Help with filter coils on Hammond generator, gone open

[Dave S.]

Hello people, this is my first post. I recently acquired an old Hammond M to use in a little band i'm playing in. Hoping someone can give some insight on these filter coils atop the generator. Three ofthem are reading very high and/or open, resulting in annoying dead notes on 49, 56 and 63. Didn't find any fractured windings, so I guess their time is up. When Iworked for a Hammond retailer here in FL, we'd justinstall some working replacement coils of a matching numberfrom a parts generator and call it a day. Now that I don't have that luxury, I need to find out if anyone's used conventional resistors to fix this ailment sucessfully; also if anyone knows if those coils had a resistance common to the note they were assigned, I never did measure between twogenerators to see if there was any similarities. Unfortunately I never did own any tech manuals that would have had this info, the ones I had were shop property. Can anyone help, or point me in the right direction? Thanks in advance</P>


Dave</P>

[geoelectro]

Re: Help with filter coils on Hammond generator, gone open



The problem with using a resistor or even connecting the pick-up coil direct is the additional signals from crosstalk. (Two tone-wheels per compartment) </p>

The filter cuts out the additional signals AND peaks the wanted signal. I have bypassed the filter coil before and usually the signal is weak and full of unwanted crosstalk.</p>

George
</p>

[Dave S.]

Re: Help with filter coils on Hammond generator, gone open

Yeah, that's pretty much what happened when I tried it,I thought I may have been missing something. I guess i'll have to go hunting for these things, I doubt even the local electronicmilitarysurplus store has anything remotely close to them.

[fredy2]

Re: Help with filter coils on Hammond generator, gone open



Can you rewind them? Often coils break very near the connections and can be repaired... If they are potted, sometimes the potting can be removed... </P>
<P mce_keep="true"></P>

[Tinker]

Re: Help with filter coils on Hammond generator, gone open



That's a great suggestion Fred. I've repaired a number of vintage relays with an unwind and rewind process, usually just reterminating the same wire eliminating the end break. All the ones I've repaired so far have been at one end or another of the winding. I've made up a spool gadget and various relay coil holding rotating shafts so with the help of a variable speed drill and a little dexterity it makes the process pretty painless. Lots of turns in a lot of those and while I'm patient enough to repair them I'm not sure I'm crazy enough to unwind and rewind them by hand ;^)</p>

</p>

[fredy2]

Re: Help with filter coils on Hammond generator, gone open



I bought one of the coil winder things from China that has a counter... I think I got it on Ebay... Haven't used it yet, but I have a couple transformers to rewind... 1000 volt one for a scope... </P>


Key is to find right sized wire... ALSO try to measure the inductance or find what it is supposed to be and wind too much and then tune it...</P>


I bet your coil has the break at the end... probably draawn too tight to the terminal and vibration broke it... Use a toothpick to gently move wire near the terminal... ALSO have seen bad solder at the terminals... Might try re-heating as first step...</P>

[Dave S.]

Re: Help with filter coils on Hammond generator, gone open

On two of these I checked the endswhere they come off the winding and solder to the terminals, they're solid, also reflowed the solder joints. No change. The third one did have a fracture at one end, but after removing it and staring at it for about 30 minutes under the magnifying light I sure couldn't find the other side of the broken wire. I may just try unwinding this one, guess at this point I couldn't hurt it much more.Couldn't be much worse than tracing down broken nylese wires in the manuals......(shudders, then knocks on wood)

[fredy2]

Re: Help with filter coils on Hammond generator, gone open



I assume all of these show open circuit with the ohmmeter...</P>


I have often thought about connecting an ignition coil up to cause a spark between the open ends... and observe in a darkened room...</P>


Just had a fantastic idea! One of those piezo spark igniters for grills to do the same!!!! </P>


Here is another idea for non-destructive testing... Use a capacitance meter to measure between core to get an idea of the percentage of area of the two broken parts... Even more sophisticated is TDR (time domeain reflectometry)...</P>

[Dave S.]

Re: Help with filter coils on Hammond generator, gone open

[quote user="fredy2"]


I assume all of these show open circuit with the ohmmeter...</P>


[/quote]</P>


Yeah, two are open, one shows something absurd like 27meg.</P>


[quote user="fredy2"]</P>


I have often thought about connecting an ignition coil up to cause a spark between the open ends... and observe in a darkened room...</P>


Just had a fantastic idea! One of those piezo spark igniters for grills to do the same!!!! </P>


[/quote]</P>


Cool idea!! I've got an old grill lighter laying around somewhere, i'm gonna try that sometime. I did finally manage to stop in at my old workandscored three coils. They're the wrongnote numbersoff a 70's era generator anddon't quite put the notevolumein the range where it's even with the others, but it's a suttle imbalance, probably won't even notice once it's all in the mix. I will try that grill lighter thing and see if I can get the original coils fixed though. Thanks for the idea!</P>