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Wollensak 5750 Vintage Reel to Reel Tape Recorder Restoration
Internal View -
Control Central

 

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Wollensak 5750 control central interior

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The Wollensak 5750 vintage tape recorder has special area called "ContrCentral". This part of the machine controls all the levers and idler wheels and includes the "power cam" and combination erase/record/playback head. It is essential to the operation of the machine and anything "wrong" here will render the playback or recording functions useless. This page discusses the "Control Central" parts of the Wollensak 5750 reel to reel tape recorder and what parts I had to replace or adjust to get the machine into good working order.

<-- To Left - Feed Reel Section  |  To Right - Take Up Reel Section -->

 

Wollensak 5750 Vintage Tape Recorder "Control Central" Concept

This is the most unique approach to a reel to reel tape recorder design I've ever seen. It's an amazing balance of forces. Everything here is driven by springs. The transport plate - which holds the pinch roller (black small rubber wheel) and head pressure pads (white spring loaded plastic rods with red felt pads on the end) - is always drawn forward by the two strong springs attached to it. (These springs are the ones with the plastic muffler sleeves on them.) The "power cam" is what moves the transport plate into and out of position. The end of the transport plate engages the reel brake arms and the take up reel clutch.

All the pushbuttons do is release hold back catches. Here's how it works:

Start Button

Pressing the Start button (this works in record mode as well) releases the transport plate to the power of the 2 large springs through a release catch, which "lets it go".

The "power cam" tire presses against the capstan shaft, which causes the cam to rotate where it engages. The capstan shaft has a "knurled" portion, far below where the tape runs, to grip the power cam tire and turn the cam. As it rotates, because it is eccentric (i.e. oval shaped) and is fixed by an axle at one end to the transport plate, it allows the transport plate to release the reel brakes and gently engage the pinch roller and pressure pads against the capstan and combination head.

The transport plate is then caught by a catch under the Stop button which holds it from going any further forward.

The "power cam" is turned slightly away by the capstan shaft so it no longer is engaged. This is a really tricky move, and the "power cam" has a friction bearing to prevent it from turning too far away from the capstan shaft because it is going to be needed by the Stop button.  Pressing the Start button now will have no effect; the transport plate is beyond the release catch.

Pause Lever

There is a "pin" affixed to the underside of the transport plate.

Pulling the Pause Lever forces a piece of metal against the pin, and this pulls the transport plate away from the capstan shaft as the Pause Lever is pulled down.

As the transport plate moves back, it releases the reel brakes to stop forward motion of the tape.

In the Wollensak 5750 EV (Early Version), the Pause Lever does not move the transport plate far enough back to re-engage the Start button release catch, so it does not provide a "manual over ride" for the mechanism. I don't know if the LV (Later Version) altered this arrangement.

Releasing the Pause Lever allows the transport plate to return to its previous position, which engages the pinch roller and pressure pads as they were before, and releases the reel brakes.

 

Stop Button

This releases the transport plate to the influence of the two large springs again.

In the EV (Early Version) of this vintage tape recorder - which I have - when the Stop button is pressed, a release catch lets go of the transport plate, allowing the springs to pull the it even closer to the capstan shaft and combination erase/record/play head!

The "power cam" gets in the way and its "tire" engages the capstan shaft once more. Because it is eccentric, as it rotates, it forces the transport in reverse, back toward the control buttons until it is caught by the release catch under the Start button. By this time, the "power cam" has rotated almost it's full apogee (or would that be perigee?), and it turns just a bit more to disengage from the capstan shaft.

Of course, the tape is still moving through the mechanism past the combination head, (until the reel brakes take hold) so the change in speed and strain on the mechanism is heard as audio "whoop" through speakers or headphones.

According to a SAMs Photofact book, which I ws able to purchase from Stereo Manuals.com, the Wollensak 5750 LV (Later Version) had additional parts and a different pressure pad and pinch roller assembly which may have fixed this disturbing problem in the EV by disengaging the pressure pads and tape guides from the combination head and shutting off the audio function momentarily.

When the Stop motion completes, the transport plate is now ready to be released again by the Start button. Pressing the Stop button at this time does absolutely nothing because the transport plate is nowhere near the Stop button release catch.

Now if you're confused, I don't blame you. It doesn't help much that the "power cam " is underneath the transport plate. But the following images should make things a bit clearer. Note, the "power cam" does not share the same axle as the pinch roller, although the perspective of the drawing makes it appear that it does.

Transport Plate and Power Cam:
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Wollensak Transport Plate and Power Cam In Action

 

SAMs Photofact Illustration Showing Eccentric "Power Cam":

Wollensak Transport Plate and Power Cam In Action

Restoration/Rebuild

"Power Cam"

The "power cam" is key to the whole operation, and in the Wollensak reel to reel tape recorder I purchased on E-Bay, it was not functioning. The problem was that the "tire" had hardened and broken off the cam. The cam itself is made of plastic (which fortunately is in good shape, if a bit discolored-- it's supposed to be a creamy white).

I looked at the cam and decided that I could get a replacement "tire" at the hardware store by purchasing a plumber's "O" ring. My local ACE Hardware store had a large selection of plumber's parts, and I found that the DANCO "O" ring #16 with the dimensions: 1-1/16" (outside diameter) and 13/16" (inside diameter) by 1/8" (cross section) was a fine replacement tire. A slightly smaller diameter "O" ring could also work, as long as the cross secion dimension is 1/8" because this is the "gripping" part of the tire.

The "O" ring is lubricated (for obvious reasons.) I "degreased" it with a detergent wash and then gently roughened the surface with #220 sandpaper to give it better grip. It worked perfectly.

Pinch Roller

The pinch roller is essential to smooth tape movement with the capstan shaft and good audio quality. In my Wollensak 5750 vintage tape recorder, it had "flat spots" because the machine must have been stuck in the "Play" position for quite some time. I sent it to Terry of Terry's Rubber Rollers and he resurfaced it perfectly.

The Wollensak 5750 EV manages the pinch roller with a free floating axle (something I have never seen before), held in place by two arms of the tension spring. This ensures that the roller always contacts the capstan shaft in perfect alignment, so there is no problem of "tape creep", which happens if the pinch roller is out of alignment with the capstan shaft. In the SAMS Photofact illustration above, the axle is part number 68 and the spring is part number 67. It is obvious that the axle is able to slide in slots made for it in the transport plate and the pinch roller support bracket.

Pressure Pads

The pressure pads hold the tape in contact with the combination erase/record/playback head. The design in the Wollensak 5750 EV is very unusual, using sliding arms to carry and position the pressure pads, instead of a "flip up" or "flip over" plate that can be found on many other tape recorders of the time.

The machine I bought from E-Bay had worn out pads. The pads themselves, located on the ends of the little plastic sliding arms, part number 66 in the SAMS Photofact illustration, were made of a black felt and worn and dried. I replaced the pads with Piano action felt which is red. This is a smooth, "hairless" felt used in piano actions for various parts, and is extremely durable.

Record Lock-Release

The record lock-release feature of the Wollensak 5750 tape recorder is also quite unique. There are two record locks located on each side of the pushbutton section of the tape recorder, one for the left channel, one for the right channel. They are not labeled on the machine.

The record lock-release normally blocks the record button from being pressed.

To allow the record button (left or right channel, they are independent) to be used, the record lock-release is pressed inwards, and whiler being held in, the appropriate record button is pressed. WHILE holding down the record button, release the record lock, then the record button. The record lock must be released first or the record button won't "catch".

The record lock also releases the record button - at any time, even when the machine is running a tape.

Pressing the record lock-release when the record button is engaged will disengage the record function. This automatically takes place when the machine is put into STOP, REWIND or FAST FORWARD mode.

In the lo-res animated gif below, The right record button has been engaged. When I press the record lock-release button, the record button is released.

Wollensak tape recorder record lock feature.

When the record buttons are activated, the output of the tape recorder (monitor function) is attenuated, but the meters register correctly.

The rest of the items in the "Control Central" area are more standard.

There are two concentric volume/tone controls - a common arrangement at the time in audio equipment.

The two VU meters are similar to those found on portable and battery operated tape recorders of the time made by Philips (Norelco in the United States). Wollensak calls them precision meters, but there are no DB markings, just a black and red area.

The 'up-down' working "Tuner on-off" switch (top of the Control Central) is a mis-labeled part. There is an optional tuner module, which is what they must have been considering when they designed the machine and made the label on the outer bezel. This switch should have been labelled "Line/Mic" because it actually turns on and off the "line inputs" to the tape recorder.

When "off" (lower position), it accepts signals through the microphone jacks and the tape head in playback and sends the output signal to the wing speakers (if the speaker switch is on) and headphone jack.

When "on" (upper position) it accepts signals from the line-input jacks (on the back of the machine) and sends that signal to the wing speakers and headphone jack. The tape cannot be heard when the switch is in this position. Thus, the tape recorder can act as an amplifier for the tuner module and any other line input device. This can be useful for "A-B" comparisons during playback.

Wollensak did make and sell a separate tuner unit stylistically matched to the 5000 design series. It is most usually seen in ads for the 5800 model. 

The side-to-side working "speaker on-off" switch (below the Tuner on/off switch) does exactly what it says, allows the wing speakers to sound or cuts off power to them. The headphone jack is always "live" and does not automatically cut power to the speakers. One can listen to the reel to reel tape recorder on headphones and on the speakers at the same time! The on-off switch also helps prevent "feedback" when recording from a microphone.

The next page will describe the Fast Forward/Take-Up reel section of the Wollensak 5750.

<-- To Left - Feed Reel Section  |  To Right - Take Up Reel Section -->

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