Rigol
DSA-815-TG
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My new spectrum analyser
which covers up to 1.5GHz (click picture to see more)
Note the invisible leads... |
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GDS1102U
Oscilloscope
Note again the invisible leads...
Click picture to read its spec.
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AVO
Valve Tester
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Here's my old AVO valve
tester which is virtually indispensable unless one has loads
of valves and plenty of time to swap them around. It was used
by Electronics Lincs in North Thoresby to test TV valves and
it's still got its original handbook.
The handbook is vital as it
provides the settings for the tester. The array of switches and
knobs needs to be carefully adjusted for each valve being tested.
Under the lid is a set of valve bases and the pins on these are
connected to roller switches which are turned to a number 0-9.
These switches set the valve electrodes correctly, after which
the various voltages are set up, the heater or filament, anode,
screen etc. Depending on the type of valve other switches and
knobs are adjusted so that emission and gain can be checked.
Weirdly, the equipment uses
AC not DC to power the valve being tested. |
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RF
Signal Generator TF2008
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This is a Marconi TF2008,
one of the last analogue professional products of this type from
that company. It uses transistors (not valves) of course and
can do most things. One really needs a counter to check exact
frequency output but it has a built-in device to carry out spot
checks if one isn't available. The first counter I had was cheap
and cheerful and had one significant drawback..it leaked RF so
that the superb attenuator ccould't be increased beyond background
level of the leak. To get down to microvolts required the counter
to be unplugged.
The generator has one really
unusual feature. The pointer traverses to the right going from
zero frequency to the top of the first band then, when the next
band is selected, it tunes "backwards" from right to
left, next tunes "forwards" from left to right and
so on in 12 bands to over 500MHz. This gives you essentially
a continuous tuning scale of about 12 feet in length.
I bought it in a "non-working
but easily repairable" condition years ago for a lot of
money. I think mine had been connected to a transceiver which
had inadvertently been put into transmit mode, damaging the output
of the generator. I find it nicer to use than a digital equipment
but a bit fiddly when setting to exact frequencies. This is probably
because I use a digital counter with too many digits. |
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Audio
Signal Generator TF1370
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This was my first audio
signal generator, a Marconi TF1370 which is authentic enough
to use valves but suffers from the drawback of having to warm
up. |
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Tektronix
Oscilloscope Type 454
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I can't abide an oscilloscope
which takes hours to warm up and stabilize so I ditched the various
valved models I had and invested in this Tektronix for which
my bid of £50 was accepted, being surplus to Plessey's
requirements. It's transistors warm up immediately and one can
make measurements within half a minute of switching on.
I no longer use this because
I bought a brand new scope (GDS-1102U)
when the supplier listed them at reduced price for a short period
in September 2013. I paid £276.94 inc VAT and delivery.
Pricing of products such as
this is sometimes very odd. For example, in Dec 2014, Farnell
lists the GDS1102U for £568 whilst sister company CPC has
them at £383. Maplin has them at £419.99, whilst
Amazon lists four at £908.50, £509.99, £761.10
and £481.60. Ebay has them at £438.70, £678.29,
£436.38 and £627.41. A US company has them at $488
which is £312 and in South Africa they are £418.
What on earth is going on. Can
anyone offer an explanation?
The new model has some really
useful features which were undreamed of when Tektronix made the
model 454. I can press a button and immediately see a locked
stable picture of the input just the right size for the screen
and another press I can see the RMS value of a sinusoidal input. |
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Line
Output Transformer Tester
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You can judge when I started this website!
This is my Line Output Transformer Tester.
The key part of all TV sets is the transformer
which develops the high voltage to drive the cathode ray tube.
The LOPT, as it is known, is also pressed into service to provide
subsidiary voltages for many other parts of a TV's circuitry.
Energy that would ordinarily just go to waste as heat is harnessed
to provide things like power for the CRT's heater, voltages to
drive the focus and screen grisd electrodes, and several low
voltage power sources. The LOPT is very highly stressed and a
typical fault is a breakdown within the transformer's windings.
This is usually not an easy fault to diagnose, at least it's
one that could be mistaken for an entirely different fault. The
simple way to find out if a LOPT is faulty is to swap it for
a new one. Unfortunately as there are hundreds of different types
it would be an expensive proposition to carry stocks of all of
them. One of the largest manufacturers of transformers came up
with this little tester which can accurately diagnose most LOPT
faults by emulating the circuitry connected to it in a way that
can determine short circuits between windings, shorted turns
in windings and faulty rectifier diodes in the EHT circuit. Since
I started using it I must have saved many hundreds of pounds
in transformers I never needed to use.
It's now many years since I used this. |
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Variac
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This is a government surplus
variac which is essentially an auto transformer which one connects
across the mains supply to provide an adjustable source of power
for testing faulty TV sets and the like.
I've had this one in the workshop
for ages on loan but recently swapped it with its owner for a
TV repair.
By monitoring input current,
usually across an open fuse holder one can gently increase the
mains voltage and check nothing nasty is afoot.
Be warned though with TV sets
the degaussing posistor presents a low impedance across the imains
input until after a second it gets hot and effectively disappears.
As the control is turned up it is customary to pause while the
posistor gets to operating temperature bedfore looking for meaningful
input current.
This particulatr variac has
plenty of power handling capacity unlike my previous model which
I bought from Maplins which blew up after only a couple of uses.
I've now fitted this device
into a case. |
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Another
Variac
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This is another variac.
It was being chucked out because the owner didn't know what it
was. Inside the home made wooden case, disguised as metal, is
a variac with a horizontal frame rather than the vertical type
above.
This model is wired in a different
way to the one above. It can be adjusted to provide an exact
output voltage over a limited range. |
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Solartron
Power Supply type SRS153.2
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Clearly designed for testing
valve equipment because you can see the output for standard valve
heaters (6.3v). The PSU provides outputs not unlike the Type
234A used for powering the R1132 and R1392 receivers. I recall
looking inside after I bought it and found a series pass circuit
using power valves to provide a variable output voltage.
It uses five valves, a pair of 5B/254M
(CV428) beam tetrodes for output voltage control and three diode
rectifiers, type EY84. As I recently (2019) needed to repair
this equipment I checked the circuit details. The two 5B254M
valves are connected in a series pass circuit with their anodes
supplied by two HT rectifiers in a full-wave swinging choke arrangement
with the HT transformer centre tapped to ground. The third diode
rectifier cathode is fed from the same HT transformer winding
to produce a high voltage negative supply. This is filtered through
a pair of capacitors and a 470Kohm resistor to supply a bias
voltage to the grids of the 5B254Ms. The HT output voltage is
determined by the setting of the slider of a potentiometer wired
across the HT and the bias voltage. All nice and simple and extremely
rugged and straightforward when compared with its modern solid-state
equivalent.
When mine failed, due to connection
across something modern that happened to fail short-circuit,
the excess current through the 5B254Ms resulted in failure of
screen grid resistors. One burnt up and the other went high in
value. These appeared to have once been 47ohm resistors. I fitted
two new resistors plus two new anode "stopper" resistors
which had risen in value from their marked 100 ohms. The 1Kohm
grid resistors were both a bit high at 1.5Kohm but as they're
not critical I left them. There are a couple of cathode resistors
which are high stability 10ohm ceramic bodied components in perfect
condition. The failed anode and screen resistors were very low
wattage and perhaps chosen as such to act as fuses in the event
of an overload?
See
a new power supply I'm building
Here's some pictures of the
inside of the Solartron SRS153.2
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This is the best example of the circuit
diagram I could find, but as the circuitry is so simple you can
easily follow it. |
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It's often useful to have
two independent HT power supplies and I was pleased to receive
this second Solartron (above) from Steve Kaplan. This model looks
slightly newer than my first example, having a different meter.
He also presented me with this oscilloscope. |
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Philips
Frequency Counter type PM6611
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The Philips PM6611 has a single input
connector which accepts up to 80MHz with a sensitivity of a nominal
10mV dropping off at higher frequencies. Input impedance is 1Mohm
and some switchable signal processing which helps it accept either
sine or square wave inputs and improved performance below 100KHz.
In practice this example handles inputs at over 100MHz. |
Racal
Frequency Counter type 1991
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The Racal 1991 has two input sockets,
0-100MHz (Input A) and 0-160MHz (Input B) with sensitivities
of 25mV rising to 50mV towards the upper frequencies. Input impedance
is selectable at 1Mohm or 50 ohms.
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Fluke
Counter type 1953A
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This model of the Fluke 1953A
has three input sockets designed to accept 0-25MHz (Channel A),
0-125MHz (Channel B) and 0-512MHz (Channel C which includes a
prescaler). Generally the sensitivity is 30mV, falling off towards
the maximum frequency ranges. The input impedances are aound
1Mohm rather than typical 50 ohms.
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Datalab
Transient Recorder type DL901
I have no information on this
equipment which I bought in a job lot around 2002.
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Farnell
Audio Signal Generator type FG3
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The FG3 is a very handy
instrument providing extremely low frequency signals up to a
couple of hundred KHz. It'll need an external attenuator if the
variable control is found to be too inaccurate. It also has a
swept output. |
Black
Star LDO100
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I now prefer to use this
Black Star audio generator as its display gives the frquency
and amplitude of the output. For years I put up with a major
failing though. The on-off switch is a rocker switch on the rear
panel and as the instrument is fitted into a space in a rack
it was always awkward to turn it on and off so yeterday (12th
August 2021), I dismantled the thing and drilled the aluminium
front panel for a switch and a red LED. The latter is fed from
the on-board 9 volt supply via a 680 ohm resistor. As you might
be able to see the BNC socket is fitted with a phono adaptor. |
Racal
Frequency Counter type 9915
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The Racal 9915 has a better sensitivity
(down to 10mV) than the earlier 1991model above and has two input
sockets tailored for up to 60MHz (Input B) and 40MHz to 520MHz
(Input A). Note that Input A is rated at 50 ohms whilst Input
B is 1Mohm.
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Wavetech
Signal Generator type 2407
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Hewlett Packard
Power Meter type 431C
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Hewlett
Packard VHF Oscillator type 3200B
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Like some of my receivers, the
R206 and DST100 plus the W2508 Wavemeter, this VHF Oscillator
has a turret tuner carrying coils for its different wavebands.
The Oscillator has a pair of 6DZ4 valves operating as a multi-vibrator.
A design weakness is the rather flimsy knob which not only operates
the turret, but also flips the tuning scale to match the selected
coil. |
Power Unit Type
234A
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This is the AC power supply
for the R1392 and R1132 receivers although it's fine for powering
lots of wartime stuff.
Mine is missing its plug-in
moving iron meter, but works OK without it. Under the light grey
fuse panel lid there's a setting for changing the HT output between
high and low. |
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A
miscellany of small testers I use all the time
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Integrated circuits rarely
fail when left alone, but lightning, power supply problems and
of course electronic enginers or technicians can be a big influence
on them.
This simple tester can evaluate
the type of integrated circuit and check it functions correctly. |
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Peak Testers
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One of the most useful
testers ever invented, this device tells me if a capacitor has
reached end of life. Much like radio valves electrolytic capacitors
have a finite lifetime. This can be dramatically reduced if subjected
to a high ambient temperature or if they're subjected to AC. |
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I mislaid my ESR70 recently
and because I deal with urgent repairs I had to buy a new one.
Pretty expensive, but to my surprise the new example was really
good because it overcomes a few problems met when using the old
one. For example you turn it on, connect the probes and it automatically
detects the capacitor and displays the capacitance plus the ESR.
The latter resistance value is now up to 40 ohms so provides
a much greater range of measurements.
The power is now provided by
a AAA cell instead of the special 12 volt battery which is really
useful.
My XYL's help is no longer required
to press buttons.
A few days later I found the
old one... |
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I use this tester mainly
for checking inductors. |
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This tester tells me if
a triac or thyristor is serviceable. |
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Despite its vague name, this tester
is for transistors including FETs, Darlingtons and insuated gate
types. |
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Not so much used, this tells me the
characteristics of zener diodes. |
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This tester has been superseded by
the component tester above but was very useful when I first acquired
it. |
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Mega328 LCR-T4
Here's a recent purchase. The
tester comes as shown opposite but to protect it and to improve
battery life I use a set of 6 AAA cells instead of a PP3 and
fitted it into a cheap plastic box.
You can use two or three test
leads to test virtually anything. I've included the (un-edited)
spec below. Clearly it would get confused with very small coils
and very small capacitors so for those I use one of my other
testers, but the ESR feature works surprisingly well and gives
more information than the Peak ESR tester (above).
I later added a small on/off
switch to prevent the battery discharging when not in use, and
a bezel to improve its looks. |
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Description:
1,2013 latest M328 version of the software ,more functions.Chip:
Atmega328
2.128*64 big Backlight LCD display,only 2mA when stand by.
3,Using 9V battery (Not included)
Test ranges:
Inductors, capacitors , diodes, dual diode , mos, transistor,
SCR , the regulator, LED tube , ESR,
Resistance,Adjustable potentiometer
Resistance :0.1 ohm resolution, maximum 50M ohm
Capacitor :25pf -100,000 uf
Inductors : 0.01mh-20H
Function:
1:Automatic detection of NPN and PNP transistors, n-channel and
p-channel MOSFET,
diode (including double diode), thyristor, transistor, resistor
and capacitor and other components
2: Automatic test the pin of a component, and display on the
LCD
3:Can detect the transistor, MOSFET protection diode amplification
coefficient
and the base to determine the emitter transistor forward biased
voltage
4: Measure the gate and gate capacitance of the MOSFET threshold
voltage
5:Use 12864 liquid crystal display with green backlight
Specifications: For you reference:
1,One -button operation, automatic shutdown .
2,Only 20nA shutdown current.
3,Automatically detect NPN, PNP bipolar transistors , N -channel
and P -channel MOS FET,
JFET , diodes , two diodes, thyristors small power unidirectional
and bidirectional thyristor.
4,Automatic identification components pin arrangement .
5,Measuring bipolar transistor current amplification factor and
base - emitter threshold voltage.
6,Via the base - emitter threshold voltage and high current amplification
factor to identify Darlington transistors.
7,Can detect bipolar transistors and MOS transistors protection
diodes.
8,Measuring the gate MOS FET threshold voltage and the gate capacitance.
9,Can simultaneously measure two resistors and resistor symbol
is displayed.
Displayed on the right with a decimal value of 4 .
Resistance symbol on both sides shows the pin number.
So you can measure the potentiometer.
If the potentiometer wiper is not transferred to an extreme position
,
we can distinguish the middle and both ends of the pin.
10,Resistance measurement resolution is 0.1 ohms , 50M ohms can
be measured .
11,Can measure capacitanceCan measure capacitance of 30pF-100mF
, resolution 1pF.
12.2uF more capacitors can simultaneously measure the equivalent
series resistance ESR values.
The two can be displayed with a decimal value , resolution 0.01
ohms.
13,Can be in the correct order and the diode symbol display two
diodes , and gives the diode forward voltage.
14.LED is detected as a diode forward voltage higher . Combo
of the LED is identified as two diodes.
15,Eeverse breakdown voltage is less than 4.5V Zener diode can
be identified.
16,Can measure a single diode reverse capacitance.
If the bipolar transistor connected to the base and collector
or emitter of a pin ,
it can measure the collector or emitter junction reverse capacitance
.
18 can be obtained with a single measurement rectifier bridge
connection. |
Alas this device (and its replacement) didn't last
long.. maybe failing due to a residual stored voltage on tested
capacitors? |
GW Instek GDM8145
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I bought this attractive-looking
bench multimeter many years ago, when they'd just been introduced,
to aid fault-finding.
Alas, I only used it a few times
because of a serious problem which I think wasn't a fault but
just bad design. I'll go into this below, but maybe you can guess
by looking at the adjacent sales picture? |
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Having a free moment or
two and noticing my multimeter sitting in the test equipment
rack and having recently seen some U-Tube videos where a bench
meter was being used I decided to renew my acquaintanceship with
my GDM8145.
I pulled it out and found to
my surprise that it uses a stand-by switch, not a mains on/off
switch and for the past umpteen years its transformer had been
powered up. I switched it on and the display was really awful.
Not only was it mostly dim but one of the five 7-segment displays
was glowing a solid red. I recall the dim display and this had
been my chief reason for effectively binning the brand new tester,
but now it seems to be offering an opportunity for fixing it...
Incidentally, in the smaller
picture above you can see the problem where ambient light makes
it tricky to read the display, but now not only is the display
dim but there's a fault as well. These 7-segment displays use
a timing arrangement to display a set of numbers. This is aided
by a 7447 chip which selects and drives the segments in accordance
with data supplied to it with the end result a dimming due to
the multiplexing function. If for any reason the multiplexing
fails one or more displays will be a lot brighter and this was
the fault with which I was confronted.
I opened the case and removed
the main circuit board together with the front panel carrying
the display board. A quick check didn't reveal a problem as everything
looked pristine.... except that I found a 10 ohm resistor on
long legs running exceedingly hot. Voltage checks revealed the
DC voltage circa 8 volts feeding the 5-volt regulator circuit
was running at 250mA, and a quick look on the schematic revealed..
it shouldn't be there.. no resistor had been fitted in the original
design.
Clearly the resistor had been
fitted for a purpose. In fact once the current increases due
to a fault the feed to the 5 volt regulator falls and will kill
the logic circuits and more importantly limits the 7-segment
display current. I unplugged the display board and the current
fell to virtually nothing proving the fault was thankfully on
the display board not on the exceedingly crowded motherboard.
I checked the components on
the display board and noticed a set of PNP/NPN transistors connected
to the display chips. I checked them with my diode-tester and
soon found an anomaly. One of the 2SC1815 NPN transistors had
a base emitter reading suggesting both NPN AND PNP characteristics.
I removed it and fitted a new 2SC1815 and this fixed the fault,
however... is there a way of increasing display brightness?
Each display is essentially
a set of LEDs and these will get brighter the more current is
passed through them. Between the 7447 chip and the displays is
a set of 100 ohm resistors and I quickly discovered that reducing
their value increased display brightness so I removed them and
fitted a set of 10 ohm resistors.
I reassembled the meter and
now the display is comfortably bright with unlit segments no
longer making things awkward. |
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A 15 ohm resistor plugged
into the sockets.
The switchery is a bit confusing
but after a bit of practice I'm sure I'll figure it out... |
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A couple of years later I
switched on the meter to check a suspicious voltage, not believing
my usual test meter and the display flickered a few times and
went out. After a few button presses with random results the
meter filally went dead and stayed that way. I dismantled it
and checked a few things. Mains was present but the pcb was coated
or at least it was difficult to get resistance readings. My first
thought was a bad capacitor but surely not because it had been
switched off and capacitor lifetime should be quite long.. but
then again the on/off switch was in a low voltage lead and merely
turned on a relay.. so at least part of the meter had most likely
been on for donkeys years! I set it on one side for later.
The following week I started by checking the capacitors
(in circuit) and found a couple had strange readings so attempted
to just parallel up some new ones. All to no avail so I made
some voltage measurements. Three seemed OK but no sign of 5 volts
and without the schematic I was mystified. I eventually found
the manual and printed off the circuit diagram (three pages).
The power supply (shown further down) actually uses series pass
transistors and I found a 2SD313 provided the 5 volt rail. This
was governed by a 5.6 volt zener diode but where was it? It turned
out to be adjacent to another power transistor and of course
it was short-circuit.
I fitted a new 5.6 volt zener and the meter worked
fine. In fact I'm pretty sure the thing had been dodgy from the
day I bought it because readings were now rock steady instead
of jumping around. |
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With the circuit diagram (below) I was able
to figure out why the ground voltage wasn't present on what I'd
vaguely imagined was the centre pin of a 3-terminal regulator
(in fact a 2SD313 transistor, Q103). Without decent light and
magnifying goggles the lettering on the components is not easily
readable.. grey on grey.. one of my pet hates. The transistor
pins are base/collector/emitter hence the heatsink (=collector)
is at 12 volts. The base was at ground potential because of the
duff diode (D107). |
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S101 is the on/off switch and as you can see
it doesn't turn off the mains supply, leaving some circuit drain
via losses and leakage.
I have a new-fangled device for measuring mains power
(part of the "green" revolution) which tells me that
the meter consumes 1.6 watts at 234 volts AC when "OFF"
and 6.4 watts when "ON".
Below, the rear of the circuit board which is lightly
treated in some sort of conformal coating making it tricky to
take measurements! |
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