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Newer page: version 4 Last edited on January 23, 2011 2:04 pm. by 108.29.10.124
Older page: version 3 Last edited on December 28, 2009 9:02 am. by StefanVorkoetter
@@ -72,4 +72,91 @@
 It certainly puts new life into the old Hammond. 
  
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 I don't think the Goff capacitors are .224uF and .104uF respectively. "224" and "104" are the markings on the capacitors, but these are interpreted as 22x10<sup>4</sup>pF and 10x10<sup>4</sup>pF respectively. In other words, 0.22uF and 0.1uF. There are no such things as 0.224uF and 0.104uF capacitors. -- StefanVorkoetter 
+  
+------  
+!Capacitor Matching & R/C Filter Networks--Update on Tone Generator Capacitor Replacement--John Mihevic 01/23/2011  
+  
+First, thanks to Stephan Vorkoetter for noting that the correct values for the Goff capacitors is 0.22uF and 0.1uF  
+  
+The tone generator capacitor replacement I did in 2005 (described above) restores the tone generator performance to 90% of a new factory generator manufactured by Hammond in the '60s. To get the tone generator equivalent to Hammond's performance when new, I installed the R/C filter networks for frequencies 37 to 48 and individually matched capacitors to each filter coil for frequencies 49 to 91. Both of these improvements are described below.  
+  
+!Addition of R/C Networks  
+  
+I was not satisfied installing the Goff R/C filter networks for frequencies 37 to 48 without adjusting the coil magnet assembly for each frequency. The R/C networks load these frequencies resulting in a reduction in volume. The output was reduced by 1.5 mV - 2.0 mV RMS out of a nominal 4.5 mV, My solution was to measure the output of these frequencies before R/C installation, install the R/C networks, and adjust the coil magnet assembly closer to the tonewheel to increase the mV output of each coil to the values recorded prior to R/C installation. I am confident Hammond calibrated the tone generator with the R/C networks installed so the filter loading was part of the calibration.  
+  
+!Capacitor to Filter Coil Matching  
+  
+The capacitors in the Goff cap kit are matched in value to each other (0.22uF and 0.1uF). However, they are not matched to the filter coils as was done at the Hammond factory. The following paragraph is taken from a Hammond tech manual I have from the late 1960's with the requirement to match each coil/capacitor for frequencies 49 t0 51. This is in Section 5 (Main Generator), page 3 of the manual.  
+  
+ ''Two condenser values are used - 0.255 mfd for frequencies 49 to 54, and 0.105 mfd for frequencies 55 to 91. The transformers are all different. Each transformer is matched to its condenser and any replacements are supplied as matched pairs by the factory. ''  
+  
+For me to accomplish this resonant frequency matching, I purchased +/-10% Sprague Orange drop series 225P capacitors from Newark Electronics. It was the +/-10% tolerance that allowed me to match each capacitor to each filter coil. The values I used were .22uF(220nF) .082uF(82nF) .015uF(15nF) .01uF(10nF) .0047uF(4.7nF) .0033mF(3.3nF). Note that 1000nF = 1uF  
+The actual range of measured values were:  
+  
+<verbatim>  
+ Marked Value Actual Range In Value  
+  
+ 220.0nF 230.0nF – 241.0nF  
+ 82.0nF 83.2nF - 91.4nF  
+ 15.0nF 15.40nF  
+ 10.0nF 9.50nF – 10.18nF  
+ 4.7nF 4.86nF – 05.21nF  
+ 3.3nF 3.60nF  
+</verbatim>  
+  
+In many cases I used two capacitors in parallel to get the correct value. The final value of capacitance was obtained by increasing the value of capacitance until the maximum mV output was obtained. More or less capacitance reduced the mV output. The model of a real capacitor includes a resistive and an inductive component. The magnetic pickup has resistance and inductance. All of these, and some components that I don’t even know about, affect the resonant frequency which is the desired output of a given tonewheel. The equivalent circuit/math model is complex. With my method, tuning is done with the actual capacitor(s) that will be soldered to the filter coil. Every circuit component is included in the capacitor/coil matching. In this way a tuned circuit resonant peak is obtained at each tonewheel frequency with optimum filtering of unwanted frequencies and the signal to noise ratio is a maximum for that frequency. I should mention that I still have enough “crosstalk” that is part of the classic Hammond sound. All work was done with both manuals raised and the tone generator in full operation. Access to the tone generator was from the front of the organ. The table below has the final value of capacitance that resulted in the maximum mV output for each frequency from 49-91. Column 1 is the “Frequency No.” Column 2 is “Capacitor(s) Used”. Column 3 is the “Total Capacitance” value. Column 4 is the value of the “Goff Cap Removed”. Column 5 is the value of “Wax Cap” that was originally installed by Hammond.  
+  
+<verbatim>  
+Freq Capacitor(s) Total Goff Cap Original  
+No. Used Cap Removed Wax Cap  
+ nF nF nF nF  
+  
+49 241.0 - 241.0 225.0 580  
+50 233.0 - 233.0 225.0 412  
+51 230.0 - 230.0 226.0 400  
+52 230.0 9.90 239.9 226.0 485  
+53 237.0 3.60 240.6 227.0 590  
+54 236.0 4.86 240.9 228.0 360  
+55 83.6 4.99 88.6 99.6 203  
+56 86.2 4.93 91.1 99.9 330  
+57 86.4 4.95 91.4 99.3 183  
+58 88.2 5.21 93.4 98.6 340  
+59 87.1 4.88 92.0 100.0 320  
+60 91.4 - 91.4 100.0 350  
+61 88.3 - 88.3 99.9 280  
+62 89.3 - 89.3 100.0 330  
+63 86.9 4.88 91.8 99.9 188  
+64 85.6 4.95 90.6 100.3 410  
+65 88.0 4.86 92.9 100.9 365  
+66 88.0 3.60 91.6 102.0 260  
+67 83.2 5.13 88.3 100.5 350  
+68 87.6 4.94 92.5 101.2 290  
+69 85.6 9.83 95.4 100.8 238  
+70 88.6 9.68 98.3 100.5 320  
+71 87.7 10.03 97.7 101.5 400  
+72 85.9 5.00 90.9 102.0 320  
+73 88.6 - 88.6 102.2 340  
+74 85.2 4.98 90.2 101.8 215  
+75 90.2 - 90.2 101.9 360  
+76 87.3 5.00 92.3 102.1 270  
+77 90.2 - 90.2 101.8 223  
+78 85.6 9.85 95.5 101.8 330  
+79 87.5 9.50 97.0 102.3 215  
+80 84.8 9.57 94.4 101.6 315  
+81 88.1 9.78 97.9 103.5 300  
+82 84.8 15.40 100.2 103.5 211  
+83 86.7 9.83 96.5 102.5 410  
+84 87.8 9.69 97.5 103.5 330  
+85 86.4 9.76 96.2 102.5 165  
+86 87.9 9.50 97.4 102.5 322  
+87 88.9 9.76 98.7 103.6 410  
+88 85.9 10.18 96.1 103.0 184  
+89 85.2 9.56 94.8 103.4 540  
+90 87.9 4.96 92.9 104.2 380  
+91 88.0 4.98 93.0 105.6 250  
+</verbatim>  
+  
+At every frequency, the capacitor to coil matching produced a higher millivolt output than with the Goff capacitors that I replaced. The highest change was +1.72 mV. The drawbar definition is increased with more crispness, clarity and presence of the organ tone/timbre. Capacitor/coil matching is not for everyone (it is time consuming), but if you are so inclined, the reward of restoration, identical to what came out of the Hammond factory, is well worth it.  
+  
+!—John Mihevic  

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