This is only a preview of the May 2021 issue of Silicon Chip. You can view 0 of the 112 pages in the full issue. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "Programmable Hybrid Lab Supply with WiFi – Part 1":
Items relevant to "Digital FX (Effects) Pedal – Part 2":
Items relevant to "Arduino-based MIDI Soundboard – Part 2":
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Grateful for donated test equipment
A few months ago, I sent you an
e-mail about a BWD instrument I wanted to repair, and expressed interest in
buying other BWD products.
Thank you for publishing this for
me. I have been given two oscilloscopes by your readers, for which I
am very grateful.
When I am too old, I plan to give
my collection to Wireless Hill Museum here in Perth. So thank you for all
you have done for me.
Trevor Collins,
Bellevue, WA.
Giving away console radios & chassis
As a keen reader of your fine publication, I have been engaged in electronics for the last 60 years. I have repaired and restored many valve sets
and military equipment. As a result,
a lot of ‘to do’ items have heaped up.
With advancing age and deteriorating eyesight, things have come to
a halt. Having lost colour perception
and fearing high voltages, I have decided to call it quits.
I have about two cubic metres of
console radios and chassis. This includes a Tasma, a Stromberg-Carlson,
an unusual Sanyo, Radiola and other
chassis for fixing or pillaging.
I would like the whole lot to go to
a keen restorer. Should any of your
readers be interested, contact me by
e-mail to discuss details. Most of this
gear is untouched.
W. Schaaij,
Broken Hill, NSW.
pimschaaij<at>gmail.com
in the April issue identifying the Test
Master was good feedback.
I am prompted to see if your readers can identify another piece of test
equipment. I was given a Transistor
Test Set (see photo below) which has
no identification as to its source. It also
has laced cabling, so it might also be
a Telecom training exercise.
Does the name ACE on the meter
face have any significance? Probably
not. The test set has a professionally-made front panel, but the squarecased meter seems to be a substitute
for what could have been a circular-cased original. Also, the ADJ.Vgs
knob appears to be from an AWA radio, not original.
In David’s article, he also mentions
that 10% of NOS (new old stock)
KT88s are gassy. There is a trick worth
trying with KT88s (and KT66s) that
test gassy; let them run for 24 hours
with only 6.3V heater voltage applied.
This can sometimes restore them to a
usable state.
Many years ago, I designed test amplifiers using KT66s for AWA’s loudspeaker factory test rooms. After the
annual factory Christmas holiday
shutdown, when switched on for the
first morning, the fuses would blow;
gassy valves! I eliminated this by running the amplifiers with the rectifier
valve removed the day before the factory resumed production in subsequent years.
That warmed the valves without HT
applied and drove out the gas, solving
the problem. Mind you, that was only
after a few weeks, not many years.
Also in the March issue, in your “All
About Capacitors” article (page 75), I
believe I have spotted the first use in
Silicon Chip of the correct SI prefix
for high-value electrolytic capacitors;
68mF, not 68,000µF!
Why do all manufacturers persist
with non-SI designations? I still remember the days when a 1nF capacitor was designated either 1,000pF,
1,000µµF or .001µF. At least they have
got that right!
Ross Stell,
Kogarah, NSW.
Comment: many hoarders refuse to
admit as much; kudos to you for doing so! The main reason we do not use
Letter from an admitted hoarder
Dr David Maddison’s article, “Hoarding: Urban Electronic Archaeology”
was very interesting (March 2021;
siliconchip.com.au/Article/14773).
It appealed to me because I too am a
hoarder. The response from two former Telecom apprentices in Mailbag
4
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
GME Australia
mF very often is that many people incorrectly use mF when they mean µF,
leading to confusion; possibly this is
because they do not know how to generate a µ symbol.
GME (www.gme.net.au) is a privately
owned company that designs, develops,
manufactures and distributes worldclass radio communication equipment
right here in Australia.
We are proud to be Australia’s only
manufacturer of UHF CB radios, with
our state-of-the-art engineering and
manufacturing facility in Western
Sydney.
Geekcreit LCR-T4 and
germanium transistors
Hiring Senior RF and
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And we are Hiring!
We are always on the lookout for Senior
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6
Silicon Chip
I have a version of the LCR-T4 Mini
Digital Multi Tester that you reviewed
(February 2021; siliconchip.com.au/
Article/14755) and, as you say, it tests
many devices quite well. While not a
problem for most people, my unit fails
with germanium transistors, though.
James Greig,
Spring Gully, Vic.
Comment: you are right; it does not
handle germanium devices well. That
is likely because their base-emitter
conduction voltages are considerably
lower than silicon types, and below
its detection or operating threshold.
Capacitors article was informative
I’m just writing a short note to say
how much I appreciated the piece by
Nicholas Vinen titled “All About Capacitors” (March 2021; siliconchip.
com.au/Article/14786).
With no formal training in electronics, I have always fallen back on my
high school physics description of two
metal plates separated by an insulator.
I don’t think I will even look at another capacitor the same again. From now
on, I shall ask myself “what would
Nicholas say about that capacitor in
that application?”
Keep turning out the great magazine. I don’t build too many of the
circuits anymore but enjoy reading
about them and the other various articles each month.
Cliff King,
Oxley, Qld.
Tantalum capacitors prone to failure
Thanks for the informative article
on capacitors in the March 2021 issue
(siliconchip.com.au/Article/14786). I
have a few comments regarding tantalum electrolytic types.
I had a recent failure (smokey explosion) inside a piece of commercial
test equipment which involved 10μF
16V miniature bead-type tantalum
capacitors.
I had never had a problem with
these before, and assumed them to
be safe and reliable. But then I ran a
web search for “tantalum capacitor
failures”.
Australia’s electronics magazine
It appears that these devices can
have a catastrophic thermal runaway
condition leading to destruction and
damage to nearby components if there
is sufficient power supply energy.
Otherwise, they fail short-circuit.
This often occurs a short time after
the equipment is turned on.
The consensus for use appears to be
that they should never be allowed to
receive even a momentary reverse polarity voltage; should not be connected
directly across a low impedance/high
current voltage rails; should always
have some series resistance to limit
current flow in the event of failure;
be operated at no more than 50-60%
of their rated voltage; and must not be
overheated when soldering.
In my case, one capacitor was across
the 15V supply and self-destructed
with noise, light and smoke. The second capacitor was connected as a transistor collector bypass and fed from
the 15V rail via a 10W resistor – it had
gone short-circuit and toasted the 10W
resistor.
Ashley Smith,
Flagstaff Hill, SA.
Comment: We have also found that
older style tantalum capacitors are not
reliable long-term. Modern types are
used extensively in computer equipment and do not appear to be a significant source of failures, although that
might change as they age.
If your list of restrictions were accurate, that would make tantalum
capacitors pretty much useless. The
main reason to use them is their low
ESR value; hence, they are suitable for
high-frequency bulk bypassing, where
regular electrolytics are not.
We normally use multi-layer ceramic capacitors instead, as they are
superior in virtually every way. Only
in a few specific cases are tantalum
capacitors worthwhile, and in those
cases, you usually need to use the expensive solid types to make using them
worthwhile.
March issue enjoyed
S ilicon C hip March 2021 is a
‘bumper issue’! Super! Regarding the
History of Videotape (siliconchip.com.
au/Series/359), I learned my TV Studio
engineering in Germany, with an RCA
TRT-1, full of valves. “Statistically, one
is dead all the time”, commented our
instructor. I even mastered the art of
editing (physically cutting) tapes by
hand; it often worked.
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Silicon Chip
More details wanted on digital radio modes
Thanks for the article on Digital Radio Modes in the
April 2021 issue (siliconchip.com.au/Series/360). By the
way, the correct spelling is Hellschreiber, not Hellshrieber.
Despite that mistake, I found the article interesting.
Perhaps you could also expand on HF radio data modes
such as PACTOR and the more recent VARA (which
works amazingly well with a PC soundcard). These
modes offer quite high data rates on voice bandwidth
radio channels.
Horst Leykam,
Dee Why, NSW.
Comment: as you will see in part two this month, we mention PACTOR but not VARA. There are so many different
encoding schemes that it is difficult to cover them all.
Multi-amplifier module wanted
Prices are subjected to change without notice.
8
Then the Bosch-Fernseh Quadruplex came along. It
looked like a rebadged Ampex VR-1000A. The article
explains things so well; I wish I had it 50 years ago! I’m
looking forward to the follow-up parts.
Then the Urban Electronic Archeology article by Dr
David Maddison (siliconchip.com.au/Article/14773) reminds me of my outback electronic garage...
And last but not least, Nicholas’ article about capacitors (all about – really!). That article must have taken
years of research; a masterpiece (siliconchip.com.au/
Article/14786).
I have several Sony shortwave radios, very nice ones
at the time, but most of them died because of capacitor
demise. The story goes that these radios (made in Japan)
were made with capacitors from a container full of secondclass devices.
It’s challenging to find the culprits, as desoldering
the suspect caps is required. Strangely, other Sony gear
(amplifiers, Betamax VCRs etc) didn’t suffer, only the
radios – pity!
My local radio repair shop refuses to repair those radios,
but gave me an interesting hint. There is test gear (in kit
form) that allows capacitors to be measured in-situ, without desoldering. How is that possible? Anyway, thanks for
the great magazine.
Hans Schaefer,
Armidale, NSW.
Comment: we’re glad you enjoyed that issue. The Videotape Recording series consists of four parts in total.
Yes, in-circuit capacitor testers exist. They can be affected to some extent by other components in the circuit,
but usually will give you good enough results to know if a
capacitor has failed or not. We have reviewed some in the
past, eg, the EDS-88A in our May 2013 issue (siliconchip.
com.au/Article/3782). We aren’t sure if that device is still
available, though.
As for faulty capacitors, your story reminds us of the “capacitor plague”, which greatly affected computer motherboards and related gear in the early 2000s. We had an
article on the subject in the May 2003 issue (siliconchip.
com.au/Article/6644), or you can read more about it at
https://w.wiki/39AD
I sent you a question recently about the possibility of
installing your SC200 amplifier modules (January & February 2017; siliconchip.com.au/Series/308) in place of
Australia’s electronics magazine
siliconchip.com.au
the ETI series 5000 modules that blew up in my old amp.
I’ve since been pondering changing my system over to
an active crossover type, and was looking at your active
crossover design from 2003.
But building six separate power amplifier modules
is a bit daunting, so I started looking around for a three
amplifier mono module designed for active crossovers.
I haven’t been able to find anything suitable.
What I would like is a quality (stereo) amplifier like the
SC200 for bass, a 50W or so for mid-range and perhaps
a 20W amplifier for the tweeters, all on one board with a
sub-board having the active crossover.
The options that a multi amplifier/crossover like this
would give to the DIY speaker builders worldwide would
be enormous as the ‘black art’ of crossover design is eliminated.
I know this can all be done with modules, but I’m not
sure whether the lower power amp modules are of the
same quality as the SC200, and I’m also not sure whether many would know how to lay out all the modules to
minimise noise etc.
Tony Brazzale,
Bumberrah, Vic.
Comments: low-power amplifiers aren’t much simpler
to design or build than high-power amplifiers as they
still need pretty much all the same ‘front end’ components. You could build SC200 modules but leave one
pair of output devices off (and some of the associated
components like the emitter resistors) to save a bit of
time and money.
Also, keep in mind that if you are building a system
with a mix of low-power and high-power amplifier modules, you will probably need several different supply rails
to achieve good efficiency. For example, ±57V or so for
the 200W modules, and maybe around ±35V for lower
power (50W) modules. That complicates the power supply and wiring.
Another reason you wouldn’t want to run the low-power modules from the higher voltage rails is safety. If a lowimpedance load is connected (like a 4W speaker, or one with
severe dips in its impedance curve), the current is no longer
being spread between multiple output devices, leading to
an increased chance of failure. Running those amps from
lower voltage rails reduces the maximum current drawn.
Another electricity saver scam
I have just seen this advertisement for a “power saving”
device called the Voltex. It is unbelievable. It’s even worse
than electronic rust prevention. See https://getvoltex.com/
article4/au
Bruce Pierson,
Dundathu, Qld.
Comment: it’s frustrating that this sort of scam is still
around (see our previous debunkings of these devices, eg,
in the November 2007 issue). There are only three ways
to reduce what you pay for electricity: get a better rate,
reduce your usage, or steal electricity.
It is possible to reduce your usage by increasing efficiency (eg, getting a better-sealed fridge), but a box that
plugs into the wall isn’t going to do that. They claim a
95% reduction in your electricity bill is possible, making
the stealing electricity option the only viable answer as
to how they achieve it...
SC
10
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
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