Let's take a break from microphones and this time take a look at another essential piece of broadcast equipment...the turntable.   

From the earliest days of radio the phonograph turntable was used to provide programming material for stations.   It was pretty primitive early on when they would just put a mike in front of an old horn-type phonograph set.  It wasn't long until more sophisticated types of record reproducing equipment were developed. 

Somewhere in the 1930s RCA designed a very high quality turntable unit that became a standard of quality in the industry.  The RCA Model 70 direct-drive turntables were continually improved upon through the years and were in use at many radio stations clear into the 1960s. 

Before we get into specifics about the RCA unit...maybe a little info about turntables in general might be in order.  Several equipment manufacturers built broadcast quality turntables...companies like Fairchild, Gates,  Rec-O-Cut, Presto, Western Electric, QRK and others.  Most of these units were “rim-drive” type turntables...but a few made, the more expensive, direct motor drive type.

My career in radio began in the late 50s when virtually all radio stations used turntables to play vinyl records on.   I say this because many of the modern-day radio folks have probably never seen a turntable in a radio station!   I was still playing records on turntables when I left radio in 1989...which doesn't seem that long ago!   I worked in TV for several years doing scheduling work and some voice announcing and then retired.  After about a year or so I had the opportunity to go back to work in radio to find that the turntable had been replaced by computers!  All the music that you hear today on radio is on computer hard-drives and it's very rare to see a turntable or even a tape machine in a radio station.

But let's go back to those “golden years” of radio when the turntable was king of the control room!

When the RCA direct-drive turntables first came out there were two speeds used to play recordings...33 rpm and 78 revolutions per minute or RPM.  33 rpm recordings were generally called “transcriptions” and were usually 16 inches in diameter.   They were not like the later 33 rpm “LP” commercial records
that came out around 1950.  These recordings were made with what was called a “standard” groove like the 78 rpm records of the day.  This “standard” size groove was larger in width than the later “microgroove” LP records of the “hi-fi” and stereo eras...so the pickup “needle” or stylus had to fit this wide groove.

These transcriptions were specially produced recordings by large companies especially for radio stations and not the general public.   There were music libraries that stations could buy or subscribe to  to augment regular phonograph records for music programming.  Transcriptions also were used for  airing other types of syndicated radio shows of all kinds. 

Remember tape recording did not come into use until after WWII...so recordings played on turntables were about the only way to get recorded audio on the air.  Many radio stations had special machines that could “cut” their own recordings of programming right at the station. RCA made cutting head units that fit right on their direct-drive turntables.  These recordings were cut on recording “Blanks” which were aluminum discs coated with an acetate material that was fairly soft for the cutting needle to cut the grooves to impress the audio signal on the disc.  Because the record-blank material was soft these recordings could only be played back a few times...the playback needle would soon scratch the grooves so they would be not playable.

As mentioned, radio stations also played regular 10 inch 78 rpm commercial phonograph records on these same turntables...hence the two available speeds. It wasn't until around 1950 that the 45 rpm small record with the large spindle hole came into use and eventually replaced the 78 speed. 

With that bit of background now we are ready to take a closer look at the RCA model 70 turntables.   

These turntables were built into a large floor-standing cabinet.    The motor was located on the bottom shelf inside the cabinet and drove the 16 inch diameter turntable through a long shaft with a flywheel  that connected to the bottom of the turntable.  There were also flexible couplings and clutch in the drive shaft to isolate the platter from the motor.  The unit had a motor on-off switch mounted on top of the cabinet and there was also a mechanical speed selection lever located on the outside rim of the turntable.  This unit was capable of very smooth starts and stops.   The platter had a felt covering to allow records to be “slip-started” when cued up and ready to go.

The top surface of the cabinet was covered with a black linoleum that was “cigarette burn proof”...people smoked just about everywhere in those days!   The cabinet itself was painted RCA “Umber-gray”.  

Of course, to play records you need a pick up arm and RCA supplied a sturdy looking arm that had  a magnetic pick up cartridge that plugged into the arm.   The stylus or “needle” was a diamond for long wear...but when it needed replacement you had to send the removable cartridge back to RCA for replacement which was not too convenient.   A station would normally have extra pick up heads on hand to enable continued usage.

RCA Records came out with the new 45 rpm record around 1950...so the RCA broadcast equipment division had to make available a kit to convert existing model 70 machines to play this new speed.
This kit provided a ball-type speed reducer which installed between the two flexible couplings on the main drive shaft.  An additional switch was added so you could select either 78 or 45 rpm.  Since the 45 rpm records used a smaller groove RCA had a “fine-groove” tone arm available that was installed on the cabinet top to play either 45 or 33 rpm LP records.  Now the turntable had two pick up arms...good thing they had plenty of room on top of this large cabinet to make this alteration!  Another switch had to be installed to select between these tone arms.

The turntable cabinet was quite large and so there was plenty of room inside for mounting equalizer units and a preamplifier.  The RCA pick up heads were low impedance and required a passive equalizer for proper operation.  Depending on the stations control console facilities, the engineer would usually connect the output of the equalizer directly to a microphone input.  Alternatively the engineer could mount a separate preamp in the cabinet just for the turntable and feed it to a high-level input on the board...this would free up the microphone preamps for microphones.

The passive equalizer units had a switch mounted on the top of the turntable cabinet that allowed the operator to choose various playback curves for the records played.  Normal records were cut laterally but some transcriptions were cut vertically so there were different equalization positions, as shown  in the illustration, for different types of record playback.   There were also equalization positions for noisy or scratchy records.  The old 78 records were made out of shellac and were very hard and brittle....easily broken...and rather “hissy” of “scratchy” sounding sometimes.

Before airing a record the operator would have to “cue-up” the record.  He would switch the console channel to “audition” or a cue channel and let the record play to the first sound, stop the motor...then he would carefully, with his hand, back up the record to about a quarter of a turn before the sounds starts.  When the time came to play the record on the air the DJ or engineer would hold the record with his hand to keep it from turning as he started the motor...then he would open the volume control “pot” and let the record go and it would be on the air.

Modern-day live club Djs sometimes use vinyl records and do this “cueing” back and forth getting a “scratchy” sound that they actually enjoy hearing and making a part of the show!  Radio Djs never wanted to hear any scratch on the air!

The RCA model 70 turntables were a big part of radio back in the day...they were “built like a battleship” and served faithfully for years and years.   KYOS in Merced used the model 70s...in fact when I worked there, from 1959 to 1961, I used to cut the station jingles and other short program elements to discs on an RCA machine so they would be easier to handle on the air rather than having to cue up reel to reel tapes.   This was before the station had endless-loop tape cartridges that were just coming into use about that time.

Enjoy the pictures of the RCA model 70 turntables and we'll catch you next time.


This is a page from the 1951 RCA equipment catalog showing and describing the model 70...as you can see RCA was very proud of it!  

Click here to enlarge.
Here is a model 70 showing the 2nd RCA “fine-groove” pick up arm mounted allowing this turntable to play microgroove LP and 45 records.  Notice that it is smaller and looks much lighter weight than the older standard groove pickup on the right.  The control board in the picture is the famous RCA model 76 tube-type console dating from the 40s with an art deco RCA “on-air” light on top.  (Chuck Pharis)

Here is the record cutting attachment with a recording blank on the turntable.The actual cutting needle was very sharp and left a long thread of cut material in its wake as it cut the record...you had to be very careful not to get the thread caught back under the needle...if it did the recording was ruined!

A catalog page showing the 45 rpm adapter kit.  It says it's easy to install...but I think many an engineer probably pulled a few hairs out doing it!  Click to enlarge.
Here is a DJ reading his script on the air as he holds the next record on the felt turntable surface waiting for the moment for the record to hit the air.  (U of Maryland lib. Of Am. Broadcasting)
Here's a happy DJ getting a platter ready to air.  Notice he has horse collar type harness around  his neck supporting an RCA 88A mike....keeping him close to the mike no matter how he moved...must have been pretty heavy after a long air shift!! (U of Maryland Lib. Of Am. Broadcasting)

Part 6
Here's a wild and crazy DJ at WHFB in Benton Harbor Michigan and RCA turntables.  (U. of Maryland Lib. Of Am. Broadcasting)

Here is a photo of me in the KYOS, Merced studio in 1959.  I was a fresh 20 year old kid at my first radio job.  Right behind my head is an RCA model 70 turntable with the record cutting attachment mounted on top.