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Post subject: Help With My New '59 Bassman LTD
Posted: Fri Feb 14, 2014 9:40 pm
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Just got this amp today from Sweetwater, tried it out tonight with my Strat and after playing for a few minutes I noticed a low sounding ghost note when ever I let some of the lower notes ring. Kinda sounds like an octave pedal effect with a note an octave lower than the one you're playing, cuts off about 3/4ths of the way through the sustained note. Could this be tube related? Any help is very much appreciated, thanks.

G


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Fri Feb 14, 2014 11:35 pm
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Sounds like a microphonic tube. But it also might be a loose screw or two holding one or more of the speakers to the baffle board, or the baffle board itself loose from the cabinet. Try snugging all the fasteners down, including those that secure the chassis to the cabinet. Speakers screws should only be tightened a quarter turn beyond finger-tight.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Sat Feb 15, 2014 9:42 am
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I would call Sweetwater if you just got they should take care of it.


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Sun Feb 16, 2014 3:23 pm
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The tube label calls for a 12AX7 in V1, V2 and V3 but upon looking at them, I noticed that V3 is a 12AT7, is this tube ok in V3 or could this be what's causing the octave effect? This amp came factory sealed and had never been opened until I received it, but I can't understand why Fender would put a 12AT7 where a 12AX7 is supposed to go.

Thanks for all the help guys, G.


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Sun Feb 16, 2014 4:03 pm
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The 12AT7 is a lower-gain dual triode but draws significantly more current than the specified 12AX7 that should be used in the phase-inverter stage. No way to determine if that's the root cause of your "ghost" notes but I would install a 12AX7 at the V3 position to rule that out. The original 5F6-A tube array called for a 12AY7 in the V1 socket -- you might also try that out as well.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Sun Feb 16, 2014 6:47 pm
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Thanks Arjay, I tightened all the screws down, hopefully the 12AT7 didn't hurt the amp. Got some new tubes on the way and I'm gonna wait until I get them in before I play it again, gonna put a whole new set of tubes in and set the bias and go from there, hopefully she'll be good to go.

Thanks again for the help, G.


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Sun Feb 16, 2014 8:40 pm
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I had an original blackplate RCA 6V6 GTA in my '65 Princeton Reverb cause the exact same symptoms as yours (it about broke my heart to have to retire the pair and replace them). Hopefully the new tubes will cure your Bassman. One dialed in, they're great sonic platforms for just about any genre of music. Best of luck and keep us in the loop.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Fri Feb 21, 2014 11:26 am
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Glad to report all is well my Bassman, although I'm not sure exactly what the problem was seeing as how instead of performing one task and then testing, I performed several different things all one after the other and then tested, she now sounds amazing.

I know for sure it wasn't the guitar cable, but during setup of my Strat, I noticed the pickups were a little on the high side. Also while changing the tubes in my amp and setting the bias, I noticed it was way low, around 18 mA. I'm didn't check the bias on the power tubes that originally came in the amp, but if the was that low on them, I'm kinda thinking that may have been it.

Anyway, all is good and that's all that matters, I love this amp, G.


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Post subject: Re: Help With My New '59 Bassman LTD
Posted: Fri Feb 21, 2014 11:37 am
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18mA is way low for a pair of 6L6GC's in class AB operation.

Glad you got the amp perked up now!

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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