Here's what I've got for the Scully variable pitch system, transcribed:
SCULLY AUTOMATIC FEED CONTROL
The Scully Tape Operated Automatic Feed Control provides groove expansion (fewer lines per inch) in anticipation of an extra loud or heavy bass passage during disc mastering of tape recordings. The assembly consists of:
A - A feed motor control assembly and dial actuated potentiometer. The motor assembly mounts on three studs, the holes for which are drilled in the variable feed panels of all Scully machines. The potentiometer is gear driven from the large textolite intermediate gear under the variable feed panel. The motor clutch (small knurled knob on top of main feed dial knob) also acts as a dial lock when the automatic feed is not in operation.
B - A "Maximum Line Adj." panel (3 1/2 x 5") with potentiometer attached. This panel is mounted to the right of the variable feed panel on the tabletop of the machine. When the clutch knob on the variable feed control knob is tightened and automatic unit is in operation the Maximum Line Adjustment knob is used to set the main dial at the maximum number of lines per inch to be cut.
C - A tape pre-amplifier which samples the program material from the advance head on the tape machine. This unit contains the input "Gain" control, "EXCURSION" control and the "RETURN" control. The tape head feeding the amplifier is mounted in such a position as to reproduce the program material in advance (one or two seconds) of the disc recording head and thus a change of feed occurs in anticipation of the changed program amplitude. While the feed change is generally under the influence of the low-frequency content of the program material, it also responds to the extremely loud passages throughout the entire range of frequencies. The pre-amplifier has been equalized so that the low frequency response will provide the initial anticipation control. The anticipation amplification is approximately twenty DB greater in the 50 - 60 cps range, being normal above approximately 750 cps. If desired, the recording engineer can alter this response by a change in the termination across the output of the advance tape head.
1. The Gain Control adjusts the amount of signal coming from the tape head into the system.
2. The Excursion Control determines the amount of decrease in the number of lines per inch for a particular recording. For example: if the Maximum Control knob is adjusted to read 300 lpi on the feed dial then the Excursion adjustment can be set to give feeds of 300-250, 300-200, 300-150 etc.
3. The Return control adjusts a time delay network in the output of the signal control rectifier. The delay in returning the feed from coarse to fine allows the continuance of a sufficiently coarse line to prevent post-groove over-cut. The initial factory setting of the return control network is critical and the coarse adjustment potentiometer in this network should not be disturbed unless it is found to be absolutely necessary. (Voltage change from max. to min. position of Return control is about 0.8 of a volt.)
Screwdriver adjustments are provided in the pre-amplifier for the Grid and Balance pots which are set at the factory to read 5 to 7 volts from arm of pot to ground. The phase modulator tube (6SN7-GT) provides, at the balance point of the potentiometers, phase variations in the AC motor supply for the proper speed and direction control of the feed adjusting assembly The balanced output of the phase modulator is applied to the input of the power amplifier.
D. The power amplifier is housed in a rack mounted chassis together with the follow-up potentiometer power supplies. The potentiometer power supply units provide regulated DC voltages for the "Maximum Line Adj." (Manual on schematic) and the motor-driven potentiometer (Auto. on schematic) which is geared to the variable feed control assembly of the recording machine. Feed-back voltage is taken directly from the servo motor input terminals to provide a damping control for the overall servo mechanism. Screw driver adjusted potentiometers are reached through the front panel to provide control of motor damping (FB) and limit adjustments for the Max Line Adj. potentiometers.
TO PLACE AUTOMATIC FEED CONTROL IN OPERATION
1. Release spring adjusting nut "A" (Fig 11 Instruction Manual) so that no pressure is brought to bear against idler.
2. Plug in all cables, set Gain at zero and Excursion at maximum, turn power on and tighten knurled knob on top of main dial knob.
3. The Main Dial Pointer (trimmers for which are labelled "Auto 70" and "Auto 400" on the Power Amplifier) and the "Maximum Line Adj." potentiometer (trimmers for which are labelled "Manual 70" on the Power Amplifier and Manual 400 on socket bracket under tabletop) must be balanced in order to prevent the "Maximum Line Adj." potentiometer from driving the Main Dial Pointer against its limit stops at either the 70 lpi or 400 lpi settings. If this condition exists the clutch clamping knob will either loosen or become excessively tight. If it is found that the main dial pointer tends to overshoot when the "Maximum Line Adj." control is turned to its limit in either direction, proceed as follows:
(a) - Rotate "Maximum Line Adj." potentiometer slowly until Main Dial Pointer is at 70 lpi and do not let pointer hit stop.
(b) - Adjust Auto 70 pot in Main Amplifier to bring pointer to 72 to 75 lpi.
(c) - Rotate "Maximum Line Adj." potentiometer counterclockwise to bring Main Dial Pointer back to 70 lpi.
(d) - If the limit of counterclockwise rotation of "Maximum Line Adj." is reached before Main Dial Pointer reaches 70 lpi, adjust "Manual 70" pot on Main Amplifier to bring pointer to 70.
(e) - If the limit of counterclockwise rotation of "Maximum Line Adj" potentiometer is not reached, repeat procedures 2, 3 and 4.
(f) - The same procedure as above is followed in adjusting the 400 lpi setting. Once set it will be found that the Manual 400 Adj. (located on socket bracket under machine) will be used for most operational corrections. When properly adjusted Main Dial Pointer can be rotated by means of the "Maximum Line Adj" control in either direction to fully sweep the dial without touching the stops. Leave Dial Pointer at 400 lpi.
4. To test operation, run output of advance tape head to input of pre-amplifier. Run modulated tape through advance head. Set "Excursion Adj." to its maximum (right hand) position. Adjust preamplifier volume control until Dial Pointer follows variations in bass or loudness of program. At lowest level of program material set "Maximum Line Adj." so that Main Dial Pointer reads the maximum number of lines at which it is desired to record. Rotation "Excursion Adj." counterclockwise will reduce the amount of excursion to minimum LPI required.
5. Tighten spring pressure nut ("A" figure 11, Instruction Manual, page 7, paragraph 20.)
SECTION II, VARIABLE FEED UNIT
Push the feed out, tighten the lock nut on top of the feed dial pointer, and set up the equipment as described in Section 1 of this bulletin. Place a disc on the turntable and set the lathe ready for automatic operation. Load a tape onto the tape machine, passing it through the advance head assembly and over the appropriate idlers for the speed of the disc, and by, reference to the chart enclosed, select the desired number of lines per inch and groove width, taking into account the playing time. As a rough guide, it is common to use 0.0025" for classical music, and somewhat more for "pop". For 45 rpm singles, groove widths as high as 0.004" may be used. As a safeguard, on the dial marked "Lines Per Inch", a second figure is given, indicating maximum groove width which may be permitted for a given number of lines per inch without overcutting in a dormant state, i.e., the groove width must not exceed 325 lines per inch when a groove width of 0.003" is set up on the cutter.
Take this as an example: Push the "Feed-In" button. The feed will, of course, commence as previously described in Section 1, but it will be noticed that the dial pointer will set itself at approximately 325 lines per inch. The field to the servo-motor is broken when the feed is "Out". In order to avoid possible damage to the idler on the mechanical part of the variable feed section in the "A" Base right-hand compartment, housed under the carriage, as mentioned on the warning plate in front of the feed pointer knob, the feed pointer should not be used when the feed is stationary, and similarly, an advance signal should not be allowed to activate it. Should this happen for an extended period, one is liable to wear a flat on the idler pulley in this system.
One word of caution: Should the motor be turned off with the feed engaged, and then restarted, the servo motor field will not be energized, as the supply is cut by a relay, although the feed will run mechanically. A flick of the "Feed-In" button will restore this relay, and the VFU to normal operation.
It is desirable that at the front of each tape a tone of approximately 250 cycles should be placed at zero level for about 15 seconds. The cutting channel and tape machine amplifier should be set to make this read zero. Similarily, the control on the VFU should be set so that its VU meter also reads "0", which will give the correct dynamic control to the system.
Depress the "Lead-In" button, and notice that during the run-in, the feed will expand to a predetermined amount. (See Adjustment Section). As before, the sequence of lowering the cutter, starting the tape machine and stopping the lead-in at the correct diameter will reoccur, and again the audio relay will be turned on. This time, however, the feed will hold expanded until after the audio light has been illuminated. This is done to avoid "pre-echo". Allow the tape to run, spiraling and finishing as before. A little practice will give the operator a knowledge of accurate settings required for tapes of varying dynamics and playing times.
In cutting long sides, the figures mentioned in the table should be rigidly adhered to. However, should a tape be cut with a groove width of 3 mils and it is required to space the grooves much farther apart than 325 lpi, due to short playing time, the VFU becomes more of a guardian device, and the land adjustment control should be rotated to give the number of lines per inch required. This causes the electronic unit to work as a gating circuit. Say the land control is adjusted to 200 lpi, any signal requiring less than that amount of expansion will not cause any change of the feed pointer; however, a signal calling for a feed coarser than 200 lines will cause it to act in the normal manner.
It should be noted that each time the spiral button is depressed, the feed will expand as before, and will hold expanded for a period determined by the setting on the clock on the sequence panel, again avoiding pre-echo of each selection of music. The finishing button will also expand the pitch.
MAINTENANCE & ADJ - FEED RANGE
Remove Allen cap screw holding idler gear bracket to inverted "L"-shaped bracket on Variable Feed Unit. An Allen wrench with an extension handle is supplied for this, and is inserted in a hole in the right end wall of the aluminum base to reach this screw. Remove idler gear bracket.
For 105 to 600 lpi gearing, remove "C" rings from idler gear shaft and position idler gear in center position. Insert a "C" ring on each side of the gear, and replace bracket in position in the variable feed unit, and adjust for nice running fit with two mating gears. Set dial at 142 lpi. Remove top clamping knob. Loosen Allen set screw on main dial knob, being careful not to rotate shaft. Remove main dial pointer knob. Remove two oval head screws and hex head screw with washer from dial plate. Remove 70 to 400 lpi dial, and replace with 105 to 600 dial. Replace dial pointer so that the pointer is at 216 lpi without rotating shaft. When fastening the dial knob, it will be necessary to push up on the textolite gear under the plate, as the shaft will drop slightly when the knob was removed. When the knob is fastened to the shaft, make sure there is a small amount of vertical play. Dial pointer should be set at 216 lpi when setting friction idler wheel parallel to base, as shown in Fig. 3.
For 140 to 800 lpi gearing, proceed as in the two preceding paragraphs, except that the idler gear should be placed in extreme right-hand position of idler shaft. Also, pointer should be set at 286 lpi when installing and setting dial pointer so that friction idler is parallel with base, as in Fig. 3.
If no servo unit is fitted, the hex head screw located just above the "Scully" on the feed dial plate is screwed into an eccentric stud underneath the dial plate. The stud should be adjusted so that the gear mounted on it is in nice mesh with its mating gear.
SECTION II-A - MAINTENANCE AND ADJUSTMENT OF VARIABLE FEED UNIT
Rotate the LPI switch to its fully counterclockwise position, ie. 600 lines per inch. By means of the feed pointer adjustment on the sequence panel, make sure that the dial pointer reads "600". Alter the lines per inch on the VFU, and return to "600", trimming the aforementioned adjustment as may be necessary. Make sure that the Land control is fully counter-clockwise, ie. in its inoperative (MIN.) position.
Turn the Lines Per Inch knob fully counterclockwise so that it reads "250 lpi". If the dial pointer does not read "250" within +- 10 lines, adjust the vernier potentiometer inside the VFU marked "250 LPI". Return to 600 lpi, and make sure that this setting has not changed, and go back to 250. Check the action of the lines-per-inch switch looking at the feed pointer and insure that it is operating as specified on the lines-per-inch dial of the VFU to be within +- 10 lpi. Should any trouble be encountered, check voltages as shown on the circuit diagram of this unit.
With the LPI dial set to 325, press and hold the spiral button and adjust the "Feed Expand" knob on the sequence panel so that the feed reads approximately 200 lpi. It will be noted that upon releasing the spiral button, a short period will elapse, and the audio relay will go on, indicated by the light on the pushbutton panel, and the feed pointer will return to the higher feed. This operation is achieved by the timing clock on the sequence panel, and should be adjusted in conjuction with the tape machine so that when the lead-in cycle is operating, the audio should come in approximately half a second before oxide reaches the playback head.
It is advisable to check the tubes in this unit once a year, or 2000 hours, and to replace them should their emission be outside manufacturers' specifications. Note: When changing components within this unit, it will be necessary to readjust the servo system, as previously described.
With an input to the VFU of +4 dbm, (1.23V at 250 cycles), set the LPI switch to read 325 lines. The feed should then expand to 280 lpi, and may be adjusted by means of the vernier gain control under the front panel. When this unit is fitted with an attenuator, it should be set at "14" and adjustments made by means of the vernier. With these parameters set up, ascertain that the VU meter on the front panel reads zero, and adjust this by means of the meter trimmer to be found under the front panel.
When this unit is used in conjunction with the variable depth unit, the cross feed adjustment should be set so that with the same input conditions as mentioned above, the feed will expand to 250 lpi.
In view of the RIAA characteristic inserted into this unit, it will be noted when sweeping the frequency spectrum that a greater expansion will take place for the lower frequency and lesser expansion for high frequency. The figures given are for cutting 6.2 cm/s at 1 Kc, and should your company standards dictate a different level, it will be necessary to increase or decrease the excursions accordingly.