channel volume fluctuating- master pot going?

[fdesalvo]

Like the title says, my channel volume is fluctuating at low volumes. A tap on the chassis will often bring it back up, but it will still act up.

Since both channels are exhibiting this behavior, should I assume that it's the overal master volume potentiometer? It doesn't seem like it would too hard to swap out...

 

[redmax61]

I've actually had output tubes cause that. Try turning the volume up to about stage levels and smack the amp on top. If it emits a "ping", it's your output tubes.

 

[Boogiebabies]

What kind of Mesa is it?

 

[fdesalvo]

Its a DC-10 head. I've observed the o/p tubes when this behavior occurs and there is no visual indication of anything awry-no flashing lights or fireworks!

Also, none of the tubes are making any mechanical noise and I haven't had this occur at stage volume!

 

[fdesalvo]

Well, I swapped the powertubes to no avail Looks like I'll be calling tech support on tuesday...

 

[jukesgtr]

This is my response to another post today, check the pots in yr amp to eliminate them as a possible cause for your problem.
----------------------
I went and got new tubes for my Peavey C30 because I thought one of the power tubes was bad....changed all tubes and the trouble was still there. Notices the bad/rattling sound (on certain notes played on lower register that REALLY sounded as a tube problem) came from a one scratchy pot in the amp, vibrating i.e. contact/no-contact when playing!! Sprayed all pots with contact cleaner that solved the problem.

PS: I still needed spare tubes for the amp so these new JJs will not be wasted!

 

[jukesgtr]

You said @ low volume level so the amp does not vibrate that much, the pots probably are not then the cause....but on the other hand I was not playing that loud....clean the master pot with contact spray anyway before trying replacing it...

 

[fdesalvo]

Thanks for the responses, but I was mistaken; I noticed this occurring at high volumes tonight

 

[jukesgtr]

Still buddy, try first to clean the pots with contact spray, it is a cheap way to eliminate simple problems some techs charge a lot for.

How old is your Boogie and where it has been? High humidity may cause rust and bad contacts even in pretty new amps. Pots and input/output connectors (i.e. anything with a mechanical contact!) are the first places to look at after the tubes I guess?? Spray the tube sockets with that contact cleaner too. You can get it at Radio Shack for example.

 

[fdesalvo]

Thanks for the tips, man. Haha, I can build a **** amp from scratch, but never had to troubleshoot the blasted things.

 

[fdesalvo]

Update:

I used contact cleaner in all volume pots and it didn't make any difference. On top of that, it's left some residue in the pots. Oh, well.

I also put a spare SPAX7 right next to V1 in the V2 slot just for craps and giggles. It's lowered the noise floor significantly and I don't notice a reduction in the gain department! I can't wait to the amp once it's sorted out.

So, when Mesa opens up after the holidays, I'll order 3 volume potentiometers so I can rule them out.

The caps look straight forward and are holding a charge just fine. There are no obvious physical deformations or leaking fluids... I really don't want to have to send this **** thing to Boogie.

 

[screengrid]

Hi, unfortunately I have no schematic of the DC 10. But my experience with my MK IV is, that all the less strange effects / problems which occured over already 15 years now, were tube problems. Also such effects like volume jumps ( Mostly bad power tubes )
Ok, if not already done, I would recommend you to substitute also testing wise every preamp tube, one after the other with a as new/good known tube.
Try to provoke the failure after each changing step and keep patience.
Sometimes it lasts a while, until the failure reproducible occurs.

If that doesn't help and no other simple failures like bad jack connections, pot's etc. are the reason, the amp should be taken to a good amp tech or better to Mesa Boogie.

Good luck

 

[redmax61]

Actually Frank, I'm a "twidget" (that's the short name for an Electronics Tech) for the US Navy. It sounds to me like your troubleshooting skills are just fine!

 

[Howitzer]

Hey, when I bought my Recto- I had the same problem, it ended up being either the Capacitor or the transformer- I cant remember which.

It would fluctuate randomly, and when i would crank it, it would sometimes lose all its volume. It actually happened at a show once, very embarrasing. Mine would also respond to physical abuse - So, Call mesa (if you havent already).

Alternatively it could just be a loose solder.

-Matt

 

[fdesalvo]

Thanks for all of your attention, guys!

Actually Frank, I'm a "twidget" (that's the short name for an Electronics Tech) for the US Navy. It sounds to me like your troubleshooting skills are just fine!

red, haha, my cousin is a radar tech in the Navy and they just moved him to Diego Garcia! Man, you military guys rock and we appreciate everything you've done and continue to do for us.

 

[redmax61]

red, haha, my cousin is a radar tech in the Navy and they just moved him to Diego Garcia! Man, you military guys rock and we appreciate everything you've done and continue to do for us.

Thank you.

Actually, my job is relatively simple at the moment. I just finished a tour aboard a Carrier (the USS Ronald Reagan) and transferred to a desk job on the beach. All I do now is assist in making sure that the 1's and 0's flow in the right direction so that the bad guy goes "BOOM!" when the little red button gets pushed.

 

[fdesalvo]

OK, I was just looking at the tube layout of the DC-10 and I may have to reconsider the preamp tubes now. The only tubes which effect both channels are v1 and v6, so I will try to swap these out this evening. You know, this problem only occurred after I swapped in a fresh set of tubes from Boogie.

Actually, my job is relatively simple at the moment. I just finished a tour aboard a Carrier (the USS Ronald Reagan) and transferred to a desk job on the beach. All I do now is assist in making sure that the 1's and 0's flow in the right direction so that the bad guy goes "BOOM!" when the little red button gets pushed.

Dude, before my cousin left for DG, his ship escorted the Reagan around central america, I believe. This was when he was stationed in MS, though.

 

[redmax61]

I was on the SA transit. We went through the Straits of Magellan. That was a really amazing ride! I have pics of me standing on the flight deck in my fowl weather gear in the middle of June. It was freezing out, but the view was so spectacular I couldn't go below decks!

 

[fdesalvo]

The culprit was either v1 or v6- I swapped them both and the volume swelling is gone. I must've gotten a few bad tubes from mesa.

Edit:

AHHHHHHHHH! It's at it again! And the noise on the lead channel is driving me apeshit! :x

 

[fdesalvo]

Alrighty, I pulled the chassis and sat it on top of the 1960a and went to town. I pulled v2, 3, & 4. I replaced them with some older mesa tubes and the noise is completely gone now and she's whisper quiet at stage volume.

Apparently, I got a few bad tubes from Mesa. Case closed.