Generator pickups 44-48

[dunderola]

Ok. So here is another twg related question. Model A 1936. Pictured is tone nr 47. Same thing on tone 44-48, in schematic only have a coil, no cap or no resistorwire. 2nd pic is "normal". 1st is the coil bypassed and coil output direct to oscilloscope. What causes this ugly curve on 2nd and what use of the filter when disconnected makes a much better wave, of course with stronger output? could back the magnet to take it down though..

[David Anderson]

To my eye, it looks like the tone is being modulated by another (higher) frequency. Perhaps the coil is acting as a pickup for a higher frequency. That said, I've never seen that kind of waveform modulation from 44-48 on other organs.

Try turning on the organ without starting the generator and see if that modulation frequency is still there.

[enor]

I bet the coils are microphonic due to delamination. Tap them with a pencil and see if you get a signal! Or indeed, tap anywhere on the generator chassis (that was enough to disturb the output when I was facing this problem).

[Drawbar Dave]

In this sort of instance can a coil from a spinet generator be used on a prewar console? Are they the same?

[enor]

In this sort of instance can a coil from a spinet generator be used on a prewar console? Are they the same?

They work (I replaced the faulty ones on my generator with filters from an M-100 generator) but they don't quite fit as-is. The mounting holes are different so it's only possible to use one screw; and the terminals are wired differently so you need to either splice your cables or reroute the wiring on the spinet filter slightly.

[kziss]

Ok. So here is another twg related question. Model A 1936. Pictured is tone nr 47. Same thing on tone 44-48, in schematic only have a coil, no cap or no resistorwire. 2nd pic is "normal". 1st is the coil bypassed and coil output direct to oscilloscope. What causes this ugly curve on 2nd and what use of the filter when disconnected makes a much better wave, of course with stronger output? could back the magnet to take it down though..

Hi Dunderola.
On the Hammond organs built from the 1930's up to 1964 there were the transformer only filter coils on the TG notes 44 to 48, but in 1964 Hammond changed this set up by introducing the 47 uf / 10 ohms RC hum filters on the TG notes 37 to 48.

On pre 1964 organs with the transformer only filters on the TG notes 44 to 48, there is a subtle faintly audible higher frequency leakage note audible above the sine wave TG notes 44 to 48 so therefore I suspect that this higher frequency leakage might possibly be contributing to the particular waveform shape in your photo.

The transformer filters on the TG notes 44 to 48 acted as high pass filters to remove a low frequency tonewheel leakage undertone and a hum noise which is audible underneath the direct unfiltered TG notes 44 to 48.
There was also some leakage undertone and hum present underneath the unfiltered TG notes 37 to 43 of the pre 1964 organs, and Hammond dealt with this with the RC hum filters which were introduced on all the TG notes 37 to 48 in 1964 and these RC hum filters were used until the end of production in 1975.

On my own organs I have completely bypassed the TG note 37 to 48 RC hum filters, and I then recalibrated the TG note 37 to 48 pickup magnet rods in order to bring down the now unfiltered and noticeably louder TG notes 37 to 48 back to their original output levels.

The reason why I completely bypassed the TG note 37 to 48 RC hum filters is because to some degree they thin out the tonality of the TG note 37 to 48 sine waves, so therefore fully bypassing the RC filters causes the TG notes 37 to 43 to sound fatter like that on the pre 1964 organs, and the raw unfiltered TG notes 44 to 48 also sound fatter .

I can hear the low frequency undertones and a slight hum underneath the unfiltered TG notes 37 to 48, but I am not bothered by this, however some people might find the slight background hum noise objectionable.

could back the magnet to take it down though..

Yes you can.
If you prefer the fatter sound of the TG note 47 with the transformer filter bypassed, then you can completely bypass the transformer filters of the TG notes 44 to 48 and then restore the original output levels of the TG notes 44 to 48 by pulling out the corresponding TG note 44 to 48 pickup magnet rods.
All the best.
Kon.

[dunderola]

Thank you very much for this, Kon.

[dunderola]

Any need for resistor wires on these notes like on 1-43? Well, or more like a wire with an attached resistor due to lack of odd wires in my stash...

[enor]

Also worth noting: The polepiece locking screws on these old generators are EXTREMELY fragile. I broke a couple on my generator and had to calibrate those frequencies by deliberately mis-tuning the filters for those frequencies.

[dunderola]

Also worth noting: The polepiece locking screws on these old generators are EXTREMELY fragile. I broke a couple on my generator and had to calibrate those frequencies by deliberately mis-tuning the filters for those frequencies.

Yes i know exactly what you mean. Although ive been doin tough fasteners for a looong time now. But, just lubing the clamp and before that using brake cleaner loosen up most of them. Infact loosen them to the amount that adjusting can be done with a firm grip with a polygrip without loosening the screw. Not recomended but once the screw breaks its a bit tricky to remove them at all. Some say dont twist the magnet rod, but it can be wiggled some degrees if done with a bit of touch :)

[kziss]

Any need for resistor wires on these notes like on 1-43?

Hi Dunderola.
Years ago I recall reading somewhere that the grounding resistance wires for the pickups of the TG notes 1 to 43 are approximately 16 ohms, however I have not been able to verify the actual resistance wire values because the grounding resistance wires are in parallel with the pickup coil wires so therefore the total measured resistance of a pickup is the parallel resistance of the coil wire and the grounding resistance wire.

As I recall, after I fully bypassed the RC hum filters from the TG notes 37 to 48, I then experimented by re-setting one of these raw unfiltered TG notes to it's normal original mVpp output level, and I then pressed a corresponding keyboard key in the fourth octave of the keyboard ( which contain the TG notes 37 to 48 on the 16 ft drawbar keycontacts ) in order to see how much the mVpp output level of that particular TG note was reduced because of the loading effect created by the pressed key, and after this I recall temporarily wiring up a 16 ohms grounding resistor to the output wire of that TG note, and with the 16 ohms grounding resistor in place, I then re-set that TG note to produce the normal original output mVpp output level, and I then pressed down the same corresponding keyboard key, and I then noticed that the mVpp output level of that TG note had reduced to a similar level as what it did when I tested it the first time around without 16 ohms grounding resistor.

After doing this experiment, I then disconnected the 16 ohms grounding resistor and I then reset that TG note back to it's original mVpp output level.

Because of the similar result in both tests in this experiment (first without the 16 ohms grounding resistor and then with the 16 ohms grounding resistor in place), I concluded that there is no real need to wire up grounding resistors in parallel with the raw unfiltered TG notes 37 to 48 because the keyboard induced loading effect basically remained the same.

I am not sure how much the transformer filters of the TG notes 44 to 48 in the pre 1964 organs affect the loading down characteristics of the TG notes 44 to 48 when the keys are pressed, but you can experiment to find this out by taking note of the normal original mVpp or the mV RMS output levels of the TG notes 44 to 48 as they are with the stock transformer filters in place, and then press down the corresponding keyboard keys 44 to 48 on the fourth octave of the keyboard that contain the TG notes 44 to 48, and then write down the resulting reduced mVpp or mV RMS output levels.

After this you can then completely bypass the transformer filters of the TG notes 44 to 48 and then reset the TG note 44 to 48 pickups to produce the original mVpp or mV RMS output levels, and then redo the test by pressing down the keyboard keys 44 to 48 and then write down the resulting reduced mVpp or mV RMS output levels.

If the resulting reduced mVpp or mV RMS levels of the TG notes 44 to 48 are similar both with the transformer filters in place and then without the transformer filters, then you do not need to worry about wiring up grounding resistors in parallel with the raw unfiltered TG notes 44 to 48.

However if there is a noticeable difference in the resulting reduced mVpp or mV RMS output levels of the TG notes 44 to 48 and if you then decide that you want the raw unfiltered TG notes 44 to 48 to produce similar loading down characteristics when the keys are pressed as what they did when the stock transformer filters were in place, then you can experiment by wiring up different grounding resistors until you find a resistor value which produces a similar reduction in the loaded down mVpp levels as that produced by the stock filter transformers.

Well, or more like a wire with an attached resistor due to lack of odd wires in my stash...

Yes a resistor can be used as a direct substitute for resistance wire.

All the best.
Kon.

[Frankquip]

Put a 33 uf cap in parallel with the pickup coils 44 -48 going to the transformer filter - you will notice an increase in signal, then you can adjust the pickup to compensate. the keyboard loading will not be affected and the signal will be much cleaner.

[dunderola]

Unfortunately i already bypassed the filters causing the signal much higher. When backing of the rods the signal went a bit uglier. Then i put resistors to ground as in 1-43 and moved the rods in a bit again. Looks much better now. More like 1-43ish. Not perfect but ok.

[dunderola]

And thank you all for every input i got in this thread. Much appreciated.