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PostPosted: Mon Jun 11, 2018 9:48 pm 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
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Is it normal for the different modes in channel 1 to have radically-different volume levels? "Clean" is down about 5 dB from "Fat," which in turn is down another 5 dB from "Tweed."

If this is abnormal, what is a likely cause? Preamp tube? If so, which one? Maybe V3, since neither channels 2 nor 3 seem to be affected?

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PostPosted: Tue Jun 12, 2018 2:30 am 
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Mark III

Joined: Sun Sep 27, 2015 2:50 pm
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It's normal, well, that's the way it is on my Mark V too. I don't notice it so much between clean and fat modes but tweed is definitely louder. Pretty sure this is mentioned in the manual. It's to do with the changes the different modes make to that section of the preamp.

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PostPosted: Tue Jun 12, 2018 3:03 pm 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
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Good to know. I have enough other problems with this amplifier (a late 2016 90-w combo that's never been on the road and that I've only been using on a daily basis since about last August): weird crackling noises, sudden volume losses, massive breakup, the momentary power losses as described by others here: http://forum.grailtone.com/viewtopic.php?f=33&t=74584.

I guess my first step will be replace all the power tubes, a pair at a time, and then go through the individual preamp tubes and possibly the rectifier tube which apparently is implicated in the power-off problem (although I use the first two channels in 90-w mode which should be using the silicon rectifier, and it's mostly those two channels I run into problems with).

I know the Mk V is a very complex amp, but it's kind of disappointing to be having these sorts of weird, intermittent, hard-to-troubleshoot problems. But then days will go by when the amp is fine, and then it sounds absolutely gorgeous. So I suppose it's worth it.

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PostPosted: Wed Jun 13, 2018 12:49 am 
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Mark III
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Joined: Wed Apr 02, 2014 1:55 am
Posts: 311
Location: California
The differences in modes are normal. And I wish that all the clean modes were at the same output level as the tweed. But it's not that big of a deal especially at gig level cause the output gets opened up a bit. I keep my channel mode volume levels low and open up the output for gigs. I find better tone with channel mode volume levels low. So at a gig if the clean seems too low in volume, open up the output and turn down the volumes on channel 2 & 3 to balance your mix. Trying to turn up the clean usually jacks up the clean tone clearity.

As for your other issues I would change all the tubes. Get yourself a baseline of all new tubes. Tubes wear but they do actually last quite a long time. When buying an amp used I would establish a baseline. This will also probably correct your problem. Then test the tubes you remove, dump the bad ones and keep the others as spares in a pinch.

I have been collecting tubes for years. I also have a tube tester. I'll purchase a complete set every now and then. Do a complete change every few years just to freshen things up. It is always amazing how different the amp sounds with a fresh set. Tubes wear slowly and your ear doesn't hear it. Gigs not included I play about 6 hours a week at times 8 or 10 hours in a day if I'm writing/recording or rehearsing for a gig. I have a dedicated music room so I get to play a little louder than most people get to practice at so there is wear.

Changing tubes is not a bad thing. Installing a complete set always gives me a bit more confidence in my equipment knowing I'm maintaining the tools of the trade. It's no different than changing strings, cleaning the fretboard, or wiping the tequila off the pickguard. It's just not required as often.

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PostPosted: Wed Jun 13, 2018 11:32 am 
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Mark I

Joined: Sun Aug 21, 2016 10:00 pm
Posts: 33
Putting new tubes in an amp is like putting new strings on a guitar !!!!
When I buy used gear a setup and cleaning is always done ASAP
Just saying

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PostPosted: Wed Jun 13, 2018 11:41 am 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
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Yes, that's my plan. I've already got a pair of power tubes, but I'm going to buy another pair. Replace each pair separately, just to see if the inner two resolve the problem; if not then might as well replace the outer pair as well.

If the problem persists, then it's the rectifier tube's turn. If that still doesn't resolve the various issues, then it's the long, slow grind of replacing preamp tubes. So far it seems that the issues affect at least ch 1 and 2 (3 is harder to tell because I don't typically use ch 3 for long periods of time and these are intermittent problems at best), which leads me to believe the problem child is either V1 or V3, or possibly V7 (since V4 and 5 are only used by ch 3 they're probably not the problem, right?).

What makes this a grind is that since these are largely intermittent problems, I will have to wait two solid weeks at least between preamp tube swaps, unless I can reproduce the problems more often than that. Could take all summer.

Fortunately the amp still has three and a half more years of warranty coverage (I'm the original owner). Also, if it needs to go back to Mesa/Boogie, that's about an hour's drive from here so I don't have to ship it.

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PostPosted: Wed Jun 13, 2018 1:00 pm 
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Mark III

Joined: Sun Sep 27, 2015 2:50 pm
Posts: 285
Location: Good ole England
You could try pull the rectifier tube out as if its faulty it will pull the voltage down even when its not active in your setup. Obviously dont use 10w or tube rectification in 45w mode for this test. It will at least rule it out if the problem persists or could save you some cash if it cures the problem by saving the need to pay out for anything other than a new rectifier tube.

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PostPosted: Wed Jun 13, 2018 1:07 pm 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
Posts: 10
Sounds like a good plan. I tend to run all three channels in 90-watt mode (as I understand it, the tube rectifier is actually in parallel with the silicon rectifier even when using the silicon one, but the amp will run in 90w mode with the tube rectifier removed). Maybe that's a project for this week. It would have to run for at least a week or two in this configuration to be sure (unless the problem persists with the tube removed). I assume it's safe to run the amp for extended periods of time without the tube installed, so long as you're always using 90w mode or the silicon rectifier in 45w mode?

My big fear, of course, is that there are either multiple bad tubes, or that the problem is not tube-related at all. But this sounds like a good first step, given the amp has suffered from volume losses/momentary shutdowns in addition to various other issues.

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PostPosted: Wed Jun 13, 2018 3:13 pm 
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Mark I

Joined: Fri May 06, 2016 10:25 am
Posts: 49
I would say the volume difference in different modes of ch 1 is normal. The reason is that, as each mode adds more gain, the signal starts to clip slightly but is still actually getting noticeably louder. The reason you don't notice it in ch 2 or 3 is because the signal is well into the clipping realm and more gain doesn’t really make the signal much louder but just adds more distortion and compression.

Just think about the volume knob on the guitar. In high gain modes, the volume knob doesn’t do much until you get down to half or lower but in a clean sound the volume change is much more noticeable.

I also have a JVM and ch1 has green orange and red modes, each with increasing gain and the exact same thing happens.

It is just the nature of a clean signal.


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PostPosted: Wed Jun 13, 2018 3:17 pm 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
Posts: 10
Makes sense. Channel 1 is the least compressed of the three channels, so increasing gain will increase volume more than it will in channels where even the lowest gain setting still has a large amount of gain. Just as turning up the input volume on a channel strip with a lot of compression will have less effect than on a channel strip with no compression.

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PostPosted: Wed Jun 13, 2018 3:20 pm 
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Mark I

Joined: Fri May 06, 2016 10:25 am
Posts: 49
emurphy94108 wrote:
Just as turning up the input volume on a channel strip with a lot of compression will have less effect than on a channel strip with no compression.

Excellent way of describing it. Wish I had thought of it that way. 8)


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PostPosted: Fri Jun 15, 2018 2:48 pm 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
Posts: 10
Playing last night, I noted, after about fifteen minutes, massive breakup, volume loss, distortion, etc., in channels 1 and 2 along with a momentary power-loss to the whole amp (not long enough to reset the channel back to 1, but enough to dim the LEDs on the amp and the footswitch). As far as I could tell, channel 3 was unaffected.

Looking at the tube chart in the manual, it looks like V3 is the only tube that is exclusively used by channels 1 and 2 but not by channel 3 (on the other hand, what tube is responsible for channel 3's fifth gain stage? It has six stages, but it seems like no tube does stage five). So I'm going to start there. I'm also going to replace the rectifier tube since it seems that has a reputation for being implicated in sudden momentary power losses to the whole amp.

If that doesn't resolve the issue, I'm going to replace all four power tubes, and if I'm still in the weeds, I guess it will come down to slowly swapping out each preamp tube until I isolate the bad one. Assuming it's even a bad tube! If I can't otherwise resolve the issue, Petaluma is only about an hour away by car.

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Boogie Mk V-90w combo
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PRS CE24
American Standard Telecaster
Standard Stratocaster
Carvin Icon bass
American Elite Jazz Bass V


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PostPosted: Fri Jun 15, 2018 4:24 pm 
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Mark III

Joined: Sun Sep 27, 2015 2:50 pm
Posts: 285
Location: Good ole England
emurphy94108 wrote:
Playing last night, I noted, after about fifteen minutes, massive breakup, volume loss, distortion, etc., in channels 1 and 2 along with a momentary power-loss to the whole amp (not long enough to reset the channel back to 1, but enough to dim the LEDs on the amp and the footswitch). As far as I could tell, channel 3 was unaffected.

Looking at the tube chart in the manual, it looks like V3 is the only tube that is exclusively used by channels 1 and 2 but not by channel 3 (on the other hand, what tube is responsible for channel 3's fifth gain stage? It has six stages, but it seems like no tube does stage five). So I'm going to start there. I'm also going to replace the rectifier tube since it seems that has a reputation for being implicated in sudden momentary power losses to the whole amp.

If that doesn't resolve the issue, I'm going to replace all four power tubes, and if I'm still in the weeds, I guess it will come down to slowly swapping out each preamp tube until I isolate the bad one. Assuming it's even a bad tube! If I can't otherwise resolve the issue, Petaluma is only about an hour away by car.


If i recall correctly V3 is Ch3 stage five. Just a miss-print in the manual. Gonna be a trial and error process for you i think. Keep us posted.

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Her highness the Veenus
(Mark V/V4 & V7 12AT7 Combo)

2 x 12 Vertical Cab
GSP-1101

Gibson LP Studio with alnico ii pro
Schecter C1-XXX with emg 81/85 18v
Jackson Dinky XL with Duncan designed???
Sigma DNC-1STE


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PostPosted: Wed Jun 20, 2018 10:05 am 
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Mark III
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Joined: Wed Feb 27, 2013 12:45 pm
Posts: 330
Location: Southwest Michigan
I bought my V used. The first thing I did was replace all the tubes since the seller told me the tubes were original from 2009. I would also recommend using a can of DeOxit on the tube sockets. Mine had to be thoroughly cleaned with tiny bottle brushes. Fortunately, DeOxit makes a kit for that as well. It's a PITA, but definitely worth it.

I got my kit from Amazon:
https://www.amazon.com/Hosa-SKGXMDBULK- ... deoxit+kit

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PostPosted: Wed Jun 20, 2018 10:33 am 
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Bottle Rocket

Joined: Mon Jun 11, 2018 9:35 pm
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That kit looks worth having, given the sheer number of valves in this thing. I bought my Mk V new in late 2016, and for the first eight months or so rarely used it (I live in a small studio apartment in downtown San Francisco, and if I told you my rent it would turn your hair white). But since about August of last year I've been using it for an hour to an hour and a half a day, mostly practicing Bach 2-part Inventions (so far no complaints from the neighbors).

Given the material, I'm not indulging in huge amounts of gain, and with the effects loop active I can keep the volume under control using the master output control. I have, however, developed a recent affection for the "Crunch" mode in channel 2, which gives me a nice warm round tone which works surprisingly well for material written three hundred years ago.

In any case, as noted above, the issues I've been having with this amplifier are ludicrously intermittent. Since I've now accumulated a full compliment of replacement valves (the more I write "tubes" the more I dislike the term, since it's not really all that descriptive)—four 6L6s, two 12AX7s, and a 5U4GB, the amp has performed flawlessly, even though I haven't replaced a single valve yet. Maybe just the threat of replacing them has done the trick.

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Standard Stratocaster
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