8uf, 450v DC, Surge protector" and then mentions "Black...", but I can't quite read the rest.

Please can I ask for help in identifying a suitable replacement for this capacitor(s)?
And how would I go about attaching the new capacitor when the old capacitor is in a big silver case that looks like a valve attached to the chassis?

Thanks in advance for any help you can offer!
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Old 20th Jul 2014, 9:51 am   #77
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Default Re: Ambassador 545

Yes, that big aluminium can with 'Hunts' written on it contains electrolytic capacitor(s)

You'll come in versions with one, two or three capacitors in the same can.

You can get replacement double ones if you look around on this site you'll come across references to the BVWS selling them as a service to its members. There is also a German supplier.

The poshest replacement isn't a new commercial dual capacitor. Some people tease the rolled end of the aluminium can open, pull out the rubber end and extract the gooey capacitors themselves from the can. The capacitors are a swiss-roll of two aluminium foils and a soaked paper strip. THe can gets cleaned out and two modern electrolytics get stuffed in the can with appropriate insulation and wiring to the original rubber/plastic end. Modern electrolytic capacitors are dramatically smaller than old ones of comparable ratings. The end of the can is carefully swaged back to hold the end and voila, you have a capacitor which looks just like the original. This keeps your set looking original inside if that is important to you.

The quick and dirty approach is to leave the can in place, and to put the small modern parts under the chassis.

Having two Cxx numbers for two capacitors in the same can is normal.

The black painted tag will be the negative terminals of the two capacitors commoned together.

Usually one capacitor is wound outside the other as a sort of more complex swiss roll. This outer capacitor gets better cooling than the inner, so it's the best one to be used in the circuit position with the greatest ripple current. They'll work either way, but this detail improves the overall life-expectancy.

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Old 20th Jul 2014, 12:42 pm   #78
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Thanks, David, for helping me!
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Old 20th Jul 2014, 4:04 pm   #79
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Wanted to share this with you all...guess who has just been listening to Test Match Special on his Ambassador 545!?

Thank you, thank you, thank you, thank you, thank you.
Each and everyone of you for helping me get to this point.

I have plugged the set in and it lit up and tuned in, wonderful to see it working, my dad would of been so proud.

The only downside is the gramophone turntable is constantly turning, I can't seem to stop it - would anybody have ideas what I have done wrong?

Also, the mains lead needs replacing, so I will no doubt need further advice on this.

But for now, I am going to enjoy the Test Match!

Thank you ALL once more.
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Old 20th Jul 2014, 4:19 pm   #80
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Congratulations! how good is that?! Isn't it so nice when you get your first wireless going?! Yes, change that mains lead, old ones can be dangerous. Sorry I'm not an expert on turntables, but I'm sure it won't be a big problem. Often, the actual motor is always running anyway 'in the background', so it may just be a mechanical issue that whatever arrangement puts it into 'run' mode is sticking on.

And don't forget to pull that mains plug every time you get your hands in that set - unless you're measuring a voltage of course.

Well done, you'll be advising people on here soon!
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