From: newsq@ampex.com (Stan Busby)
Subject: Busby Chronicans, Tales of early radio repair
Originator: wdp@gagme
Organization: Ampex
Date: Wed, 14 Oct 1992 19:56:19 GMT

 
My first paying job was working in a radio repair shop after high
school and full time during the summer vacation.  The shop was on
the third floor of a company named the Morris Music Co., on the
main drag of Portsmouth, VA about a block away from the ferry
terminal to Norfolk, VA.  They sold furniture, pianos, (I think),
and lots of radios.  The repair shop did not deal with the
public...the sales folks downstairs did that.  This was about 52
years ago.  At that time there was no FM and no stereo.
 
Small radios were mostly 4 or 5 tubes with the cathode heaters
connected in series.  Some used a power cord with Nichrome
resistance wire wound around it as part of the heater power
circuit, while others used tubes with fairly high heater voltages
(35Z5, 50L6, etc) such that the heater current was a standard
0.15 ampere for all types, and the sum of all the voltages came
to 115 (or so) volts.  A few used a "ballast" tube, which was
just some resistance wire inside a bulb.  This kept the heat
inside the cabinet.  The idea was to avoid using a transformer,
which was a high-cost item.  Most used tube-type power
rectifiers, but some used selenium rectifiers.
 
You have probably smelled hydrogen sulfide, the smell of rotten
eggs.  When a selenium rectifier flames out, there tends to be a
little hydrogen selenide in the air.  It is an awful stench.  I
am told that the smell of hydrogen telluride is unbearable.  (The
three elements Sulfur, Selenium, and Tellurium are all in the
same column of the famous periodic chart of elements)
 
Lots of people kept their large floor-cabinet radio in the living
room, and had a small set in the kitchen.  Usually these had no
"back", so as to improve the cooling.  Mice and roaches just love
warm vacuum tubes.  The mice urinate on them.  Thus there is a
layer of dust and roach feces embedded in dried mouse piss, along
with layers of slimy bacon grease condensate.  Both the mice and
the roaches liked to eat loudspeaker cones and insulation.  In a
few cases it got so bad that the crud got between the plates of
the tuning capacitor and shorted it out.  Mouse piss is mildly
conductive.
 
The larger receivers had a power transformer, a fairly large
loudspeaker and perhaps a "tuning eye" an early prototype of a
cathode ray tube. (6U5)  It was typical for the inductive part of
the power supply ripple filter to be the wire-wound magnet of the
loudspeaker.  (less cost) As this introduced some hum into the
speaker, there was often a small secondary coil arranged to
cancel the hum field.  It was called a hum-bucking coil.
 
If you lived in the boondocks, you didn't have AC power.  Rural
electrification was just beginning.  You had a radio with a
cabinet which was big enough to hold the radio and its battery. 
The battery had three parts, A, B, C.  A was 1.5 volts, the
filament supply.  B was between 135 and 67.5 volts and I forget
what the C voltage was (probably -6 volts or so).  It was used to
bias control grids negatively.  They were expensive to operate
because batteries cost so much.  
 
Another battery-operated receiver was the automobile radio.  It
worked like most other receivers, except that there was a plug-in
vibrating reed switch which served to alternate the polarity of
the auto's battery feed to the primany of a power transformer. 
The vibrator was sealed inside a tin can and covered with sponge
rubber so you wouldn't hear it.  Some of them had an extra set of
contacts on the vibrating reed which were used for mechanical
rectification of the high voltage out of the transformer's
secondary winding.  Much later, when autos switched to 12 volt
batteries, there was a line of tubes that would actually work
adequately with 14 volts of anode voltage, negating the need for
a power transformer and vibrator.
 
>From the service standpoint, there was a frustration syndrome
which grew as the boondocks were electrified.  Clem Grassroots
was smart enough to buy himself a good AC powered radio so he
wouldn't have to buy batteries, but he was smart enough to keep
the old battery one around.  Typical receivers of the day used
tubes with a cathode heater voltage of 6.3 volts, thought to be
the average voltage of an 6-volt automobile battery.  (there was
later a 7XX series of tubes with a nominal heater voltage of 7.2
volts.  They had a special "lock-in" pokey-out thing on the base,
shaped to lock into special tube sockets so they wouldn't jiggle
out.  I won't get into the shape of the thing except to say that
it appears to have been circumcised)
 
Anyway..sooner or later Clem's new radio dies.  He figures, quite
properly, that a tube has failed.  He goes to his old battery set
pulls out the tubes, and one by one plugs them into various
sockets of the 6.3 volt set.  One by one he zaps the 1.5 volt
filaments.  The 1.5 volt and the 6.3 volt series tubes shared the
"octal" base.  There were eight pins even if not all were used. 
There was a keyway molded in which reminds me of the keyway on an
outboard motor propeller drive shaft.  It would plug in only one
way.  But you could still screw things up by plugging the wrong
thing into the wrong socket.
 
The other syndrome we were aware of is the handyman who has a go
at making his radio work.  He pulls out the chassis, and proceeds
to tighten up all visible screws, thereby detuning everything. 
 
We were fastidious in our shop.  Every radio, regardless of how
simple or complex, was completely aligned.  That is, set the low
frequency and high frequency trimmers, align the intermediate
frequency transformers, etc.  Even bend the little "wings" on the
tuning capacitor to make the local oscillator "track" the RF
amplifier stage(s). Because the plastics of the day were early
compounds, they tended to age quickly, especially if exposed to
sunlight.  Each radio was examined and the AC line cord replaced
if the old one way fraying, or the plastic was cracking and
exposing bare wire.
 
One day, with a big work-load, a receiver landed in front of me
with a crumbling line cord.  It was Monday morning.  I whipped
out my dikes (diagonal cutters) and chopped off the line cord. 
But I forgot to unplug it first.  In that sparkling moment of
electric spasm, before the circuit breaker dropped, I invented
wire-strippers.  I did not apply for patent.  Actually they
became very good wire strippers.  They would strip two wires at
once.
 
In those days, one did not arbitrarily replace a loudspeaker. 
Labor (at least mine) was cheap.  If the cone was intact, one
unglued the rim of the cone, and the voice coil support (the
spider), using a solvent, and unsoldered the wires to the voice
coil.  The voice coil wires were then unwound and discarded. 
Using some round thing of the appropriate diameter as a mandrel
(an electrolytic capacitor usually, but I have used a
broom-stick), you wound a new voice coil, painted it with acetate
glue, and after it was dry, wound a turn or two of paper around
it, inserted it into the gap between magnet and pole-piece and
re-glued the cone and the spider.  Later pull out the paper,
connect the litz-wire to its terminals, and there you are...as
good as new!
 
In the case of damaged cones, I have applied, with the tenderness
attributable to a surgeon, a kind of poultice swimming in
testor's cement, of ordinary paper, so as to bridge gaps eaten
away by mice and roaches.  Only if the damage was more than say
30% of the speaker cone would I give in and replace the cone.  In
the war years it was difficult to obtain spare parts, like
speakers.  It could take months to obtain an exact replacement. 
One improvised.
 
The really fancy radios had record players built into them.  All
78 rpm, lateral cut (not hill-and-dale like Edison did).  The
pickup device was almost always a piezoelectric crystal made of
Rochelle salts, which are very hydroscopic.  Even though it was
coated with black water-proofing gunk, over time water vapor
would leak in.  Ours was a river town and very humid in the
summer.  The crystal would dissolve in its own water of
crystalization and wasn't piezoelectric any more.  You could get
steel needles or needles made from cactus spines.  The steel ones
lasted, but the records didn't, while the cactus ones wore out
but didn't scrape up the groove as much.
 
There were two kinds of record players then.  With type one, you
put a stack of say 4 records on a spindle.  Side one was dropped
onto the turntable and played.  When the needle hit the
off-center circle near the inside, this tripped the mechanism and
side two was played.  After the four sides were played, you
lifted off the stack, inverted the stack, put them back on the
spindle and play the last four sides.  In this configuration,
side eight has to be on the back of side one, side seven on the
back of side 2, and so on.  Some fancier turntables had two
spring-loaded pickup devices.  The record was clamped and driven
by a small pair of platters of small diameter.  Side one was
played by the pickup facing downward, then side two was played by
the one facing up.  In another scheme, a mechanism flipped the
record over to play side two.  In any case, for long classical
recordings you usually had a choice of "side" configurations when
you bought the album.  The idea of the 1-2, 3-4 etc scheme is
that you didn't have to get up off your lazy butt to flip the
discs.
 
You must know that in the fighting of a war, the information fed
to the populace is a top political priority.  (Please read the
book "Public Opinion" by Walter Lippmann).  In those days, butter
was rationed, vacuum tubes were not.  You could get through to
most of the people on the radio, and those who didn't listen, you
got through to by holding back some butter.  He who controls the
minds of the populace wins. Churchill knew it, Roosevelt knew it,
and Stalin knew it.  RADIO WAS IT!   
 

Newsgroups: rec.radio.broadcasting