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Post subject: Fender Deville 2x12 intermittent crackle/distortion
Posted: Tue Nov 15, 2011 7:42 am
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I have a 2x12 Deville that I've owned since new. It is an older US made version, purchased probably around 2000 or so. I've recently re-tubed it (preamp and power tubes) and I have done the Fromel mods to it. (See here: http://fromelelectronics.com/modificati ... od-DeVille)

Prior to the re-tube and mods, the amp had the periodic issue I've seen described elsewhere which was an intermittent sort of crackle/distortion when certain low noted were played. While this issue has gotten a bit better (due mainly, I believe, to the mod to the tone controls that allows greater control over the amount of bass produced by the amp), the issue still exists. Other than that it sounds fine.

Now, between the new tubes and the Fromel mods I figured the issue should have been solved. The Fromel mods replace all of the electrolytic caps in the amp, several resistors (plate resistors and the two dreaded power resistors), input jacks, etc.

So, my question now is this: what are the chances that one or both of my speakers may be on their way out? What is the easiest way to tell? Since they still function OK except for certain notes, I wasn't sure that measurements would be helpful.

Any advice would be appreciated.

Thanks,
Joe


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Tue Nov 15, 2011 8:16 am
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Try another set of known, good speakers through the AUX/EXTERNAL speaker output (if the amp had one). Disconnect the onboard speakers.

Also may want to check all the solder points in the amp. Almost sounds like a cold solder point(s).


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Wed Nov 16, 2011 11:19 pm
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I had the same exact amp with a very similar issue if not the exact issue.. After many upgrades to the board and a ton of other boring details I found it was a simple fix.. I opened the back. Keeping in mind of the high voltage capacitors.. The back end cover of the amp has aluminum tape.. Which is used to block interference. I ensured that all wires were secured below the chassis and not touching the aluminum tape. Also I replaced the aluminum tape with new stuff from Home Depot and cutting it so that it does NOT touch the chassis. This solved my issue as the tape was causing interferiance by rubbing on the wires that run in an through the backside of the amp.


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Thu Nov 17, 2011 10:14 am
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Hi joeriz,

Great suggestions so far. I doubt if your speakers are the issue. I would first make sure that the bias is set properly, it was likely cold from the factory and could be even worse with the new tubes. If bias is good, then I think that you might be correct and that maybe what you are/were hearing is too much bass/mids, evident when playing certain low notes/chords when trying to play clean. Does it sound as if the tubes are on the verge of breakup when playing clean, especially when you dig in on the low notes? This can be even more evident when using hum-bucker pups. With the new tone stack caps, you may be able to lower the bass and/or mid pots to dial out that sound. With the treble knob at 6, try lowering the bass and mid pot to 1 and see if that sound is gone, then raise them until you start to hear it again. You might find a setting with very low mids and a bit more bass beneficial, or the bass very low with higher mids. You can't get huge bass with the open back combo anyway. Just another guess to consider. :idea:

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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Fri Nov 18, 2011 5:26 am
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Thanks for the suggestions thus far. I will have some time this weekend to mess around with it and see if I can trace the cause of the sound.

After doing the mods I described above I did re-bias the amp hotter than it came stock. I have it set to 70mA right now which seemed to be a happy medium between the stock 'cold' value and cooking the tubes. I have also messed around quite a bit with the modified tone controls - typically keeping the bass at 0 - to no avail.

I will report back after I tinker with it some more.

Thanks,
Joe


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Fri Nov 18, 2011 9:59 am
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70 mA at the test point is still cold for this amp, that's less than 50% idle (if your Plate volts are about 485). 70 mA at the test point is Cathode current for both tubes. Divide by two, then subtract grid currents (5 mA), and you have 30 mA of Plate current for one tube. Multiply that by the Plate volts and you have around 14.5 watts of idle dissipation (.030 x 485 = 14.5).

So really, 75 mA at the test point would be a minimum setting for a 30 watt tube in this amp, at just over 50% idle (15.5 watts). Around 95 mA at the test point would be a maximum setting at about 70% (21 watts).

Having the amp biased too cold (as here) can cause more distortion than when biased a little hotter. :idea:

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Fri Nov 18, 2011 2:11 pm
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+1 Shimmilou
But ONLY ONE test point for both tube is a problem if tubes are old , they could be unmatched and one could have a bias too hot.

Imo the problem of joeriz is probably a bias or/and tube defective and also could be some solder or connexion in high voltage


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Post subject: Re: Fender Deville 2x12 intermittent crackle/distortion
Posted: Sun Nov 20, 2011 2:39 pm
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Just wanted to post an update...

First, I did increase the output tube bias to 80mA. That did not eliminate the intermittent crackle - I didn't really think it would - but wanted to try it out anyway. It didn't seem to make any real difference in the sound of the amp.

After much poking around looking for a bad solder joint inside the amp, I traced the problem to the ribbon cable on one of the preamp tubes. I re-soldered all of the solder joints for the ribbon cable (actually did this for all of the ribbon cables for good measure) and all appears to be well now.

Thanks again for the suggestions.

Joe


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