Equipment and safety help please

[dazaaa1]

So, I am a complete novice when it comes to radio. I can just about use a multimeter and I understand volts, ohms ect. I am really excited about getting an old radio to play with but I don't want to dive in to somthing that could potentially go bang. So, I am asking for any advice regarding basic testing equipment, and also what to look out for so I don't hurt myself. I would also like to know what an isolating tansformer does.

Any help is really appreciated.

Regards
dazaa

[G8HQP Dave]

Old (valve) radio sets use lethal voltages, so be careful what you touch! As far as possible, do things with the set switched off and unplugged. Some adjustments have to be made while the set is operating, so be careful - some people advise keeping one hand in your pocket so any shock can't leap across your chest (where you heart is) from one arm to the other.

Unless you know for certain that an old set has recently been in use, don't just plug it in and switch on - you may cause the electrolytic capacitors in the power supply to explode! Check for any signs of overheating, bulging, electrolyte leakage or corrosion. If it all looks OK then power up carefully via a Variac or lamp limiter. You may need to 'reform' the electrolytics.

Get a circuit diagram of the set (available from this website). Learn to recognise the major components, and the likely circuit stages- especially if you can't find a diagram for it.

Tools: essential - multimeter, assorted screwdrivers, soldering iron (15-25W i.e. not too big, not too small)
very useful - RF signal generator, oscilloscope, a working radio
sometimes useful - frequency meter

An isolating transformer provides mains voltage but at a higher impedance and isolated from the mains itself. This means that you can work more safely on an AC/DC set, which does not have its own transformer. The HT supply voltage for the valves is still dangerous, but at least the metal chassis itself won't kill you.

There is lots of information on the web, both generic and for particular sets, so do some searching and reading. If you are fairly new to radio, it might be safest to start with transistor sets from the 60's or 70's, rather than valve sets from the 40's and 50's as the voltages are lower so much safer. Or start by bulding a crystal set - you can learn a lot about tuning, impedance etc.

[Nickthedentist]

Paul Stenning, the owner of this forum, has explained it all here for you: http://www.vintage-radio.com/repair-...ion/index.html

Read it all. Don't worry if it doesn't make sense first time round. Ask if you get stuck.

An isolating transformer is a nice luxury, but an RCD is cheaper and possibly of more value, (and your sockets may already be protected by one in your fusebox).

Good luck,
Nick.

[Station X]

There are very few faults on a vintage radio which can't be fixed with nothing more than a multimeter. Don't buy signal generators, scopes, valve testers etc. until you actually need them.

[paulsherwin]

There are differing opinions regarding isolation transformers. Their main advantage is they allow test equipment to be connected to AC/DC live chassis sets, and they are practically essential when working on old TVs.

The safety benefits are more arguable though. You can work on an AC/DC set safely without an isolating transformer, but you must ensure that the chassis is connected to mains neutral, and recheck whenever you've carried out significant work. You need to actually check the chassis isn't live with a mains tester - it's not unknown for mains sockets to be wired the wrong way round.

An old repairman's trick is to keep one hand in your pocket whenever working on live equipment. This ensures that any shock isn't across your chest (the most dangerous type) and makes any powerful shock much less likely. You can also wear latex gloves while working, but don't rely on these as a primary means of insulation and don't be lulled into a false sense of security.

Paul

[dazaaa1]

Thanks for all the advice guys. I am amazed at the simplicity of crystal sets. I have noticed afew new kits on ebay but there is a vintage kit which looks quite good. I am interested in buying it but is there anything that I should look out for? I am guessing that being a vintage piece it will require small repairs. The best bit of crystal radio's is that there is no electricity envolved so I am completely safe

Or does anyone out there have a better suggestion than a vintage xtal set?

dazaa

[Sideband]

Well I don't know about a better suggestion but certainly an alternative to get the feel of radio is to perhaps start off with a simple crystal set and then progress to a few simple transistor circuits (low voltage again) but remember that todays MW band is a lot different from that of 70 years ago!

To get a simple crystal set to work reasonably well you will need a long aerial...75 to 100 feet would not be unusual and in most areas you will be restricted to local stations as most if not all the nationals have moved off. Don't expect to receive more than two or three stations either. However when you get a simple crystal set working, it is still a delight and soon you'll want to improve it.

A simple transistor amplifier could give you loudspeaker reception from it and then you'll want to progress to something more advanced with better selectivity and a ferrite aerial. There are a number of reflex transistor circuits on the Web using two or more transistors and these can give very impressive results from fairly simple circuits.

This is more-or-less how I started but it was easy back in the 60's to get surplus components and build up stocks of parts very cheaply. I always had the greatest fun with valves though and when I progressed on to more advanced stuff like superhet shortwave sets I found it much easier to get good, stable results with valves and, of course, they are much more forgiving than transistors if you make a mistake and short something out....!

Whatever you decide, it's all about having fun with the technology.

Anyway having drifted off topic somewhat because the thread was originally for equipment and safety, the minimum you need is a good soldering iron and a testmeter. You don't need fancy bits of kit at the moment as they would only confuse. Isolation transformers are handy but not essential. Ebay is a good place to look but really you only need fancier equipment as you progress. Most hobby radio needs are met by a soldering iron and a meter. It's up to you if you choose analogue or digital. Personally I use both and use either depending on what I am doing/checking. You don't need anything that breaks the bank and Maplins is as good as anywhere for getting what you want.

As you progress, you'll know what you want and look on eBay or go to swapmeets. A signal generator is good to have but not for starting out and a scope is a luxury for most and not really necessary for radio work but, of course, at some stage you'll want a telly and then....!



Rich.

[paulsherwin]

If you want to start off building simple transistor based radios to learn the ropes, there are lots of 1960s and 1970s projects here: http://vintageradio.me.uk/radconnav/transtrf/

If you have trouble finding modern equivalents for the transistor types listed, just ask here. In general, any modern small signal silicon transistor can be used in these projects if they specify something like a BC108 or BC109. Modern silicon PNP types can usually be used if the circuit specifies OC44s or AF117s.

Paul

[wireful3]

Starting with a crystal set is a very good idea because as you say they need no power supplies and are safe but I would not recommend a vintage one a starter for two reasons:- First they use a cat's whisker and crystal. Finding the sensitive spot can take a lot of time and over-ride any other problems. The second reason is that they are usually very collectable and so expensive. Mistakes working on these are a bit distressing.

More recent sets using crystal diodes are easier to work with but perhaps not as satisfying. As has been said by others, building one from scratch with modern components gives a good understanding at very low cost.

Early transistor battery portables are a good start for the full blown fault finding. They are safe and some are very cheap, so not a lot is lost if you make a big mistake. Simple tools, a soldering iron and a multi-meter usually suffice.

[Radio_Dave]

I started with nothing more than a multimeter, series lamp limiter and soldering iron.

I would advise your first restoration be done, as much as possible, with the power off. Do a blanket change of tubular capacitors and for the sake of safety and piece of mind, change the electrolytic smoothing capacitors.

When it comes to powering up use the lamp limiter (see here http://www.vintage-radio.com/projects/lamp-limiter.html ) If you need to take voltage readings, connect the multimeter with crocodile clips before turning on

If you want to talk about crystal sets etc, you really need to start another thread

HTH
David

[dazaaa1]

Thanks for taking the time to help me out. I have had a good look around and found one very simple crystal set on here:
http://vintageradio.me.uk/radconnav/crystals/
It is the 3rd one down.
The only problem I am having is working out what I actually need. Obvious bits are the base, block connector and wires but I don't get the whole thing about the capacitors. Are the bits reqiured availible from maplins or are the only availible online?

I really appreciate all the help from you guys.

Regards
dazaa

[Darren-UK]

Within this thread is described the purpose of an isolating transformer. This has largely been in the context of a seperate piece of safety equipment connected between the mains supply and the radio or whatever.

You should also be aware of transformer types found as integral components on radios and other equipments. On AC mains only equipment, this will usually be an isolating transformer. You've asked about safety; knowing from the start which chassis' are potentially dangerous and which are less so would be a good idea. You will need to learn to read circuit diagrams and to start you off I've attached part of a circuit diagram showing the symbol for a mains isolating transformer.

To help you learn about reading circuit diagrams you can begin a seperate thread in the I&SDW section. Remember that, apart from if you fiddle around with a crystal set, you'll need to learn this from day one.

On the subject of crystal sets, I'm inclined to say don't bother for reasons given within this thread. All you'd learn from a crystal set is what a coil does and the characteristics of a radio signal. You could learn that in five minutes by reading a book, searching the internet or even asking in the forums.

My advice is to obtain some tatty old transistorised receiver that does not use modules or IC's. Then obtain the service data, study that and familiarise yourself with the various stages of the radio and what they do/how they function. Learn about the RF stage, the IF stage, the audio and output stages of Superhet receivers. The forerunner of the Superhet was the TRF (Tuned Radio Frequency) receiver; whether or not it'd be worth your while learning about those first I wouldn't care to say.

So if you fancy learning initially from a transistorised receiver, I suggest getting hold of a cheap (probably with cabinet damage) Bush TR82B or C. These have a metal chassis with most components clearly visible and accessible and thus easy to understand when you have the circuit diagram in front of you too.

Having then learnt how a radio receiver functions, you can then look at promoting yourself to a valved receiver. I'd suggest considering a battery-valve receiver then, once your ok with that, consider further promotion to a mains powered valved receiver of the AC-only configuration.

With a battery-valved receiver you're free of the hazards of mains electricity and, beyond the power supply, a battery receiver is essentially the same in principle as a mains powered one. This would also teach you about LT and HT (Low and High tension) circuits. Look for a 90v + 1½v (90v High Tension, 1½v Low Tension) receiver, for which you'd need to make up a power supply. You can actually start learning now - work out for yourself how to make up those power supplies.

So there's a few more suggestions for you. A lot of this is no doubt baffling for you and may even appear off-topic, but it isn't. You've asked for equipment and safety help, fair enough, but you do need to learn from the very basics upwards before you can even begin to understand about equipment required, why and what you need/don't need. Same goes for safety; you need to learn from the basics upwards to understand the safety issues and how to put them into practice.