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Post subject: Speaker magnet interference
Posted: Fri Apr 29, 2016 4:58 am
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Ive got this strange intermittant noise at higher power volumes on my blues deville 212.
Was recently at a good amp tech where the chassis was on the bench.....scoped....ect, and no problem found. It was concluded that a questionable speaker connection was the problem, and repaired.
.
Unfortunately, that helped a lot........but I still hear it on strong higher notes occasionally.
Almost so infrequently that its not a big deal.
The tech confirmed that the hand wired deville chassis was certainly constructed very well with top notch components.
.
I am wondering if one of my power tubes up almost against the texas heat speaker isn't possibly a cause.
A high plate current being affected by the strong magnetic field?
btw.....the amp sounds awesome....and seems louder than my 69 twin reverb with the exception of these occasional scratching noises.
All tubes have been switched out repeatedly with no solution.


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Post subject: Re: Speaker magnet interference
Posted: Fri Apr 29, 2016 9:32 am
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Your problem is probably in the internal switching of the External Speaker jack.
It's a common problem in the Deluxe/DeVille series.
The speaker circuit is routed through the NC contact of the Ext jack and will intermittently drop out the signal at hi power peaks.
Clean the contacts with card stock and solvent between the contacts.


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Post subject: Re: Speaker magnet interference
Posted: Fri Apr 29, 2016 9:37 am
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There is no internal switching.
The chassis was gutted and ptp wired for me at Tube-Tone amps. It was a one off.
I believe the problem is either with a speaker under high clean volume rubbing the coil....or the speaker magnet being too close to the Tung-Sol 7581A power tubes.


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Post subject: Re: Speaker magnet interference
Posted: Fri Apr 29, 2016 9:38 am
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Wait a minute....I must've not read closely.
Maybe it could be the speaker jacks themselves on the chassis.
Thanks Tims Audio.


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Post subject: Re: Speaker magnet interference
Posted: Fri Apr 29, 2016 5:53 pm
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Try the chassis (the amp) outside the cab with speaker extension.

You see/ hear if it is the magnet


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Post subject: Re: Speaker magnet interference
Posted: Mon May 02, 2016 8:56 am
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It's more likely to be vibration from the very close speaker rattling the internal components of the tubes. I'll bet it goes away with an external speaker (a cab sitting under the amp doesn't count).


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Post subject: Re: Speaker magnet interference
Posted: Tue May 03, 2016 6:27 am
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A tube or speaker rattle is a pretty consistent symptom that is generally frequency dependent.
The OP described a highly intermittent dropout that wasn't frequency sensitive.
The switching in the External Speaker jack causes a hi power and highly intermittent dropout. It's a common issue on the HRDX.
You can ckeck for the problem by measuring the resistance across the EXT jack switch.
Do Not move the External jack switch contacts or you'll chase away the symptom.
Insert a piece of cardstock in the INT speaker jack switch as you remove the speaker plug.
With an ohm meter, measure from the green wire on the INT speaker jack to the Green/silver stripe wire on the EXT speaker jack.
A good jack switch will measure less than .5 ohms. A reading over that indicates a potential problem.


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