Roberts Valve & Circuit Analyser

 

 

Roberts Valve & Circuit Analyser

Another antiquity from my loft, given to me by the son of the engineer who once actually used it.
 

Cast you mind back to the TV and radio sets of the late 1940’s early 1950’s
There was no circuit board unplugging and replacing with a known panel back then

Most of the electronic products of the post war era were built on a steel chassis 16 gauge or 1.6 mm thick, 

with a dozen or more valves (tubes).  They were point to point wired with the occasional tag strip

There was no way a service engineer on a house call could take out the chassis to take voltage measurements, sometimes on console models it took two people to carry the set to the van.

Only simple Valve replacements were conducted in the home
Faulty sets were taken to the workshop
Where an engineer would narrow down the fault to an area

Which is precisely where the Circuit tester comes in handy?

Here is the tester in a Classic post War Pressed steel case

With 4 external toggle latches & leather carry handle

The instrument

Showing 2 panel meters 1 current & 1 voltage- Resistance

With selector switches to alter the range of the two meters
The main switch selects the Valve (tube) electrode you wish to measure

Inside Cover picture 

                                              

 Showing Umbilical Cable and a range of valve (tube) sockets, some missing

Operation

Imagine a set with no sound, start by removing the sound output Valve (tube),
Plug the tester umbilical cord into the tester, top left marked “Adaptor”
On the other end of the tester umbilical cord fit a suitable valve (tube)  pin adapter to suit the Valve you’ve removed.

Plug that valve adaptor in the Sets now empty Valve (tube) Base
While plugging the original valve (tube) you’ve removed into the correct socket on the tester

Switch the set on and hey presto   
Read the voltages on each valve pin and compare readings taken with those marked on circuit diagram

Note

There was a small internal battery to power the Resistance Test
Separate Voltage & current tests could be conducted with flying leads connected to the three Insulated Thumbscrew Cable Terminal posts
Marked Amps +,  Volts/ohms +   and Neg

This in now in my collection, my thanks go to Ewart , RIP

Vintage “ALTHAM” Capacitor Analyser

This has been lying around in my loft for over 30 years It’s marked “ALTHAM” and states its “Made in England”
Which is possible, however it has striking similarities to the US made SOLAR Capacitor Analyser from before WW2

 

 This is an internal view  

 

 

Here is a link to the Manual  for  the  SOLAR Capacitor Analyser

 

What does it do?
In the days of Radio Valve (Tubes) circuits using hundred of volts it was  used to test a Capacitors value and the capacitors leakage across the plates

 

Let’s take you back to the fundamentals of a Capacitor in easy terms 

 

A capacitor has 2 metal plates of X area with a gap D between them
We can consider a capacitor as a bucket which we can pour in Electrons
Then pour them out when we need to use them

The size of the Bucket = the Capacitors size, & is measured in Farads
Capacitors are given the unit F

We say we have a 1 Farad Capacitor (1F)
When the bucket- Capacitor holds 1 coulomb of charge with 1Volt measured at the capacitors terminals
Remember 1 coulomb of charge = 6.25 X 10 18 electrons
A Farad is a massive Bucket-Capacitor so we use fractions of a Farad
e.g 100uF = 100 micro Farads 100 x 10-6 Farads
Radio circuits regularly use 2 or 5 pF = 5 x 10 -12 

A Typical Paper Capacitor

Once wound  the Capacitor was dipped in Wax  or Plastic coated

Now for what Our Tester is used for

We’ve all seen lightening travel through the air
When a capacitors plates are close high voltages can spark across the air gap making the Capacitor useless
So Insulators are placed between the Capacitors plates which are called the dielectric

This Leads to the big problem with old Capacitors  

Insulators like Waxed Paper, Mica & wet Electrolytic’s that were excellent 70 years ago degrade
Paper capacitors become conductive and allow Current to flow through them 

While Mica Capacitors suffer from what we call Silver mica disease
The silver coating on the mica breaks down and moves causing electrical leakage

Electrolytic’s dry out or leak their internal electrolyte chemicals over other components

This Capacitor Analyser can not only tell you a Capacitors value 

It can apply up to 500Vdc ( the voltages used back then ) to see if the capacitor is electricly leaking
When a neon lamp will start to flash 

This “ALTHAM” Capacitor Analyser needs a full Restoration
Which I’ll probably go over on my YouTube Chanel when that goes live

Today I use this little Component Tester

 

This can tell me a Transistor or FET characteristics
A resistors Value or a Capacitors Value and its ESR
More on ESR later