DC-5 Volume Swells

[dante]

I don't know what happened to my DC-5b combo, but it started acting strange last week. I was practicing at home at a very low volume when the volume just jumped to a slightly louder level arbitrarily. I attributed it to my having the volume teetering between 'off' and 'too-****-loud'. As any DC-5 owner knows, it's a delicate balance at low volume.

At our gig last weekend, it happened again. First set went just fine, we took a break and came back to the stage, then my amp was really loud. I was able to determine that it was only the clean channel that was being affected, but still had no idea what was going on.

I decided that I'd go ahead and perform the volume mod (snipping the leg of the little resistor) and took the amp out of the chassis only to find that the mod had already been done (doh!), so I put the amp back together.

I also consulted a good friend about the issue I was having and he suggested that the culprit was probably a bad volume pot (either the Gain or the Master) in the channel. So, now that the amp is back together, I need to pull it out again to change the pot (doh!)

After putting the amp back in the chassis, I powered up the amp. It made a strange sound (like a fizz or crackle) and the light went out. The amp will no longer power up at all. I checked the fuse, it has not blown.

What on Earth have I done? Any info would be greatly appreciated

 

[D2dark]

Send it to a pro or mesa directly.

 

[dante]

UPDATE: I did a LOT of reading online to diagnose what could have happened. A couple of things I read suggested a bad phase inverter tube, bad power tube, or a misaligned tube causing the fuse to blow. I didn't think the fuse was blown....but, upon further inspection, it was.

I bought 5 new fuses for $4 a the local auto parts store, put one in the amp and it worked fine for 30 minutes last night. I put the extra fuses in the little footswitch pouch in the back of the amp for future use. In all my years of playing (over 30 now), this is my first blown fuse. I have been told a million times to carry extra fuses and always ignored it....no more.

I am assuming a crooked or loose tube caused the fuse to blow, since it happened just after I put the amp back together. So far so good


I still have yet to solve my volume jumps - but I can systematically replace the pots until I find the culprit

 

[Monsta-Tone]

Keep an eye on your power tubes. I had a 5150 II that had serious volume spikes. A fresh set of power tubes solved the problem.
Your power tubes are also almost always the culprit when it comes to blowing fuses.
This is the 1st thing that comes to mind.


Other possible causes for the volume jump (there are probably more, but it's early here):
Preamp tube, clean channel would be V1 or V4, although it could be any of them.

Dirty Send Jack on the FX Loop. I just had to replace the one in my Maverick. The amp would work fine on the clean channel, but the lead channel would fizz out and lose volume after a few minutes.
A quick check would be to insert a patch cable between the Send and Receive when the volume swells are occurring.

Bad volume or gain pot - These pots are notorious for becoming loose. A simple fix is to squeeze the little tabs (that hold the back of the pot to the front of the pot) back together.

Bad Output Volume pot - I know it's only happening in one channel, but I have still seen this.

 

[dante]

Thank You Sir

I have new power tubes on the way. I just replaced all the preamp tubes recently, so I don't suspect them....yet. Thanks for the troubleshooting tips. I will try the tab squeezing trick - that's awesome. If that doesn't work, I'll start replacing.

When the volume swells are occurring, if I connect the send & receive - then what?

I'm not currently using the FX loop, does that matter?

 

[MJ Slaughter]

When the volume swells are occurring, if I connect the send & receive - then what?

I'm not currently using the FX loop, does that matter?

It seems like it shouldn't matter but it can. If I remember correctly monsta-tone told me that the send jack has a switch so if the fx loop isn't used for an extended period of time corrosion can screw with it. I was experiencing crackling sounds and volume inconsistencies on my DC-3. After cleaning the jack good, contact cleaner and inserting male jack in and out several times, it cleared up and works great. I just acquired a DC-5 head and the first thing I did was clean all pots and jacks.

 

[dante]

Thanks MJ,

(and Monsta) I'll clean out all the jacks & I want to take a good look at all the pots anyway. Sounds like a fun project for the weekend...unless the weather's nice, then the motorcycle beckons

 

[dante]

Okay, I opened up the amp yesterday and crimped the little tabs tighter on all pots I found with tabs. I sprayed D-Oxit into the Send and Receive jacks for the FX loop and inserted a cord 500 times into each one to clean them out. I left a small patch cord in the loop to keep dust from getting inside. I have a couple of Switchcraft jacks on reserve, should they need to be changed.

I played for a couple hours yesterday without any volume swells - let's see how long it lasts (crossing fingers)

MODERATORS: I seem to have covered a couple of topix in this thread. If you feel like splitting the bulk of this into a new "Volume Spike Issues" thread, I totally understand