Factory Field Changes to the X-77 Organ
1 von 3
https://web.archive.org/web/20110915000118/http://www.myplanet.net...
The Wayback Machine - https://web.archive.org/web/20110915000118/http://www.myplanet.net:80/x77dude/x77…
"Improving" the X-77
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
We will focus our attention on the latter issue; X-77 Owners who are experiencing one of the other listed
problems are invited to e-mail me to obtain the appropriate Service Note.
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transistor (2N3391A) was later superceded by P/N 001-021260 (2N5826), also a low noise type.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 ½W 120K Ohm fixed resistors, R405 and R442. Replace with ½W 220K Ohm fixed
resistors. Use carbon film type for lower noise.
Remove two ½W 1K Ohm fixed resistors, R420 and R456. Replace with ½W 470 Ohm fixed resistors.
Use carbon film type for lower noise.
These changes improve the signal-to-noise ratio of the affected circuits by increasing the gain of certain
stages—thus, adjustments of the outputs is required to restore the proper levels in the Vibrato and NonVibrato preamps, as well as the Percussion Level and Cut-off and Alternate Percussion Level and Cut-off.
Use a Digital Voltmeter or AC VTVM to make the following measurements. Set the Swell Pedal for full
output.
Percussion Level and Cut-off Adjustments:
23.11.2022, 20:02