Fuzzy Sound

[Guest]

Hi All, this is my first post.</p>

I have a 1938 Hammond BC with a Leslie 122. I got it a little over a year ago, and it was non-functional when I got it. I tested the tubes, and one of the main output tubes on the leslie was dead, so I replaced that one. It has worked since then, although it has a slight problem that went away for about a year now, but it has recently started doing it again. I fire it up, and start playing. Within about 5 minutes, the sound gets quiet, and very distorted. I can make it only about 1 song before it quits. I tested all the tubes a little over a year ago, and replaced the one bad one, and it did the same thing then. I wish I could afford the time and money to completely overhaul the entire rig, but I just want to locate the one problem for now. Is it in the leslie or the organ preamp? Any ideas about where to start? I plan on restoring the organ as much as I can over the next few years. It has lots of miles on the woodwork, so I need to do some repairs there. I also plan on replacing the caps in the leslie amp and crossover somewhere down the road. I just want to take care of it as much as possible, and I have little experience with tube amps. Any suggestions would be welcome.</p>

Thanks </p>

[tonewheel1966]

Re: Fuzzy Sound



You say you replaced main output tube replaced on the Leslie. If this is one of the two 6550s (biggest ones) they should be replaced as a pair as the balanced output from the organ works in a push/pull manner. It seems strange that the problem takes five minutes to manifest itself as the tubes should be warmed up in 30 seconds.</P>
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Have a look at the service info page on Benton Electronics for the Leslie amp. I have found this site and the owner very helpful</P>


Cheers</P>


Dave</P>
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[Tim Rinkerman]

Re: Fuzzy Sound

I'll be following this thread as well...since I put an Organmate reverb in my C-3, it will quite often, play fine for about ten minutes, then get very quiet and dirty, and most often, will go back to normal after about ten more minutes. I suspect the reverb, but, I'm curious to see what others say...

[tonewheel1966]

Re: Fuzzy Sound



Tim does the organmate reverb connect into the AO28 via a valve socket as per the trekII version that I am considering? If so check the socket is clean for starters. Failing that it is the elimination game. Remove the reverb kit for a bit and see if the problem continues. Let me know the spec od your reverb though because I want to buy one for my RT3</P>


Cheers</P>


Dave</P>

[Tim Rinkerman]

Re: Fuzzy Sound



Dave..thanks for the thoughts...I connected it by detouring the connection between the tube socket and the tone pot through RCA in/out jacks as per the organmate instructions. It gets power from the switched mains lugs on the pre amp. If you have the chance to get one, do it by all means. I wasvery impressed by how good it actually sounds.It doesn't sound "added on", it feels like you are in a big room.</P>


Yes,if I bypass the reverb the signal is fine...when I re-insert it, it always goes back to fine, like there was never anything wrong..until the next time I start it. It's in the reverb, but it has proven impossible to get to it in the failed mode, it always corrects itself by the time I get a meter and probes to it. It must be a component that has changed value, or is failing, but I'm not circuit savvy enough to go after specific parts. It will gradually decrease in volume and increase in "dirt" over about 30-45 seconds of playing when it does it. It stops at about a 60% reduction in volume, and the notes are completely"fuzzed" out. Sometimes it will come back up after about 5 minutes if I don't touch it, other times it will come back only if Iturn the organ off and then restart it.The thing that interests me about this problem, is that if I can identify where this problem is occouring, and put a knob there, I could fulfill everybody's dream about having any degree of genuine tube driven distortion at a comfortable volume. There is about a 15 second time spanon its way down, that the quality of the distortion is truly remarkable. When it's fine, it's perfect..not a trace of distortion.It doesn't produce any bad noises like clicks,pops, or hissing to lead you to suspect any particular part. Tim</P>

[geoelectro]

Re: Fuzzy Sound

[quote user="tonewheel1966"]

You say you replaced main output tube replaced on the Leslie. If this is one of the two 6550s (biggest ones) they should be replaced as a pair as the balanced output from the organ works in a push/pull manner. It seems strange that the problem takes five minutes to manifest itself as the tubes should be warmed up in 30 seconds.</p>
<p mce_keep="true"></p>


Have a look at the service info page on Benton Electronics for the Leslie amp. I have found this site and the owner very helpful</p>


Cheers</p>


Dave</p>
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[/quote]</p>

The output tubes in a Leslie amp are normally quite stressed. A bad 6550 can "go thermal" by over conducting to the point of causing the plate to glow red. (Normally black) This can be observed with the naked eye. This "going thermal" can take a few minutes or an hour. It depends on the tubes condition. You can measure the input grid voltage and likely see it rise very quickly. (should stay below 1Vdc)</p>

While I'm on this subject, the coupling and feedback caps in these amps should all be replaced. They can leak small amounts of DC that will cause the outputs to over conduct just like they were bad. In fact, bad coupling and feedback caps can damage your outputs.</p>

George
</p>

[TheAdmiral]

Re: Fuzzy Sound

You have a 70 year old organ. The capacitors' life is usually last about 15 years max. The first thing you should do is replace every capacitor in the organ preamp as the old wax ones do worse than all the others. That includes the can capacitors (they can be replaced with tubular or axials). It's a small preamp with only a few so no big deal. Actually all of them on the generators should be replaced too but that is a big deal. Start small and see a big improvement. The preamp suffers heat damage in addition to age.

[tonewheel1966]

Re: Fuzzy Sound

[quote user="Tim Rinkerman"]


Dave..thanks for the thoughts...I connected it by detouring the connection between the tube socket and the tone pot through RCA in/out jacks as per the organmate instructions. It gets power from the switched mains lugs on the pre amp. If you have the chance to get one, do it by all means. I wasvery impressed by how good it actually sounds.It doesn't sound "added on", it feels like you are in a big room.</P>


Yes,if I bypass the reverb the signal is fine...when I re-insert it, it always goes back to fine, like there was never anything wrong..until the next time I start it. It's in the reverb, but it has proven impossible to get to it in the failed mode, it always corrects itself by the time I get a meter and probes to it. It must be a component that has changed value, or is failing, but I'm not circuit savvy enough to go after specific parts. It will gradually decrease in volume and increase in "dirt" over about 30-45 seconds of playing when it does it. It stops at about a 60% reduction in volume, and the notes are completely"fuzzed" out. Sometimes it will come back up after about 5 minutes if I don't touch it, other times it will come back only if Iturn the organ off and then restart it.The thing that interests me about this problem, is that if I can identify where this problem is occouring, and put a knob there, I could fulfill everybody's dream about having any degree of genuine tube driven distortion at a comfortable volume. There is about a 15 second time spanon its way down, that the quality of the distortion is truly remarkable. When it's fine, it's perfect..not a trace of distortion.It doesn't produce any bad noises like clicks,pops, or hissing to lead you to suspect any particular part. Tim</P>


[/quote]</P>


Tim;</P>


http://www.geocities.com/OrganMate/</P>


Cheers</P>


Dave</P>
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[Tim Rinkerman]

Re: Fuzzy Sound



Thanks,Dave...</P>


That's where i got the installation instructions... Tim</P>