Hammond Instrument Co. SOLVOX Schematic

Hammond Instrument Co. SOLVOX

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Manufacturer:Hammond Instrument Co.

Schematics Content

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Tell the customer "No" who asks you to extend the three cables connecting keyboard to tone cabinet. Extension cables are not available from tbe factory.

We definitely advise against splicing on longer wires. Critical tuning circuits are completed by some of these vires and a change in length may upset note-to-note tuning.

If it is desirable to move tone source farther from the keyboard than cables from tone cabinet permit, remove the loud speaker and extend its rires. Five wires are required. Make connections as shown in sketch. Be sure to mount the speaker in a balne approximately size of Solovox case,

TUBE REPLACEMENTS Solovox tubes are excluded from 1 year guarantee which goes with each instrument. Tube manufacturers regular guarantee appliance. Tubes may be return ed for replacement thru jobber Or to us.

free replacements are allowed only if tube are not broken or damaged, act. ually test bad, and code marking shows them in guarantee. Obsolescence schedule is shown here for your guidance. Tubes with code dates other than those shown are obsolete and not subject to adjustment.

ADJUSTMENT OF OSCILLATORS The service man should have a thorough knowledge of oscillator adjustment because he will most likely be called upon to perform this service more frequently than any other. A change in setting of the master tuning knob, a change of keyboards or installation of a new oscillator tube will necessitate readjustment of the oscillators. It is often advisable for the service Ban to give instructions on 080illator adjustment to the Solo VOX owner. The following is a detailed explanation of oscil 1 & tor adjustment.

The master oscillator is tuned by the condensers in the key board and supplies frequencies for the highest octave of the six octave tonal range. The buffer oscillator, which is con bidered as a controlled oscillator although it has no adjustment potentiometer, is used as an electron io link between the master oscillator and the rest of the controlled oscillator and has its circuit constante pre determined so 28. to oscillate at the same frequency the master oscillator, Each of the remaining controlled oscillators when supplied with the proper amount of locking signal should oscillate at one half the frequency of the preceding oscillator. This looking signal is the same signal that is generated by the preceding oscillator but the amplitude is regulated by the adjustment potentiometer and then impressed upon the grid of the following oscillator tube.

CORRECT SETTING OF POTENTIOMETER ARM NOTE Position of slot shown here does not necessarily mean that every slot will assume this position when correctly adjusted.

Assuming that the master and preceding oscillator are operating correctly, the following is an explanation of what happens in a complete rotation of an adjustment potentiometer. See figure # I. Turning the potentiometer to its extreme counter clockwise position the oscillator - 111 operate at the same frequency as the preceding Oscillator because the amplitude of the locking signal is too great. Now, turning the potentiometer clockwise, a point is reached where the oscillator 100k8-1n at one-half the frequency of the preceding oscillator because the amplitude of the locking signal is of proper intensity to pause this condition. It is then operating exactly one octave below the preceding oscillator and for correct adjustment the potentiometer arm should be set id way between the top and bottom lizita of thi. 1/2 frequency range. Turning the potentiometer further clockwise, a point * 111 be reached where it vill either look-in at one-third the frequency (this is an octave and a fifth below musically speaking) or, it may refuse to look-in and will start to hunt a frequency of its own which boars no definite mathematic relation to the frequency of the preceding oscillator. A gurgle is usually present at the point where the oscillator starts to change to a different frequency. Conditions that may make oscillator adjustment difficult or impossible are the following:

1. Improper operating voltages at the grid, plate or cathode of an oscillator tube.
2. Defective oscillator tube.
3. Inoperative master or buffer oscillator,
4. Defective parts associated with the oscillator circuits.

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PROCEDURE FOR ADJUSTMENT OF OSCILLATORS. The primary requisite for adjusting oscillators are that the master and butter are operating correctly and that you must atart by adjusting the 2nd 08011lator and then progressively adjust each succeeding 08011 later. After you have become familiar with the method of adjustment as described in " To The Solovox Owner you may try the following method which is somewhat quicker. Push "on" the Soprano " only, and adjust the 2nd and 3rd oscillator by depressing r key in the middle and lowest octave respectively. Than, vui Hon the " B8.88 " only and adjust the 4th, 5th and 6th oscillator by decreasing F key in the highest, middle and lower octavo You may cheek adjustment of the six octave tonal range by running down the with the " Soprano * only non and then with the " Bags only on ". OF COVI RC, in this cheek the low key with the Soprano on * should be chromatically related to the high B key with the " Bas8 " on. " It the adjustment potentiometers should get so far out of adjust mont that you besona contund, the following hint may prove help Iul, Turn all potentiometer.'to their extreme counter clockwise positions and then follow the normal oscillator adjustment procedure


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SPECIAL SOLOVOX SERVICE NOTES TROUBLE: - Difficult or impossible to adjust oscillators
some tones " gargle or play wrong notes.
A survey in the field shows that so % of all the Solovox service problems are confined to trouble experienced with a single fixed carbon resistor of critical value which makes it impossible to properly adjust the oscillators and causes the tones to " gargle " or play wrong notes when this resistor changes in value due to dampness.

This resistor is of the fixed carbon type having a value of 200,000 ohms (250,000 ohms for some models) and is connected in the voltage divider circuit for the bias on the controlled oscillators (shown at the upper left in the figure 1 wiring diagram supplied with each instrument). The physical location of this resistor in the Solovox tone cabinet is shown on the reverse side of this sheet. If the tonos or play wrong notes, connect a DC meter across the 8000 ohm wire wound resistor also shown on the reverse side of this sheet using a 1000 ohms per volt meter on the in volt scale. The meter should read approximately 2 volts with no keys depressed, and smoothly drops to zero and then to a alightly positive voltage as the top seven white keys are progressively played starting from the top key (key farthest to the right), If this voltage is low, remove the resistor and replace with a new one (such as an I.R.C. metallized resistor or Centralab resistor). If possible, use a 2 watt res19tor as they are more stable than the 1 watt size. After replacing this resistor, be sure to readjust the oscillators as described on page 2 in " To Solovox Owners. "


Volume low Ten percent of all Solovox service trouble lies with another fixed carbon resistor which increases in.resistance due to humidity and thereby causes the maximum volume attainable to go down This register is also of the fixed carbon type, having & value of 330,000 ohms (370,000 ohms in some models) and is connected in the volume control voltage divider circuit shown at the lower right in the figure 1 wiring diagram. The physical location of this resistor is also shown on the reverse side of this sheet. If the volume is low even when the " maximum value control " is turned for maximum volume, remove it and replace with a new 300,000 or 250,000 ohm resistor (such ag an I.R.C. metallized resistor or Centralab resistor). If possible, use a 2 watt resistor as they are more stable than the 1 watt. size.