The HAMMOND X-77 was one of the very first all solid-state models produced by the HAMMOND Organ Company. The technology was not very sophisticated, the transistor devices were primitive, and assembly methods and quality was not nearly as robust as the earlier "classic" B-3/C-3/A-100 organs�thus, the X-77 often suffered from hum, hiss, and audio "fireworks," among other problems.

There were three distinct production versions of the X-77: the "early" version, those instruments produced after July 1, 1969, and the "X-77GT" which also used the newer X-77P Leslie.

The X-77 Service Manual contains Field Service Notes for "correcting" some of the more noted "problems" with "early" organs manufactured before July 1, 1969:

• Percussion Keying by Pedal Solenoids
• Improvements for Pedal Response and Percussion Decay
• Adding Reverberation to the Percussion Signals
• Pedal "Pop"
• Hum Pick-Up in the Reverberation Unit
• Pedal Switch Assembly Problems, and
• Reduction of Hum and Noise

Reduction of Hum and Noise:

1. Modification of Bass and Percussion Preamplifier Board, P/N 124-000005:
   Remove transistors Q802, Q803, and Q805; replace with HAMMOND P/N 001-021070. The -070 transistor (2N3391A) was later superceded by P/N 001-021260 (2N5826), also a low noise type. HamTekker Wayne Johnson substituted NTE 199 transistors in his X-77.
   
2. Modification of Vibrato and Non-Vibrato Preamplifier Board P/N 124-000006:
   Remove two �W 120K Ohm fixed resistors, R405 and R442. Replace with �W 220K Ohm fixed resistors. Use carbon film type for lower noise.
   Remove two �W 1K Ohm fixed resistors, R420 and R456. Replace with �W 470 Ohm fixed resistors. Use carbon film type for lower noise.
   

Percussion Level and Cut-off Adjustments:

1. Connect meter to pin 9 and ground of the Bass and Percussion Preamplifier.
2. Depress upper manual B preset and SUPER QUINT and SECOND VOICE tabs.
3. Hold down upper manual key #30 and adjust R113 for a meter indication of 0.22V.
4. Connect meter to pin 4 of Bass and Percussion Amplifier. Output should be 0.4V when upper manual key #30 is depressed. If necessary, adjust R882, Percussion Level Control located on Bass and Percussion Amplifier board to obtain the correct reading.
5. Return SECOND VOICE tab to the up position. Hold down key #61 and if necessary, adjust R886 for an indication of 0.1V.

1. Connect meter to pin 8 and ground on Bass and Percussion Preamplifier.
2. Depress upper manual B preset and SECOND VOICE, XYLOPHONE,and REITERATION tabs.
3. Hold down key #48 on the upper ;manual and adjust Alternate Percussion level control, R313 for an indication of 0.40V.
4. Return SECOND VOICE tab to the up position.
5. Disconnect Plug P201 from the Percussion and Reiteration Driver. Hold down upper manual key #48, and adjust Alternate Percussion Cutoff control, R312 until output signal is barely audible.

1. Connect the meter to pin 4 of the Vibrato & Non-Vibrato Amplifier.
2. Depress the upper manual B preset.
3. Set the tone controls, R475 and R487 at their midpoint (or the desired position).
4. Hold down upper manual key #25 and Adjust R4833 to obtain a meter indication of 0.16V.

1. Connect the meter to pin 5 of the Vibrato & Non-Vibrato Amplifier.
2. Depress the upper manual B preset and ON UPPER tab.
3. Hold down upper manual key #25 and adjust R471 for a meter indication of 0.16V.

If all of the foregoing steps have been correctly performed, the outputs of the organ will be in accordance with the following table:

Output Pin	Output at Console Preamp	Output at Tone Cabinet Power Amp
Pin 4: Non-Vibrato	0.16 V RMS	2.2 V RMS
Pin 5: Vibrato	0.16 V RMS	2.2 V RMS
Pin 5: Bass	0.035 V RMS	0.27 V RMS
Pin 4: Percussion	0.4 V RMS	2.7 V RMS