This is the "Historic City" Section of
The Broadcast Archive

Maintained by:

Barry Mishkind - The Eclectic Engineer
Last Update 7/1/03

Hi... Welcome to a really interesting page.  This will grow and probably take a while to load, as we add more pictures of vintage stations and their equipment. Of course, this all will happen if we get more of these pictures.  Please help!


This is a look at the Master Control for WCCO around 1960.

Mark Durenberger recalls:

My guess is that this was taken late 50's or early 60's. The Ampex 350's would set the date. They were probably new when this photo was shot; the metal reels in use were very early versions. (A few years later, WCCO engineers milled the hubs a few millimeters narrower, to eliminate tape wrap at high speed.)

You can see only 7 of the 11 racks in Master Control. The first two unseen racks contained monitor and control gear for the Western-Electric Doherty transmitters, including a custom-built remote-control system. Rack 3 on the left contained several bays of RCA tube amplifiers (these were the guys with the chrome-plated transformers). Note that the amplifier bay swing-down doors have tiny "CBS" labels; CBS built this plant when they owned the station. Those tube-amplifier bays were replaced in the mid 60's with BA-series RCA solid-state amplifiers; that move was the first step toward adding serious grunge to the audio.

Rack 4 held the famous "Studio 5"; the mixer you see just above the table. Studio 5 was the heart of the station. That mixer had 3 mike faders; one in a newsbooth ("Studio 6") and two in the main announce booth ("Studio 5"). One fader was CBS Radio, one was an "ET Bus," the others were for remotes and telephone. The mixer itself was passive; electronics were in adjacent racks. I'll come back to the ET bus; it's pretty interesting.

Rack 5 (with the clock) held the output distribution pre-selector and the monitor selectors. Just below the clock are three monitor selectors and volume controls driving various overhead speakers. The monitors were deliberately separated across the room, so as to be available as either foreground or background monitoring, depending on what the engineer was focused on at the moment. Beneath the volume controls is the 6 x 5 pre-selector. This was a bridging matrix used to feed various networks from up to 6 sources (called "Studios," even if they weren't studios). You would "pre-select" a scheduled feed combination of all studios to all outputs, using the "off side," and at the "take" moment, you'd push a single button, for a salvo switching to the new feed combinations. The "off" side would then become the "on" side. It was all passive, using high-quality telephone reed relays. The 4 VU meters and their attenuators monitored outbound trunks fed by the "studios" grabbed by the pre-selector.

Rack 6 contains the remote-loop selectors and equalizers. Note the passive equalizers that you'd dial in, using the rotaries near the top. 12 trunks from the telephone company could be assigned to either the "X" bus or the "Y" bus. You could pre-equalize the loop assigned to one of the busses, while the other bus was on the air. 12 trunks was more than enough for us to handle; the phone company test board was actively pre-selecting from several dozen loops to be fed to these 12 trunks. At the bottom of the bay in rack 6 is a row of telephone trunks complete with ring-down arrangements. Push a key UP to grab one of the handsets beneath the table; down for the other. "Ring-down" push-buttons allowed you to instantly connect to the toll-test board or the local telco wire office.

Rack 7 has some test gear below the Ampex; there's an attenuator panel, oscillator and passive distortion bridge. Rack 8 MAY have held an input panel for disc cutters replaced by the Ampexes. You can also see some current meters that were used to test tube conditions in the amplifiers without taking them off-line.

At the bottom of rack 8 is a typical "A/B" switch that transferred the relay control voltage from 'regular' to 'emergency.' (I have to tell a short story That switch got us in serious trouble one night when we lost power during a tornado. The janitor had bumped a similar switch under rack 3 ; we couldn't see it was in the wrong position. When the storm came through and the power barfed, the emergency power came up fine; studio lights worked; amplifiers and VU meters were lit up. But we couldn't get the mikes on!)

I mentioned there were two more racks on that end (10 and 11). They contained monitor amplifiers and a third Ampex 350. The photo is taken by someone standing against the turntable bay; there were 3 of the old RCA knuckle-crackers in a row, just far enough away from the racks to require a chair with good casters if you were alone (overnight). Each turntable had two 16-inch pickup arms; one had a 3-mil stylus to play the acetates that we used to record all of the spots; the other was a 0.7-mil pickup arm for stereo vinyl. (WCCO had an affair with carts very early on...and got burned by the lack of reliability. So they stayed with acetate (cold-stylus to boot!) until the new control room went on the air in 1977!)

Each turntable had its start switch on its own fader. A twist of the knob put the turntable on the air via the ET Bus. Each of the three turntables (and in fact each of the dozen or so tape machines around the place) had its own separate cue amp, volume control and speaker. Again...the spatial separation of the speakers and their location next to the appropriate machine helped the engineers when it got very busy in that room.

In the complex of the 60's there were five "consoles" in various rooms, interconnected via the afore-mentioned "ET Bus." That bus was a passive, low-impedance balanced "trunk" that began in a distant studio and ended up in the Studio 5 mixer panel. Any turntable or tape recorder anywhere in the complex could immediately go to air by operating a red key next to that machine (the "B Key"); that would immediately connect it to air, via this trunk. That feature was very useful on more than one occasion, when a lot of audio was coming in, and we had to get it to air quickly.

In the days before adaptive hybrids, WCCO did a lot of pioneer work in what we once knew as the "balanced-level" phone mixing method. We actually re-created telco repeater bays; even called them by their geographical ports as did the phone company. We got very good at mixing mike and phone to air. It required constant gain-riding, but the quality of the mix and the phones on the air on WCCO was incredible.

There's much more to this story.


This transmitter was built by John Fetzer for use on WKZO 

International Broadcast Manufacturers:

France - Sofratec