Practically Speaking
Hands-on techniques for turning ideas into projects – by Jake Rothman
Restoring old equipment – Part 1
T
his is the start of a series
about restoring old and vintage
electronic equipment. Before we
proceed it’s worth asking an important
question. Given the throwaway nature
of so much modern electronics, is restoration worth it? Well, that depends on
many factors. If it has historic value, this
can be sufficient to justify a restoration
well beyond an economic repair. Organisations, such as The National Museum
of Computing at Bletchley Park and the
Museum of Science and Industry in Manchester, rely on vintage-electronics experts,
because preservation is at the core of their
work (and also, working exhibits attract
more visitors!). I remember blagging free
entrance for myself and a few teenagers to
Bletchley Park by offering a bag of Mullard OC42 transistors to help restore an
old computer.
Sometimes, restoring electronic
equipment is part of a larger restoration
program. Enthusiasts have painstakingly
replicated 1960s electronic control cards
for an English Electric diesel locomotive
(Fig.1). Heritage railways and curators
of cold-war-era V-bombers have to have
their old-world electronics operational.
The driving force to restore is often
deeply nostalgic and personal. All
engineers have formative childhood
experiences that set them on the path to
designing their own equipment. It was
gazing down at the electronic ‘city’ of
glowing valves through the ventilation
slots of 1960s TVs that set me off on a
lifetime of electronics, aged six. Also,
Grandad’s polished wooden radiogram
with a Roger’s valve amplifier and
Wharfedale loudspeaker emanating the
strings of Albinoni’s Adagio kicked off
the Hi-Fi bug in me. Upon inheriting his
pride and joy as a teenager, I promptly
pulled it all apart to see how it worked!
Some items are iconic British brands;
for example, Quad, Leak and Vox guitar
amplifiers, for which there will always
be a demand. Before globalisation,
many countries had their own national
electronic brands, fostering a sense of
tradition and place, further feeding
Fig.1. Who’s going to keep the early 1960s
electronics going in these old locos? (They
produce excellent sound for sampling!)
Fig.3. A restorer friend’s workshop; note the stack of aerosols and minimal test gear.
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Fig.2. A selection of old Roberts transistor radios – we’ll be doing them up soon.
nostalgia. In Denmark, it’s B&O, in the
Netherlands it’s Philips and in Japan
it’s Sony. I could go on, but what British
readers of a certain age cannot identify
with a happy childhood memory of a
Robert’s or Bush playing radio in the
kitchen? (see Fig.2). Just the mention
of a Mullard EL84 audio output valve
or a germanium OC71 transistor brings
it all back.
Whatever your motivation for restoration
there is no doubt that it is a great way
to learn hands-on electronics and
troubleshooting. I certainly picked up
a huge amount of knowledge about how
to build and design equipment, plus a lot
of insight into how not to build things!
Practical Electronics | November | 2020
Fig.5. Old paper capacitors often leak
electrically. I find anything made by Hunts
seems to be particularly unreliable.
Fig.4. Old components usually fail visually.
This smoothing capacitor’s safety vent
has clearly blown.
Restoration work is essentially practical,
an electronics degree is not required and
is possibly even a hindrance. I know many
people who effectively restore equipment,
knowing very little electronic theory and
not even using circuit diagrams. This
is achievable because many faults on
old technology can be found simply by
visual inspection (see Fig.4) and good
old ‘swapnostics’ – find a broken part
and just swap it out. No fiddly software
updates needed for old gear.
paper dielectric capacitors (Fig.5) go
low resistance. When restoring a piece
of equipment over 30 years old, expect
to remove a large pile of such parts. The
pile of failed parts shown in Fig.6 was
from a Leak Stereo 30. A typical resistor
problem is shown in Fig.7.
New LEDs for old lamps
Fig.6. A pile of faulty components
taken out of a 56-year-old Leak stereo
30 amplifier. Surprisingly, the output
transistors were fine.
Selector is the best book for optimising
transistor substitutions. There are PDFs
online available from the Internet Archive
and Google docs.
NOS – ‘New Old Stock’
One of the biggest challenges facing
would-be restorers is sourcing parts.
Entropic ageing processes, damp ingress,
heat, dust, oxidation and leakage
reduces many electronic components
to scrap in old equipment. Plenty of
past components, such as resistors,
transistors and capacitors are simply
inferior to modern designs. Carboncomposition resistors drift high with
age, germanium transistors had relatively
bad die processing and contacts. Poorly
sealed electrolytic capacitors dry-up and
The problem of parts leads to one of
the biggest quandaries for a budding
restorer. There are two approaches to
take; restore using ‘original’, possibly
poor-quality parts, or use new ones, that
will look completely wrong. Here one
may start redesigning the unit, which is a
mistake many educated engineers make.
I regret doing this myself to Quad II valve
amplifiers. First, it destroys history; and
second, the effort is better channelled
into a completely new design. If the
radio dial was illuminated with warm
incandescent light bulbs, don’t ‘upgrade’
it with blue LEDs. True enthusiasts have
been known to stuff new plastic-film
capacitors into the cases of old paper
capacitors where the correct replacement
is unobtainable. If you do ‘improvements’
make sure they are reversible. If you have
to substitute transistors, keep the old
blown ones for historical completeness
– a museum or collector may thank you
for it. Tower’s International Transistor
Watch out when buying ‘vintage’ or
new-old-stock components. If they
have been stored for 50 years then there
will be a fail rate of at least 10%. The
moral, buy more than you need for the
repair. I found an unopened box of 200
germanium diodes dated 1963 (see Fig.8).
Upon cutting the animal glue paper-tape
seal I could smell the coal smoke from
the steam goods train they probably
travelled on, a pure olfactory nostalgia
trip. A particular problem with NOS
germanium transistors is ‘re-marks’.
This is because manufacturers in the
1960s and 70s sold their rejects on the
open market to companies like Bi-Pak
Semiconductors and Bi-Pre-Pak Ltd
(Fig.9) They were usually just unmarked
metal cans, until some enterprising
people bought labelling machines and
sold the devices on. However, the game
is usually given away by the large font
size and lack of manufactures markings
and date codes, as illustrated in Fig.10.
I have found re-marks to be especially
Fig.7. Carbon composition resistors
are prone to go high in value with
time, especially values above around
10kΩ. These Erie ‘pluggable’ types are
especially prone. This one has gone from
its stated value of 470kΩ 5% to 600kΩ.
Fig.8. A box of CG92 germanium diodes
from 1963. When opened I could smell
the sooty sixties. I bought these from
John Birkett’s electronics shop in Lincoln
in 2010. He’s still trading and has still got
some in stock.
Fig.9. A Bi-Pak Semiconductors ad from
the September 1968 issue of PE. These
dodgy devices are still circulating on eBay
and cost around £3 each, rather than
the original 10/- (50p) for a pack of 60
germanium transistors.
Component issues
Practical Electronics | November | 2020
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Fig.10. A remarked (top) versus genuine
(below) ACY17 high-voltage germanium
transistor. Test the remarked device
thoroughly for leakage, Hfe, max Vcb and
noise before using.
common on eBay and at radio rallies.
Often the vendor is genuinely unaware
there is a problem.
Digital test gear
The most important thing to have is a
DMM/multimeter to measure voltages,
current and resistances. An oscilloscope
is pretty essential for setting up power
amplifiers properly. (Although many
audio restorers do a successful job by ear.)
If you really want to get moving, digital
innovation has come to our rescue. I
remember back in the early 1990s I met
Jeremy Siddons of Peak at the Buxton
Audio Constructor’s Show. He had his
design for a transistor tester that gave the
pin-outs and test data for any transistor
connected to it. I stuck
it on some old OC22
power transistors and
it identified them as
germanium and most
importantly gave the
leakage current and a
true Hfe reading. I said
he would do brilliantly
with that design, and he
did. Nowadays, we all
now know his company
as ‘Peak Electronic
Design’, and I reckon
his semiconductor
and electrolytic ESR
testers have saved more
electronic equipment
from going to landfill
than any environmental
initiative. One only
has to observe all the
YouTube presenters,
such as Radiocruncher,
who use them regularly
(see: http://bit.ly/penov20-crunch). Fig.11
and Fig.12 show my
Peak testers being used.
The Internet has of
course revolutionised
renovation and repair.
It’s become highly
effective for sourcing
advice, photos and
circuit diagrams.
Fig.11. The Peak transistor tester is a godsend for all
repairers. What use is a transistor with an Hfe of 2?
Fig.12. The Peak ESR tester is great for detecting dried-out
electrolytic capacitors. It can test capacitors that are still soldered
into the circuit. No need to push buttons; it resets as you move
from one capacitor to another. A cost-effective device for all
restorers. Here the capacitor will work fine, despite drifting high.
Old can be better
Sometimes a restored audio product is
preferable to a new one. For example,
old Roberts FM radios have cases made
out of wood, giving a much better sound
quality than a modern plastic minimal
bit-rate DAB equivalent. I’d draw the line
though at watching a 4K Netflix movie
on a 405-line 1964 black and white Bush
TV! However, should you wish to, there
are HDMI-to-405-line converter interfaces
available. The National Science and
Media Museum in Bradford may have
commissioned some from British Vintage
Wireless Society members.
Their magazine has some of the most
beautiful restorations I’ve ever seen.
There is also the fact that the old stuff
that has survived has been built to last
and be repaired, something that has got
lost in today’s world of disposable tat.
(See: http://bit.ly/pe-nov20-bvws).
The boring bit, cleaning and health
& safety
Fig.13. Leak Stereo 30 front panel: take the knobs off and remove for ease of cleaning.
The great thing about old gear is that it
was designed to be built by hand, not
automated processes, so it is easy to
disassemble. However, this leads to the
worst bit of restoration – cleaning! We all
want to get straight to the electronics, but
the dirt on old tech can be horrendous
and has to be removed first. It also looks
horrible, no one wants to see an old
radio that’s been on a shelf above a
cooker for 30 years. Although I suppose
you could get a Martin-Parr-style photo
out of it first.
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Practical Electronics | November | 2020
Fig.15. Roberts radio cleaned of dust –
those pulleys are less likely to stick now.
Fig.14. When disassembling, take the opportunity to clean normally inaccessible areas,
such as the tuning drive under the panel of a Robert’s R600 radio. A multi-tufted dusting
brush is a vital tool.
The first rule of cleaning front panels
is always remove the knobs, as shown in
Figs 13. Fig.14. shows the muck found
under a tuning dial on a Robert’s radio. To
prize off push-on knobs I use a rounded
table knife to get under the edge and
gently lever up. WD40 can help with
seized-on knobs and to make it easier
next time I appy a little silicone grease
(which never dries up) on the shafts.
I once bought some old BBC mixer
modules from under the railway arches at
M & B Radio in Leeds. Huffing and puffing
I blew off loads of white powder from the
innards only to find that they had come
from an asbestos-filled attic in Armley
near Turner & Newall’s infamous factory.
I hate to think how much rosin, lead,
cadmium, PVC monomer and beryllium
dust I’ve inhaled restoring old gear. I often
hear the most horrendous cancers being
discussed at radio rallies among ‘senior’
restorers. Acute myeloid leukaemia is
significantly higher among people who
work in the electronics industry. So do
be careful: read labels, wear masks and
wash your hands – you have been warned!
Once the toxic dust is off (Fig.15) it’s
time to get the organic solvents out,
not carcinogenic ones! My favourite
is good old IPA, not the beer, but isopropyl alchohol or propan-2-ol to give
it its correct name, as shown in Fig.16.
It is most effective for tackling old rosin
flux residues. Luckily, this replaces the
poisonous carbon tetrachloride trichloro ethane, benzene and other horror
substances that would have graced any
workshop in the 1970s.
For Perspex front panels (Fig.17)
and the like it is fine to use washingup liquid and water, though not a good
idea to use near the electronics. Another
favourite is label remover, especially the
citrus-oil based type for removing sticky
organic materials that IPA won’t dissolve.
Take care you don’t remove component
markings with solvents.
D anis h oil is
great for buffing up
the teak wooden
ends that grace so
Fig.16. Cleaning solvents for non-electrical parts: degreaser/
label remover, IPA and WD40. Also use water and washing-up
liquid. We’ll cover electrical contact cleaning next month.
Practical Electronics | November | 2020
Fig.18. I just love teak end-panels on
old 1970s consumer electronics. I’ve
noticed Hammond Manufacturing have
reintroduced these on a new range of
cases. Rub in Danish oil, allowing six
hours between coats to restore.
many 60s and 70s products, as shown in
Fig.18. For the final hit, a Novus scratch
removal kit, as used by motorcyclists for
their polycarbonate visors, with its three
grades of abrasive liquids is most effective
for plastic panels such as meter bezels
(https://amzn.to/33MQKWP).
That’s enough scrubbing, screwing
and sniffing. Next month, I’ll get down
to some real electronics as we start to
restore a Leak Stereo 30; Britain’s first
successful Hi-Fi transistor amplifier,
introduced in 1963.
Fig.17. The cleaned Perspex front panel of a Robert’s radio. Fill
in the scratches in the back printing with black gloss modellers
paint. Minor scratches can be removed with very gentle
abrasives such as Novus scratch remover. The silver edging
strips and knobs were all cleaned separately.
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