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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 distortion 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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SAMs
Photofact Illustration Showing Eccentric "Power Cam":
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 1-3/16" ID (inside diameter)
x 1/8" thick was a fine replacement
tire.
The only problem
was that 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, then the appropriate record button
is pressed. WHILE holding down the record button, one must 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.
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.
The "Tuner on-off" switch
controls the input to the tape recorder. When "off", it accepts signals through
the microphone jacks and sends the output signal to the wing speakers, when
"on" it accepts signals from the line-input jacks (on the back
of the machine) and sends that signal to the wing speakers. The tape recorder
can act as an amplifier for a tuner module. 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
speaker "on-off" switch does exactly what it says, allows the wing speakers
to sound or cuts off power to them. The headphone jack 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 helps
prevent "feedback" when occurring 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 -->
Please
note that ClydeSight Productions DOES NOT rebuild or sell vintage
reel to reel tape recorders, nor can we help anyone involved in such a project.
The tape recorders shown in these pages are part of a personal collection
and are not for sale. We Do Not recommend
that unqualified or inexperienced persons attempt to restore vintage audio
equipment.
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www.clydesight.com Master Site
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Productions - 2007
