Test equipment for valve radio repair

[Telleadict]

How about making this thread sticky?

A lot of new visitors must have similar questions going through their minds.

William

[Brian R Pateman]

Good thought - thread duly "Stuck"

Regards,

[squinancy]

As an amateur enthusiast who will probably never graduate further may I add my less professional take on this. I sometimes find it hard to replace electrolytic capacitors, the inevitable main culprits. The usual values, 47 + 47 uF, or 100 + 100 uF are often difficult to obtain in the necessary working voltage, 350 - 450 DC. Single Plessey capacitors often fetch a small fortune on eBay. Paper capacitors must also, as a rule, be replaced, but plastic foil caps that do the trick are much easier to come by. Maplin does the whole range. Carbon resistors are replaced with similar ease. As for the electrolyitics, I do not find capacitance meters useless. Sometimes a choice has to be made between a cap from a dodgy source but dated let's say 1989, and a cap made by Plessey in 1965. I always test these, and choose the one which produces the reading closest to the nominal value and which shows the better retention of a DC charge. The latter is a simple test.
Gerry Wells keeps telling me that valves never go wrong. While that is an exaggeration, problems posed by valves are straight issues. I always replace valves which appear not to perform according to specifications. Sometimes this is a costly policy.
Maplin has a 48W digitally controlled heat soldering iron for 30 quid, great value I think. This is what comes to mind in brief. And best of luck.

[majoconz]

IMHO it's not what you have for testing, it's being flexible and realising what you can do and what you can't do with what you've got! A simple diode detector can be added to an analogue multimeter for comparative RF measurements on an oscillator. You can make a simple 'Equivalent Series Resistance' checker for electrolytic C's. (http://ludens.cl/Electron/esr/esr.html) You can use a PLL HF receiver instead of a frequency counter. Make a signal tracer in a small box with an LM386, a PP9 and a small speaker, add the diode detector and you can follow the signal back up the IF strip. Add a couple of sockets across the speaker for your analogue voltmeter and you have a high impedance VTVM. You're only limited by your own ingenuity.

Good luck and best regards - Martin

[kestrelmusic]

I have a useful home made gadget which is very simple but could save a nasty moment. It's a simple neon lamp in a holder on the wall by my workbench. One pole is connected to earth, the other via a resistor to a lead with a test prod. Just poke anything you are proposing to touch with the test prod first...

[Alan Stepney]

One of the less common pieces of test gear is the Grid Dip Oscillator.
Widely used in Ham radio circles, it can also be useful for some types of general repair work.

When coils need rebuilding / rewinding, they are a simple way of getting the inductace right, and can also be used to find the capacitance of low value C's.

[John12868]

Excuse my ignorance, but is a function generator the same as a signal generator?

[ppppenguin]

A simple function generator usually generates a choice of sine, square or triangular waves. The sine waves are often a bit distorted at the peaks. Sophisticated function generators (often called arbitrary function generators) can be programmed to generate any waveform. Most FGs only go up to 1MHz or so. They often go down to fractions of a Hz. Frequency can often be swept over a wide range so they can work as a wobbulator if they go to high enough frequencies.

Signal generators produce sine waves. Sometime also squre waves at lower frequencies. They usually have facilities for amplitude modulation, sometimes FM too.

[Billy T]

I started in electronics as an apprentice 44 years ago and have serviced all kinds of appliances from the usual toasters, heaters & shavers etc, TRF valve radios (from elderly customers) valve TVs, radios and radio telephones of the slightly more modern era, through to all solid-state colour TV, radios, radiotelephones etc. Next to a good multimeter the most useful instrument I ever had was a small battery operated high voltage insulation tester.

In my opinion their value and usefulness is highly under-rated. I still use one regularly and with a choice of 250, 500 and 1000 volt outputs it is surprising how much it can tell you about a lot of components that a multimeter can't. I am not overly fussy about the maximum rated operating voltages for various components either, if they can't stand a test voltage 100 volts or so in excess of their rated working voltage then they are not going to be reliable in service. I recently bought some NOS oil-filled .1uF 1000 volt caps which checked out perfectly with a multimeter but they all leaked a little at 250 volts and a lot at 1kV.

I too prefer an analog multimeter for most servicing and although I own several AVOs of various marks, my meter of choice for general servicing is a Hioki AS100D 100,000 ohms per volt sensitivity and 22 volts at the probes for high-ohms testing. It is a good compromise between the higher loading of a 20k-ohms/V AVO on low voltage ranges and the very high input impedance of digital meters and has a large and very clear scale.

For my business I have a wide range of test equipment including several scopes, signal generators and some other fairly exotic goodies but when it comes to fixing radios, nothing much beats a comfortable seat and a good meter.

Incidentally, I am rather envious of the range of service sheets you have available, because although we did have circuits for most radiotelephones and TVs, and books of circuits that covered most Japanese transistor radios, almost all valve radio servicing was done without the benefit of a circuit, enforced experience that stands me in good stead today.

Cheers

Billy

[Oldtimer74]

HI. Whilst I would agree with almost all the previous comments I would like to add a couple. NEVER switch on an mains wireless that you have no knowledge of or has not been in use recently without first disconnecting the electrolytic smoothing capacitors. You can easily get a BANG and a nasty mess and a requirement for a new rectifier.
Having said that I always try to reform electrolytic capacitors that have not been in use for some time, even new old stock. This is easy to do and I reckon I have had 95 per cent success even managing some wet electrolytics from the 1930s.
You need a DC supply of 250-300V. It should be at the same voltage as the caps are going to be used at but I find if you can only get 250V then they will almost certainly be OK for a bit more.
Connect the cap in series with a 15k resistor and a multimeter, on suitable current range, with corerct polarity across the DC supply. Initial current will be several ma but will quickly drop and in time will eventually settle down at, hopefully a low value. Leakage current is always present in electrolytics but should not exceed (for plain foil types - these are likely to be the earlier ones) 0.15 X cap (in mfd) X voltage, microamps. For Etched foil types it should be 0.5 X cap (mfd) X voltage, microamps This equates to about 1 ma for a 450 V 16 mfd. If the cap is noticeably warm at the end it is probably doubtful.
Good luck
Pat

[Top Anode]

A while back I happened across a brochure for what I suppose was the industry standard scope of the 50s. The Cossor Double-beam. It cost 550 pounds sterling - about a year's wages.

That wonderful thick steel-tube trolley was extra.

[vahakuja]

In the case you'll like to test capasitors (excluding Hunts!) have a look to the link:
http://www.radio-ghe.com/isotest6.plan.htm

IsoTest tester ( by Mr. Heigel) is a suprior tool if you like to repace just leaking capasitors and save as many "original" as possible. Unfortynately this tester is not commeriaclly available but it is not so difficult to make it.

regards
Ake

[mister valve]

I would say the 'must-haves' for Radio (Electrical) restoration's are a High resistance multimeter, RF sig. gen. (optional), and a selection of tools e.g. Pliers, Cutters, Screwdrivers, trimmer tools as well as Soldering Iron & Solder).

On my work bench I have numerous bits of test equipment which spends most of its life just 'dust gathering'. Though it does look 'the business' I suppose !!!!

As mentioned by other restorers.... Basic tools and a multimeter is usually all that is needed.

[Ragazzo_2009]

Indeed, a simple meter is enough for simple tube radio. The story changes, when you try to do something with high tube count device, like old TV set. I got one - made in 1952 - a combination of radio receiver and TV set. 32 tubes. Instead of buying a replacement set, I ordered a tube tester. I also consider it to be a nice vintage device by itself - why not to have it in collection?

[DAVEHALL]

Gents - have posted this elsewhere ( and I'll keep on posting it ,till message gets through) --voltages into a mains set =230/250 v AC ( SO POSSIBLY AS HIGH AS 350V).
Output of DC rectifier - possibly as high as 300v DC .
With a CHEAP meter - do you get leads that are tested up to this sort of voltage , or higher .For most jobs ,I'll make do with a set of leads made from a bit of mains flex ( possibly ok at these sorts of voltages) - I've never had a problem on mains .BUT -do you really want to put your life on the line for a cheap set of leads ? For as little as £5 you'll get a set of CAT111 leads from someone like Maplin (1000v 10A).

[Kat Manton]

Hi,

I'll add what's arguably a 'nice to have' to the list.

I was going to design/build a capacitor leakage tester with several selectable voltages, basically a high-voltage meg-ohm meter, until I discovered a device already existed which does exactly that.

I'd always assumed that insulation testers (usually 'Megger' though there are others) used a fixed voltage, often too high (500V) for capacitor leakage testing.

Then I encountered the Megger BM8/2 - a multi-voltage insulation tester. It's analogue, battery-operated, the internal circuitry is fairly simple (so should be repairable); measures resistance at selectable voltages with ranges as follows:

• 0 to 1,000MΩ at 50V
• 0 to 2,000MΩ at 100V
• 0 to 5,000MΩ at 250V
• 0 to 10,000MΩ at 500V
• 0 to 20,000MΩ at 1000V

(All ranges include infinity of course; the above are the limits of what can be measured on the meter's scale.)

This looks much more useful than a fixed-voltage tester; one of those "why didn't anyone tell me these things existed sooner?" bits of test gear!

They're not particularly expensive as they've been superceded by a digital version, seem to be fairly common and turn up second-hand often enough.

I've just bought one (though I wouldn't class it as 'essential'; in-circuit measurements, substitution and 'on-sight' replacement of certain types have served adequately well so far.) But, given the amount of faulty vintage electronic hardware I've accumulated, anything which helps identify faulty components more readily means I might get more of it working!

Regards, Kat

[boxdoctor]

Just a passing thought......A valve signal generator might be a better bet than a solid state one when working with valves, as a slip of the probe could result in damage to a transistor type, whereas a valve sig genny would just "hold its nose" if a couple of hundred volts was momentarily applied to the output socket. A D.C. blocking capacitor does not necessarily get round this problem, as a cap. has to charge up. causing at least a momentary voltage surge . Usually enough!.

[DAVEHALL]

Originally Posted by Kat Manton

This looks much more useful than a fixed-voltage tester; one of those "why didn't anyone tell me these things existed sooner?" bits of test gear!

And, some of the newer meggers as well as having as above, also have a voltage function as well - useful if you have a DVM (or AVO) and need to use a voltmeter/ammeter at same time.

[peetleetech]

Everybody above is correct, however the most often used item is a soldering iron and the king is a Weller. It is isolated(for those times you are working with power on) and the tip lasts. A good high impedance multimeter is essentual. The AVO 8 is tough and robust but I don't know if it has such a high impedance. Detuning when measuring is a pain and AGC circuits are easily affected. A good signal tracer is easy to build and will trace from the front end to the last AF stage easily. It will test the filaments(hum), oscillator(hiss) and if you can hear the signal in the IF stage then the fault could be the detector, ect.

Billy, I am so envious of you, the AS100d is a beatiful meter. Mine got stolen and I have never got over it.
Peter.

[Skywave]

Originally Posted by peetleetech

. . . however the most often used item is a soldering iron and the king is a Weller

You know, I used to think that too - until I acquired a 'Metcal'; once used, no going back!

However, this is now getting OT: we're talking tools; the Thread is "Test Equipment".

Al. / Skywave.