HAMMOND ORGAN MODEL A
Wiring Errors OR Early Foldback Plan & a Mistake?
A few years ago, while checking the foldback plan in my model A # 728, I discovered what appeared to be "wiring errors" related to the 5th drawbar (3rd harmonic) and to the 6th drawbar (4th harmonic). Specifically, seven frequencies do not match the wiring plan published in the Hammond Technical Manual. These frequencies are marked in red in this pdf file.
Interestingly, by looking at the chart, the "erroneous frequency numbers" are the same frequency numbers of the 3rd drawbar (directly above and marked in pink). As you can see, the net result of this alleged wiring error is that the frequency components from the 6th drawbar in the top six notes are one octave lower that they should be. In addition, the frequency component from the 5th drawbar to the high C note is plain wrong.
This has been a mistery to me until now. This subject came up in a recent conversation with Michael Smokowicz. He recalls to have seen "wiring errors" in organs of the same vintage in the past . Today he was able to verify that # 957, which belongs to a friend, is also wired like mine.
Even though this wiring could be attributed to a manufacturing error, one could also theorize that it might have been an early foldback plan. Unless someone has specific knowledge, there is only one way to find out: check out as many of the early organs as possible.
So this can be a community project. If you have an early model A or model BC and are interested in this topic and also want to help solve this mistery, please check out your instrument and let me know what you find out. I will compile the data and publish it. Let me know if you need assistance with the procedure.
Bernardo Paratore
January 23, 2007
EASY TEST PROCEDURE
Because of the technical nature of this test and the desire of gathering as much data as possible, I have developed these instructions for conducting the test quickly even by individuals that are not familiar with the innards of a Hammond organ but would like to contribute to this project.
If you have a Hammond organ model A or a model BC with a serial number less than 1500, please perform the test explained below and let me know your results. This will take less than 5 minutes. No technical knowledge is required to conduct the test. Thanks!!!
There are two tests required and they can be performed either on the upper or lower manual. The procedure below describes use of the lower manual.
5TH DRAWBAR TEST
Refer to the picture below:
1. Push the B preset key of the lower manual.
2. Push all the corresponding drawbars in.
3. Pull out the 5th drawbar out to 8.
4. Play the high C key (blue)
5. Does it sound the same as the C key one octave below (green)? or
6. Does it sound the same as the F key two octaves below (red)?
6TH DRAWBAR TEST
Refer to the picture below:
1. Push the B preset key of the lower manual.
2. Push all the corresponding drawbars in.
3. Pull out the 6th drawbar out to 8.
4. Play the high G, G#, A, A#, B and C keys (blue)
5. Do they sounds like the corresponding keys one octave below (green)? OR
6. Do they sounds like the corresponding keys two octaves below (red)?
Email me your results:
Organ Model:_____________
Serial Number:____________
5th Drawbar Test Result (red/green):____________
6th Drawbar Test Result (red/green):____________
Your Name: (unless you want to remain anonymous)
I want to notified by email when this site is updated: (Y/N):_____