Ambassador 545

[sooperrio]

Thank you, Livewire

[stevehertz]

I pretty much agree with Livewire, but just to be on the safe side I'd buy 6W resistors, 2W could be cutting it fine. Don't forget that the tolerance on old resistors was - even when new - something like +-20%, and when much used and with 'drift', often much more than that. So, get the 220 Ohms one, and get a 470 and a 390 Ohm one which daisy chained will be 860 Ohms. Alternatively, and perhaps easier is to get a 14W 820 Ohms.

[Andrewausfa]

Originally Posted by sooperrio

I need to replace three resisters that have over heated. On the system data, one is rated 220ohms, the other two, which are daisy-chained together, 440ohms each.

I've been following this thread but getting a little confused here. Just to be clear, do you believe that these two large red resistors are 440 ohms each? Are these the two you refer to as being 'daisy-chained together'?

Andrew

[Herald1360]

Looking at the circuit, there should be a 440ohm and a 22ohm in series between the mains TX secondary centre tap and chassis. The midpoint of these resistors provides a bias / agc delay voltage which is negative to the chassis. The only 220ohm resistor is the cathode bias resistor for the output valve.

The 220ohm resistor needs to be at least 1W type, the 440ohm one at least 3W and the 22ohm only 1/4W.

If you get three 220ohm 2W types you can use one for the 220ohm and two in series for the 440ohm. The 22ohm can be a 2w type just for appearances If you make them all 3W wirewound types they'll be bombproof.....

[sooperrio]

Thanks for your advice, I don't know what I would do without all your help!

"A little (or none at all) knowledge is a dangerous thing", never has this been more applicable than to me.

[sooperrio]

Hello Everyone,

Me again, please can I ask for help?

I am struggling to identify what the blown 'end' of the capacitor on the attachment is connected to!
Can anybody advise, please?
I can't make head nor tail of the system data.

Thank you!

Graham

[Andrewausfa]

Hi Graham,

The capacitor in question is C27 on the ERT sheet you downloaded. It sits across the Live and Neutral wires after the mains switch. If you do replace it, not necessary at this time, the replacement should be an X2 type capacitor. As Chris mentioned early on, it's listed on the ERT sheet as an electrolytic but it is not.

I think I spot the end of C27 that blew off

Andrew

[sooperrio]

Thanks Andrew. for taking the time to reply, great advice for me.

However, I am struggling to find a 10nf 1000V X2 cap on Cricklewood's website.
This is the nearest I can find, would this be suitable, please?

http://www.cricklewoodelectronics.co...2&cat=0&page=1

Thank you!

[Herald1360]

You would struggle to find a 1000V rated X2! That old cap is 1000V dc rated in an attempt to fit a part that would survive on 240V ac.

The Cricklewood part is fine- it's rated for 275Vac and meets the saffety requirements for direct across the mains use.

[sooperrio]

Thank you, Chris.

PS So sorry for asking what must seem like ridiculous questions to you all!

[Andrewausfa]

Graham,

They're not ridiculous questions, keep asking. Now, your turn to answer one I asked earlier Do you have a safe multimeter? Because you'll likely need one as you progress through the set.

Andrew

[sooperrio]

Hi Andrew

Yes, I have a safe multi-meter.
I bought it especially for this job, though I haven't a foggiest how to use it.
Once I have replaced the capacitors and the blown resisters, I will no doubt be asking you all for help on the next stage.

As a minor aside, I have really enjoyed messing around with the set.
I have never done anything like this before, never used a soldering iron, found it all really therapeutic.

I would love to continue with this hobby, I guess I just keep my eye open at car boots for old radios...?

[sooperrio]

Quick question regarding the cord that is connected to the tuning mechanism, does it matter what type of 'string' I use?

['LIVEWIRE?']

Nylon Dial cord, in two different thicknesses is (was?) available from Savoy Hill Publications, whose contact details I've mislaid, but they can be found via Google. There may be other stockists of the correct cord, too.

[sooperrio]

Thank you.

[stevehertz]

Originally Posted by sooperrio

I would love to continue with this hobby, I guess I just keep my eye open at car boots for old radios

Yep, just keep an eye open in back street second hand and 'junk' shops whenever you visit a new town or village - make some cards and leave them with shops. But don't get carried away with your purchases, a lot of shop owners believe that any old wireless is worth good money, they're generally not, especially if they're the more bland 50s ones - not wanting to hurt anyone's feelings who collects 50s sets of course - but usually a tenner or something like that is the going rate. Always check to see if they're complete though, and assess how difficult it would be to get a major part for a set that's only worth a tenner or so anyway? Also, we probably all made the mistake of buying 'anything and everything', well try your hardest not to do that just because you've discovered this old radio.

Also, I'm not sure how successful you'd be now, but many years ago when I first started I used to place wanted ads in the free local newspapers and that brought lots of results. The problem is, there was a heyday in old sets becoming available. In the 70s and 80s, of the people who passed away, there was probably a good chance that there would be an old wireless set in the house that would find it's way into a second hand shop or to a relative. These days older people probably have an 'all-in-one' hi-fi stacking system or something like that! Also, unless you have a specific interest, best to avoid battery sets as you'll have the problem of making or buying a battery converter. Unless you just want it for its visual appeal - nowt wrong with that if you've got enough working sets. I mean, I don't stash sets away under beds and in wardrobes any more, I got to thinking what's the point in having a hidden museum just for the sake of ownership? So, maybe consider getting a working set per room or something like that?

FYI:

50s sets generally have smaller, clear 'glass' valves, and speaker grilles are more often than not expanded metal mesh.
30 sets have larger 'British based' valves that are often painted gold or silver - though very dusty and darkened now, and speaker grilles are quite often cloth covered.
A good book with lots of photos is 'Radio Radio' by Jonathan Hill.
The BVWS is a good society to join, swap meets etc.

[sooperrio]

Thanks for taking the time to write this, Steve, great advice and tips.
Will look at signing up to BVWS!

[stevehertz]

And don't forget - and I'm not trying to frighten you - when working on a 'live' piece of electrical equipment, you are dealing with potentially lethal voltages. Be very careful at all times. The biggest mistake I have made in the past when working on a 'bare' chassis is to switch it off using its on/off switch, but leaving it still connected to the mains. At some point you come back to the chassis, start fiddling with it and inevitably, at some point you touch the mains.. It hurts and it can kill. Moral to the story, don't use the on/off switch when working on a bare chassis, always unplug it from the mains. In fact in those circumstances ie working on a bare chassis, it's best to leave the on/off switch 'on', so you will see by way of scale lamps etc that it is on. Otherwise, as I say, pull the mains plug.

[sooperrio]

Thanks Steve,

I really appreciate your warnings.
Not got to powering the set up yet, am still working my way through the capacitors & resistors, but I must say I am very apprehensive about 'flicking the switch'.

When I get to that stage, I will need some further guidance from you all please.
The flex looks really naff, it is an old corded type.
I have already been advised on this forum to replace it, so I have bought a new flex, but I will need help attaching the new flex etc..

Cheers again

[sooperrio]

Also, this is another silly question, so apologies again, but, I was thinking...

If a capacitor stores a charge, and I plug the set in to the mains, then unplug to carry out some work, will the capacitors still have a charge in them (I am thinking like a battery stores a charge).

If this is correct, do I have to be wary of getting a shock from a capacitor, even after the set has been unplugged?