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Vintage Radio
By Rodney Champness, VK3UG
Philips 196A 4 -Valve AC/
Battery Portable Receiver
of the time. It measures 280mm long
x 180mm high x 115mm deep and
weighs around 3kg without batteries.
Note that the case isn’t a perfect rectangle, so these are the greatest dimensions in any direction. And although
similar in style, the later Philips 199
transistor model used a case that was
slightly smaller and had pushbutton
controls along the top.
The 196A valve portable has just
three controls: a partly-recessed volume control at top left, a hand-span
dial on the front panel and a small
lever located under the lefthand end of
the carrying strap. This lever controls
a 3-position switch which switches
the set on or off and selects between
battery and AC operation.
This power switch isn’t easy to see
and appears to be something of an
“add-on”. Philips certainly could have
done a much better job when it came
to positioning this control.
Circuit details
Designated the 196A, this interesting little
portable radio from Philips uses valves
and can be run from either batteries or
mains power. It was designed as a lowcost set but is still quite a good performer.
T
HE PHILIPS 196A was produced
during the late 1950s and early
1960s, a time when many manufacturers were already designing and building transistor portables. However,
many customers were reluctant to buy
the transistor radios of the era, as their
performance at that early stage was far
from inspiring.
To overcome this reluctance, some
manufacturers built both valve and
transistor receivers in nearly identical cases. This allowed customers to
choose the type of set that best suited
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their needs and also gave them time
to adjust to the changeover to fullytransistorised sets.
The 196A was one such set. It’s a
relatively small, portable valve receiver and was manufactured right at
the end of the valve era.
As can be seen from the photos,
the case is a little unusual. According to the supplied information (on
the inside of the set), it’s made from
sandstone-coloured, rippled leatherette over stiff cardboard sheets, a
style that was used for many portables
The 196A’s circuit is quite conventional. The front-end employs a
loop-stick ferrite rod antenna and this
forms a tuned circuit with one gang of
the tuning capacitor. The signal is then
coupled to the grid of a 1R5 pentagrid
converter valve.
The local oscillator, which is also
part of the 1R5, operates 455kHz higher than the signal frequency. The two
signals are then mixed together and
the resulting 455kHz signal fed via a
double-tuned intermediate frequency
(IF) transformer to a 1T4 IF amplifier
pentode (the other signals from the
mixer are rejected). From there, the
amplified signal is fed via another
double-tuned IF transformer to the
detector/AGC diode in a 1S5 valve.
The recovered audio at the detector
is then fed via the volume control to
the pentode section of the 1S5 and
following that to a 3V4 audio output
stage. A speaker transformer in the
plate circuit of the 3V4 couples the
audio from the high-impedance plate
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circuit to the low-impedance (3.5Ω)
100mm (4-inch) loudspeaker.
In addition, the receiver employs a
simple AGC system. The AGC voltage
is derived from the only diode in the
1S5 and this is applied to the 1R5 in
the front end. No AGC is applied to
the 1T4 IF amplifier.
Because this receiver works on
both battery and AC power, the valve
filaments are wired in series. The
current drain through them is up to
50mA at 6.5-7.5V on either batteries
or AC mains.
The mains transformer has two
windings: a tapped mains input and
a secondary producing around 130V.
A selenium half-wave rectifier is used
to produce an HT voltage of nominally
90V at 10-13mA to the valve plates
and 7.5V for the filaments via dropping resistors. This may not be very
efficient but it ensures good filtering
of the filament voltage (efficiently
filtered low-voltage power supplies
didn’t become available until transistors became common).
The batteries are relatively small (to
fit inside the case), so a life of around
100 hours would be expected. It uses
a 490P 90V battery for the HT and a
717 battery that supplies 7.5V.
Cleaning & repairing the case
A comprehensive set of instructions on removing the chassis from
the cabinet is pasted inside the rear
cover (see photo). In fact, it’s one of
the most comprehensive I have seen,
so full marks to Philips for this.
The set featured here had obviously
had a hard life up until the time it was
pensioned off. Some of the trim on the
case had come loose and there were
(and still are) several paint marks on
it as well. It was also quite grimy on
the outside.
Having removed the chassis, I removed the plastic grille from inside
the escutcheon, by levering it away
from the case with a broad-bladed
screwdriver (it had been attached
with contact adhesive). That done, I
set about giving it a thorough clean.
I usually place plastic and Bakelite
cabinets in a laundry tub with warm
soapy water and scrub them clean with
a nail brush. However, that’s not possible with a thick cardboard-lined case,
as water will damage the cardboard.
Instead, I simply dampen the outside of the case with soapy water and
then scrub it clean. With continued
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This is the view inside the set without the bottom chassis cover in place. The
label attached to the rear cover details the chassis removal procedure. It
also shows the valve locations, the alignment points and the battery details.
scrubbing, the cabinets usually come
up looking quite good, just as it did
in this case. The plastic grille and
the volume control knob were then
cleaned by immersing them in soapy
water and scrubbing them with a nail
brush. These parts, along with the case,
were then placed in the sun to dry.
Once the cabinet had dried, I tried
lightly scrubbing the paint splashes
with some acetone and while that
helped remove some of the paint, I
also managed to go through the original paintwork in one or two places.
It’s no big deal and I will try touching up these areas with paint when I
have time.
Having cleaned the cabinet, I
realigned the trims around the plastic
grill, filled the gaps with contact adhesive and clamped the trims in place.
This took quite some time, as I had to
allow the adhesive to set in each spot
where it was applied, before moving
onto the next piece.
Finally, the two covers that go over
the ends of the handle were quite dull
and grimy. I rubbed automotive cut
and polish on them and used a small
screwdriver to push the polishing
cloth into the grooves in the covers to
achieve an excellent result.
Overhauling the electronics
The inside of the set was quite clean
apart from some loose dust on various
components. Unlike many other sets
of this era, there was no sign of any
rust or other corrosion.
As a result, a quick dust-out with a
12mm paint brush was all that was required to clean the circuit components
and the chassis.
Having got rid of the dust, it was
April 2012 83
VR1 2k
3V4
1R5
1S5
1T4
+7.5V
7
400 F
10V
T1
230V
AC
D1*
1N4004
A
130V
AC
K
R1*
135
5
1
270
390
7
1
7
1
7
1
40 F
+109V
1 .6k
50 F
150V
* 1N4004 DIODE & 135 RESISTOR FITTED
IN PLACE OF SELENIUM RECTIFIER BLOCK
+90V HT
40 F
150V
NOTE: CIRCUIT DOES NOT SHOW
AC/BATTERY SWITCHING OR
FILAMENT RF BYPASS CAPACITORS
Fig.1: a simplified circuit of the power supply, showing how the 90V HT
rail and the filament supply rail are derived. The original selenium block
rectifier has been replaced by a 1N4004 silicon diode and a 135Ω resistor.
now time to overhaul the electronics. I began by using a high-voltage
insulation tester to check for leakage
between the primary of the mains
transformer and both the chassis and
the secondary winding. There was
no discernible leakage, even with the
tester set to 1000V.
That done, I checked the continuity
of all the battery valve filaments using
a DMM and found that they were all
intact. These filaments are quite delicate so care is needed to ensure that the
correct filament voltages are applied.
As stated above, this set uses a halfwave selenium rectifier block and this
is bolted to the chassis. They are not
very efficient and do get quite hot. In
addition, their impedance tends to go
high, which lowers the loaded output
voltage considerably.
As a result, I applied mains power
to the set and checked to see whether
The selenium rectifier is shown
here at left, together with the diode
that replaced it.
84 Silicon Chip
the output voltages from the power
supply were indeed around 7.5V and
90V. This showed that the filament
voltage was around 3.5V, while the
high tension (HT) was just 65V. These
readings were both much too low and
from experience, it pointed to the selenium rectifier being faulty.
I decided to leave the existing
rectifier block in place and connect a
1N4004 diode in series with a 3.3kΩ
resistor across it. This gave slightly
higher voltages out of the power supply but they were still too low so I
progressively reduced the 3.3kΩ resistor in series with the diode until I got
the correct voltages.
Unfortunately, while I was wiring
these parts in place, one of the lugs
broke away from the selenium rectifier block. As a result, it was removed
and a small tagstrip fitted in its place,
with the diode and resistor wired to it.
The series resistor value came down to
135Ω before I got the correct voltages
for the filaments and plate supplies (ie,
7.5V and 90V). In practice, this 135Ω
resistor was made up of using a 180Ω
5W wirewound resistor and a parallel
470Ω 1W carbon resistor.
Fitting a 135Ω resistor in series with
the diode means that the circuit more
closely mimics the characteristics of
a selenium rectifier.
Keep in mind that a 1N4004 diode
has a peak inverse voltage (PIV) rating
of 400V volts. With a 130V secondary
transformer voltage, the peak voltage
applied to the 1N4004 is around 130
x 2.8 = 364V. I usually take the transformer voltage and multiply it by three
to give me the PIV plus a small margin
for spikes on the power supply line but
if in doubt, always use a diode with a
higher PIV rating.
Because the voltages are not that
high in battery sets, I decided to run
the set for a short time to see whether I
could get it to operate before replacing
any leaky paper capacitors. There was
no output but touching the volume
control produced a “blurt” from the
speaker. I then wriggled the valves in
their sockets and this produced some
loud crackles.
As a result, I switched the set off,
removed the valves and sprayed each
socket with Inox (a spray lubricant,
cleaner). I then reinserted the valves,
slightly rocking them from side-to-side
as I did so to clean any corrosion off
the pins. With power reapplied, the
set then worked but the audio output
sounded quite unpleasant.
At that stage, I quickly switched the
set off again. It was important to keep
this test short, to ensure that no damage to the valves occurred.
Having proved that it worked (in a
fashion), it was now time to replace
any leaky paper capacitors that might
affect the set’s operation. In the end, I
replaced all these capacitors except for
a 100nF low-tension RF bypass and a
4.7nF top-cut filter on the plate of the
3V4. The capacitors that were removed
had between 1.5MΩ and 7MΩ of leakage resistance, so it was no wonder that
the audio was distorted.
This receiver is generally quite good
to work on but sometimes you have to
dig down through up to three layers
of components to get at the parts. As
a result, it can take quite some time to
replace or test some components – not
that you have to do that often.
Mains power lead
The mains power lead is a 2-wire
(figure-8) type with a moulded 2-pin
mains plug and a 2-pin socket that
plugs into the side of the receiver. It
isn’t practical to replace the lead with a
3-core lead and the set is largely double
insulated anyway. In fact, if the power
switch had a plastic recessed type
knob, it would probably comply with
the latest electrical safety standards.
In the meantime, the set can be used
with a 1:1 (230V-to-230V) isolation
transformer.
Unlike this set, some sets of the era
were designed to run from both AC
and DC mains supplies (ie, 200-250V
AC/DC) and so didn’t use a power
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transformer. These particular sets
were “hot chassis” (ie, the chassis and
various components operated at mains
voltages) so extreme care was needed
in servicing them, otherwise electrocution was a distinct possibility.
Power supply
Fig.1 shows a simplified circuit of
the power supply used in the Philips
196A. The output from the rectifier
and its series 135Ω resistor is filtered
using a 50µF electrolytic capacitor
and is then fed via a 1.6kΩ resistor
to provide the 90V HT supply rail.
This rail is further filtered using 40µF
electrolytic capacitor.
By contrast, the filaments are fed
from the 109V rail via an adjustable
2kΩ wirewound resistor (set at 1.95kΩ
ohms in this set) which reduces the
voltage to 7.5V at 50mA. A 400µF
electrolytic capacitor filters the filament voltage which is then applied to
the 3V4. It’s then filtered using another
40µF electrolytic capacitor before being fed to the filaments of the remaining valves which are in more critical
sections of the receiver.
Typically, the valve filaments were
wired in series so that the total filament
current remained at 50mA. This applied whether four or five valves were
used, with a 7.5V filament supply used
for a 4-valve set and a 9V supply for a
5-valve receiver.
In addition, the filament circuit
has a 270Ω resistor across one half
of the 3V4’s filament (pin 1 to pin 5),
with a 390Ω resistor then connected
to chassis. For those unfamiliar with
series-connected filament circuits,
this may appear to be a rather strange
arrangement.
The first thing to realise here is that
the plate and screen currents of a filament valve go through the filament to
earth, thereby increasing the filament
current by the sum of these two currents. As a result, the 270Ω resistor is
included across half the filament of
the 3V4 so that the currents flowing
through both sections are the same.
The 3V4, which is the audio output
valve, draws around 7-9mA and so this
extra current is “bled” to earth (chassis) via the 390Ω resistor, thus keeping
the current through the filaments of
the 1R5, 1T4 and 1S5 valves close to
50mA. Without this bleed resistor, the
current through these filaments could
go as high as 60mA.
As a result, the voltage across each
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The top of the chassis is neatly laid out, with all parts
readily accessible. The rotary switch at right provides on/
off switching and selects between battery and mains power.
By contrast with the top side, many of the parts under the chassis are
difficult to access. This view shows the chassis after restoration, with all
but two of the paper capacitors replaced.
filament is kept close to the required
1.5V.
Because these remaining valves
have a current drain of just 1-2mA,
it’s not usually considered necessary
to balance the current through their
filaments (and thus the voltage across
them), although some designs do include this.
During the course of my checks, I
found that the 1R5’s filament voltage
was around 1.65V, which is much too
high for the valve to have a long life.
The reason was simple enough – the
390Ω resistor had been incorrectly
wired to pin 1 of the 1R5 instead of pin
7. Once this had been corrected, the
filament voltage came down to the correct 1.5V. Manufacturers in those days
did make wiring mistakes. Sometimes
they are obvious, sometimes not.
There is also one potentially serious problem with this type of power
supply. If a valve filament goes open
circuit, the voltage at the filament feed
point (7.5V in this set) will quickly
rise to well over 100V. As a result,
the 400µF 10V electrolytic capacitor
across this rail will soon succumb and
could even explode.
Alignment
Having corrected the filament supply wiring error, the next step was to
check the alignment.
I began by tweaking the 455kHz
IF transformers for maximum audio
output and found that they were
quite close to their correct settings. I
then checked the oscillator setting by
tuning from one end of the band to
the other and found that it was close
April 2012 85
This view inside the restored Philips 196A receiver shows the chassis with
the bottom cover in place. The 7.5V and 90V batteries fit into the available
space beneath this cover.
enough to not warrant adjustment.
The next step was to slide the tuned
coil along the ferrite rod antenna to
tweak the performance at the lowfrequency end of the dial. Once again,
very little adjustment was needed. I
then tuned the set to around 1500kHz
and adjusted the antenna tuned circuit
trimmer capacitor. It too was close to
its optimum setting.
Finally, I resealed the adjustments
by re-melting the original sealing wax
using a soldering iron.
The set now turned in an excellent
performance, especially considering
that it only has four valves. And with
an external antenna and earth connected, the stations romped home.
An intermittent problem
Unfortunately, the set still had a
problem. Although it generally worked
quite well, it would also occasionally
go completely dead. And to make matter worse, the fault was intermittent.
I checked the voltages at various
point around the circuit when it was
dead and also when it was working and
they were all correct in both situations.
I could also get a healthy blurt from
the speaker if I touched the top of the
volume control, which indicated that
the audio section was working.
I then checked the front-end of the
receiver and although it appeared that
the 1R5 was oscillating, it wasn’t producing any 455kHz output according
to my tuned signal tracer.
Suspecting a faulty valve, I replaced
both the 1R5 and the 1T4 but that
didn’t cure the problem and subsequent tests proved that they were OK.
I then found that when I wriggled
these valves around in their sockets,
Many of the parts
under the chassis are
“buried” two or three
layers down, which
can make replacement
difficult and timeconsuming.
86 Silicon Chip
the set would come good. As a result, I
re-cleaned the contacts as it appeared
that there may have still been some
corrosion on either the valve pins or
the socket pins.
Once that was done, the set worked
quite well for some time but then
suddenly went dead again. This time,
there was no blurt from the speaker
when I touched the volume control,
so the fault lay in the audio circuitry.
Using a signal tracer, I quickly determined that the receiver was working
right up to the output of the speaker
transformer. I then checked the speaker
and it also tested OK, with around 3Ω
of resistance across the voice coil. This
was rather puzzling as the fault had to
be here somewhere, so I re-tested the
voice coil a few times and found that
it had intermittent continuity.
Eventually, I traced the fault to the
spot where the flexible wire joins to
the voice coil winding on the speaker
cone. Unfortunately I couldn’t repair
it, so a new speaker had to be fitted.
Removing the speaker is straightforward. The first step is to disconnect
the wiring to it, after which the front
panel is separated from the chassis by
removing four screws. It’s then just a
matter of undoing the four screws that
hold the 100mm speaker in position
and sliding it out.
I didn’t have a Rola speaker in my
spare parts bin but another, slightly
smaller speaker which I had rescued
from old equipment did fit. And that
cured the intermittent fault once and
for all.
Summary
Although the Philips 196A is a
rather utilitarian receiver, it’s still
quite pleasant to use. It doesn’t have
the appeal of a beautifully-restored
timber cabinet receiver but it’s a somewhat unusual set that’s worth having
in any collection.
It works quite well, especially considering that it’s a battery/mains portable set with just four valves. It’s also
quite compact and the instructions
inside the case are extremely helpful
when it comes to servicing.
Finally, despite its age, there were
relatively few problems – just a dud
selenium rectifier, some dirty valve
sockets, a small wiring error and an
intermittent speaker voice coil. Fortunately, the 1R5 valve in the front
end had survived having a higher-than
normal voltage across its filament. SC
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