Wow, preamp tubes would basically make my master volume half powered? Interesting. I will have a look when I get home. Thanks guys!
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Mesa Boogie Walkabout Mega-thread Part 10
- Thread starter Chef
- Start date
Takes more master volume level to output a weaker signal coming from the preamp. If find you have all 12AX7's in both positions in each of your amps, try switching the tubes between the two amps and try it out. Not every 12AX7 is equal either.
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Thanks again. Seems most logical. Will let you guys know what it is. I did find the following in a another walkabout thread.
Amplification factor
12AX7 100%
5751 70%
12AT7 60%
12AY7 45%
12AV7 41%
12AU7 19%
Going to grab it from rehearsal space on my way home tomorrow and check.
Amplification factor
12AX7 100%
5751 70%
12AT7 60%
12AY7 45%
12AV7 41%
12AU7 19%
Going to grab it from rehearsal space on my way home tomorrow and check.
I used to have two Walkabouts that looked identical and had serial numbers within 100 of each other, but one had Mesa Russian 12ax7s and one had Mesa Chinese 12ax7s and the two sounded and acted WAY different. I could switch the tubes between the amps and the characteristics followed the tubes. One amp seemed much gainier and got much louder at 12o'clock as a result, so I would guess that is indeed your issue! Both tubes will affect this by the way. I've had good luck with JJ 12ax7s in mine after needing to replace a malfunctioning tube and the Gain/output level seems very much on par with the tubes it replaced (the higher gain tubes I mentioned before). Mesa may well have used JJs back then (they do now), so they could be the same tubes.
EdwardofHuncote
I Still Dream of Jeannie
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Need some help fellas...
Had an outside gig this afternoon. Ran at a little higher volume than usual... input gain at noon, master volume at about 10:00. I had the lows and mids pushed a couple db, the highs and standard 60 hz rolled off a touch...
Noticed for the first time one of my Scout cabs is making an annoying distortion/buzzing sound. It seems very focused around the upper-left of the cab, (at the tweeter?) and is most noticeable on the mid and upper mid frequencies, *especially* the open G. It's hardly noticeable in the lower register, even at low B, or in the extreme bright end of the eq spectrum. And for whatever reason, it seems more obvious when running both Scout cabs together.
Likely culprit(s)?
Trouble-shooting options?
As always, Thanks!
Had an outside gig this afternoon. Ran at a little higher volume than usual... input gain at noon, master volume at about 10:00. I had the lows and mids pushed a couple db, the highs and standard 60 hz rolled off a touch...
Noticed for the first time one of my Scout cabs is making an annoying distortion/buzzing sound. It seems very focused around the upper-left of the cab, (at the tweeter?) and is most noticeable on the mid and upper mid frequencies, *especially* the open G. It's hardly noticeable in the lower register, even at low B, or in the extreme bright end of the eq spectrum. And for whatever reason, it seems more obvious when running both Scout cabs together.
Likely culprit(s)?
Trouble-shooting options?
As always, Thanks!
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Is it in the combo cab? I had a connection in the built-in speaker cable of mine get a bit loose at one point that I had to reconnect inside the 1/4 fitting. It would cause intermittent noises with vibration that were most audible through the tweeter.
Also might want to try swapping out different preamp tubes- I've had a couple tubes go bad in my Walkabout and cause noises.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
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Thanks sunbeast. 
Yes, the WA is currently docked in a Scout combo cab (8ohm) with another combo cab in tandem.(also 8ohm) I checked pretty thoroughly for loose connections, but the noise is constant rather than sporadic, and very concentrated in frequency around that open G note. I swear it sounds like a blown speaker, just not the big one.
It could be a preamp tube breakup thing... it's definitely a distortion sound sorta' like grossly overdriving the input. I've got some time to mess with it today... I have three Scout 12's another Scout 15, and two different Walkabout heads so hopefully I can eliminate step-by-step.
Yes, the WA is currently docked in a Scout combo cab (8ohm) with another combo cab in tandem.(also 8ohm) I checked pretty thoroughly for loose connections, but the noise is constant rather than sporadic, and very concentrated in frequency around that open G note. I swear it sounds like a blown speaker, just not the big one.
It could be a preamp tube breakup thing... it's definitely a distortion sound sorta' like grossly overdriving the input. I've got some time to mess with it today... I have three Scout 12's another Scout 15, and two different Walkabout heads so hopefully I can eliminate step-by-step.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,649
- 2
- 16,417
- Disclosures
- I privately own and operate a local musical instument repair shop.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,649
- 2
- 16,417
- Disclosures
- I privately own and operate a local musical instument repair shop.
I've had the 12" driver out before but never the tweet, never even looked up at it... is it as simple as unplugging?
EdwardofHuncote
I Still Dream of Jeannie
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Okay... after some testing, using a very similar, yet alternate Walkabout head, three different basses, (2 actives and a passive) different cables and connectors, and several combinations of Scout cabs, here is a (possibly wrong) conclusion.
To start with, it's a funny coincidence that my solution may be found in responses to honkimon's preamp tube issue on this same thread page. I think sunbeast is right regarding the preamp tubes, here's why:
The sound I'm hearing is definitely a fuzzy distortion from the input side. It's present even at lower volumes in every Scout cab I have, though in varying degrees, but especially in the Scout 12 that the Walkabout is currently docked in. *This cab has a newer 12" PH (8ohm) driver installed.
When I connect this same cab, or any of the other Scout cabs to an alternate Walkabout head the fuzzy distortion sound is completely gone.
To summarize - it's as if "clean" input gain isn't possible with the offending unit even when set below 12:00. If I set the input gain at anything past 1:00, (which I never do in the normal course of playing) the mids and highs start breaking up. At 2:00 it sounds really unhappy. Low frequency response however, seems mostly unaffected.
So... given those conditions, should I go shopping for some new 12AX7's? Are there other potential angles I should be looking at?
As before, many thanks!
To start with, it's a funny coincidence that my solution may be found in responses to honkimon's preamp tube issue on this same thread page. I think sunbeast is right regarding the preamp tubes, here's why:
The sound I'm hearing is definitely a fuzzy distortion from the input side. It's present even at lower volumes in every Scout cab I have, though in varying degrees, but especially in the Scout 12 that the Walkabout is currently docked in. *This cab has a newer 12" PH (8ohm) driver installed.
When I connect this same cab, or any of the other Scout cabs to an alternate Walkabout head the fuzzy distortion sound is completely gone.
To summarize - it's as if "clean" input gain isn't possible with the offending unit even when set below 12:00. If I set the input gain at anything past 1:00, (which I never do in the normal course of playing) the mids and highs start breaking up. At 2:00 it sounds really unhappy. Low frequency response however, seems mostly unaffected.
So... given those conditions, should I go shopping for some new 12AX7's? Are there other potential angles I should be looking at?
As before, many thanks!
You say it just started happening? I wonder if it might be the Driver tube- I'm not sure what would happen audibly if that one started having noise issues... I tend to play with some overdrive all the time, and have always hated the way the tweeter works with it in my Scout cab (and probably most tweeters, but in a single woofer cab the harshness of the tweeter can be very noticeable).
Just to verify its a tube, you should try switching out a tube that you KNOW is fine (ie V1 from your other Walkabout) into each position of the offending amp one position at a time to see if it clears up.
Just to verify its a tube, you should try switching out a tube that you KNOW is fine (ie V1 from your other Walkabout) into each position of the offending amp one position at a time to see if it clears up.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,649
- 2
- 16,417
- Disclosures
- I privately own and operate a local musical instument repair shop.
Just noticed it Friday... may have been going for a while, but Friday was a pretty loud outside show.
Plus I hadn't used the 2x Scout rig lately... been using a different Walkabout head in a Scout 15.
Good plan switching out tubes with a known; I'll do that tonight/tomorrow.
Thanks 'beast!
Turning tweeter off is just turning the tweeter volume all the way down.
But. .. Yes, sounds like it could be a tube. As SB said, swap with a known good one. 12AX7s are pretty cheap so it's always a good idea to havea couple of good ones spare.
Search this thread (or maybe an earlier 'part' of it and you'll find a fair bit of info re tube swapping in Walkabouts.
But. .. Yes, sounds like it could be a tube. As SB said, swap with a known good one. 12AX7s are pretty cheap so it's always a good idea to havea couple of good ones spare.
Search this thread (or maybe an earlier 'part' of it and you'll find a fair bit of info re tube swapping in Walkabouts.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,649
- 2
- 16,417
- Disclosures
- I privately own and operate a local musical instument repair shop.
Wow. Without spending two weeks reading the vacuum tube chronicles, I'm assuming just ordering a stock set from MesaBoogie would cover me...? My needs are pretty simple - I just want to get my clean gain back and simultaneously get rid of this fuzzy noise that's corruptin' my groove.
Reluctantly, (because I hate screwing with something that works) I'm going to swap the tubes from my two Walkabouts this evening. If that cures the ill, then I'll go on and order a set. As rodl2005 said a few posts back, wouldn't hurt to have a couple new ones in the gigbag anyway.
Update to follow. Thanks to all the Walkabout Megathread regulars - you guys are awesome!
Wow. Without spending two weeks reading the vacuum tube chronicles, I'm assuming just ordering a stock set from MesaBoogie would cover me...? My needs are pretty simple - I just want to get my clean gain back and simultaneously get rid of this fuzzy noise that's corruptin' my groove.
Reluctantly, (because I hate screwing with something that works) I'm going to swap the tubes from my two Walkabouts this evening. If that cures the ill, then I'll go on and order a set. As rodl2005 said a few posts back, wouldn't hurt to have a couple new ones in the gigbag anyway.
Update to follow. Thanks to all the Walkabout Megathread regulars - you guys are awesome!
I recently replaced the stock Mesa tubes in my WA with ECC83 tubes from JJ. They're 12AX7s, and they sound great! Plus, they were cheaper than the Mesas.
EdwardofHuncote
I Still Dream of Jeannie
- Aug 21, 2013
- 6,649
- 2
- 16,417
- Disclosures
- I privately own and operate a local musical instument repair shop.
This ^ is what was in the WA head I thought might be at fault... both v1 & v2.
The other head had stock Mesa Russians, also in both positions.
Unfortunately, exchanging the tubes from head to head made no difference... I've still got a wicked midrange-y distortion in one of the 8ohm Scout cabs. I swear it's coming from the tweeter... pulled the grill off just to get closer. If the input gain is intentionally overdriven, it becomes very obvious.
Gotta quit for tonight... guess tomorrow I'll get into the cab/speaker.
Attachments
Bummer! I've been fortunate that all my WA-related issues have been fixable with a new pre tube in V1. I've been meaning to physically disconnect the tweeter/crossover in my Scout cab for awhile though!
