The V301H "California" Continental Tone Generator Repair






If your V301H Vox "American" Continental is missing tones, chances are you have a problem with one of the six divider circuits found on each tone generator card. This web page is designed to help you diagnose, and possibly even repair this V301H Continental problem on our own.

The Vox Showroom and North Coast Music accepts no reposnsibility for personal injury or damage to property while using this information to attempt an organ repair. Proceed at your own risk.

First, turn on the organ, connect to an amplifier and pull out only the 16' and ~ drawbars. All other drawbars should be pushed fully in. Starting with the low C, which is called "C1", test each note from the lowest to the highest key of the organ, which is called "C5". Listen for any note that seems to be an octave or more higher than adjacent notes. This symptom points to a problem in the divider circuitry.

Should you find a key that has a tone one or two octaves higher than expected, you should check the higher octaves of that note as well. As the dividers are wired in a serial fashion (one feeds the next), a divider failure will also affect the tones of all the dividers after it. As an example, if the second divider is malfunctioning, and not dropping it's tone by an octave, the output of the third through sixth dividers will also be off by one octave.

Here is an hypothetical example of a typical divider problem. When testing the organ, you find that the frequency of the "B2" tone is the same as the "B3" key. This points to a defective divider on the "B" tone generator card.

An oscillocope is helpful, but not necessary, to diagnose a defective divider. Start by locating the "B" tone generator card in the organ. The B tone generator card can be identified by the letter "B" stamped on the tuning coil (see photo, lower at left). This card will have the defective divider. Assuming you have an oscilloscope, prepare to start the diagnosis of the problem by attaching the ground lead of the scope to the organ chassis.

Starting with the socket for the 1st divider (see bottom of photo at left) probe each of the dividers with the oscilloscope. The 1st divider will have the highest pitch or frequency. As you move through the dividers from one to six, you should observe a one octave drop from one divider to the next. In other words, the output of the 6th divider should be five octaves lower than the output of the first divider.

Using the "B2" and "B3" example above, it would be likely that you would not observe an octave drop between the the 4th and 5th divider. It is likely that the transistors may be bad on the 4th divider. While it is somehat possible that there is a bad capacitor or resistor in the divider circuit, it is more likely that the transistors may be bad on the 4th divider. Replace both transistors on the 4th divider, referencing to the drawing at at left, and recheck the organ. If it still doesn't work properly, you may also need to change the transistors on the 5th divider.

What transistor do you need? The orange dotted transistor is a 2N2923, and the yellow dot transistor is a 2N2924. You may replace either with an NTE85 transistor, available for about $1 each from such suppliers as www.mouser.com or www.newark.com.

Transistors have three leads - base, emitter, and collector. When replacing, these must be installed in the correct order. You might want to purchase the recent North Coast Music remastering of the Vox V301H schematic to help you, click here to purchase this from North Coast Music.

If you don't have an oscilloscope, no problem. Click the "Jump" button at the bottom of the page to view the next page, which offers a way to diagnose a tone generator divider problem without test equipment.


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


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