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Post subject: custom vibrolux issue
Posted: Sat Jan 04, 2014 4:15 pm
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[url][/url] so I just got a used custom vibrolux from a friend of mine its not working quite right but I got it for a steal. The problem it's having is it's getting really distorted and flabby around 2-3 on the volume. My first assumption was the tubes I inspected all of the tubes and all of the pre amp tubes are glowing fine and look to be in good condition. The power tubes looked rather old so I swapped them out with a new set of 6 rated gts but the problem remains. There is also a loud rattle but I assume just a loose screw.

Maybe a bias issue?
Any help would be appreciated

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Post subject: Re: custom vibrolux issue
Posted: Sat Jan 04, 2014 8:22 pm
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stratgeek, Welcome to the Forum! :D

Try a known good 12AX7 in V1 and V2 input socket positions and see if that helps. If this doesn't help, you could have a couple or more cheesy main filter caps under the doghouse. May want to take a look. You need to pull the chassis out of the cab, discharge the main caps (power cord unplugged), remove the sheet metal lid over the main caps --- to inspect.

For poor bass & transient response, it's usually the first two caps off the rectifier that are the main problem (C31 & C32 in your amp). These are the caps that directly feed B+ and the output tubes. Though, I always replace all caps, if poor filtering and power reserve is the issue.

http://www.webphix.com/schematic%20heav ... manual.pdf


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 3:30 am
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Bias ? No

Try some new 12XX7 tubes as BMW write , replace the Phase Inverter tube , 12AT7 (?) close to the 6L6.
Tube glowing do not mean they are good

Same trouble on old vintage amps I replace all bypass caps ( 25 mfd electrolytic ) and check all resistors value on Phase Inverter circuit and replace wrong one.



But Custom Vibrolux amp is a" new" amp , must not need new caps . Is it a printed circuit board ?
If yes , check solder on printed circuit on power supply , Output tubes'sockets


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 6:35 am
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It could be several things, this just happened on my Super-sonic 22 with the stock JJ 6V6s, I put in a pair of new power tubes (and re-biased, which is neccesary with new tubes on this amp), and all returned to normal.

Always try the power tubes first. They're normally the first tubes to go, not the preamp tubes.


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 9:04 am
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Ruger,

OP stated: " The power tubes looked rather old so I swapped them out with a new set of 6 rated gts but the problem remains. "

So, I'd try new 12AX7's before trying another set of output tubes. No?


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 11:39 am
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So I replaced v1 with a 12ay7 and turned the bass to "2" that seemed to help. The amp does still get flabby when volume or bass are turned up. Is this just weak stock speakers?

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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 11:54 am
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Don't think it's the speakers. Sounds like a bad coupling cap or bypass cap in the gain stage. Is this flabby bass in both channels? If so, maybe try another 12AX7 in the phase inverter (V6) position.

Good luck! Tell us how it worked.


http://www.webphix.com/schematic%20heav ... manual.pdf


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 12:20 pm
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BMW2002Ti wrote:
Don't think it's the speakers.




+1


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 12:21 pm
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BMW2002Ti wrote:
Ruger,

OP stated: " The power tubes looked rather old so I swapped them out with a new set of 6 rated gts but the problem remains. "

So, I'd try new 12AX7's before trying another set of output tubes. No?


I don't disagree, however I have had NEW power tubes die very prematurely... I just got a Super-sonic 22, and one of the stock Groove Tubes (JJ) died within a week!!! My point is, in all my years playing tube amps, the tubes are usually the culprit, and more often the power tubes than the preamp tubes. So I always start with new (or known good) power tubes.


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 12:30 pm
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Ruger, you had new JJ 6V6S go bad in a week? These are prolly one of the toughest 6V6 type tubes made today. What is the idle bias dissipation you are using with that amp?


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 12:54 pm
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BMW2002Ti wrote:
Ruger, you had new JJ 6V6S go bad in a week? These are prolly one of the toughest 6V6 type tubes made today. What is the idle bias dissipation you are using with that amp?


IDK.... I didn't even check the bias, I was still in the "plugging it in and just playing it" stage. I have since put another pair of known-good JJs in, and set the bias @23, but I didn't check the plate voltage or anything, need to do that.

Maybe coincidentally?..... I was only able to get the tubes to within 4ma of each other... not sure how close they are supposed to be? When I set bias at 23 that was the high tube... the other one was at 19.


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 12:58 pm
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ruger9 wrote:


I don't disagree, however I have had NEW power tubes die very prematurely... I just got a Super-sonic 22, and one of the stock Groove Tubes (JJ) died within a week!!!

Wrong bias

My point is, in all my years playing tube amps, the tubes are usually the culprit, and more often the power tubes than the preamp tubes. So I always start with new (or known good) power tubes.

I fix amps since long time and more than half of the time it is not a tube

But it is a good habit to start with new tube and easy for anybody


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 1:03 pm
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ruger9 wrote:


Maybe coincidentally?..... I was only able to get the tubes to within 4ma of each other... not sure how close they are supposed to be? When I set bias at 23 that was the high tube... the other one was at 19.


4 to 8 ma is good , better than 0 ma
Bias without knowing B+ voltage is a 1/2 job done . But 23 ma is not too hot .

Something wrong in the amp or tubes or you do some mistake


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Post subject: Re: custom vibrolux issue
Posted: Sun Jan 05, 2014 3:29 pm
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Yeah it's on both channels. I'll try swapping v6

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