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Post subject: Super-Sonic 112 Combo noise
Posted: Sun Aug 28, 2011 10:40 am
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I purchased a new 112 Combo Blond a few years back. It started making crackling noises and static like sounds while just sitting there. Took it back to the music store where I purchased it and they tracked it down to one of the tubes. After they replaced the tube it was fine. Now I am back to the same situation again and I am wondering if there is some newer tubes that I should try or should i get just get the same type that are in there now? Any help would be appreciated. Thanks Dave


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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Sun Aug 28, 2011 11:13 am
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Which amp is your combo 112 ? I'd like to find the schematic. And wich tube the store replace ? Power tube maybe ?
If they don't check and reajust bias with the new power tube , and guess they don't, all new tube will blow.
For next repair try to find a real good tube amp tech not a "nobody " in guitar store.


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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Sun Aug 28, 2011 11:28 am
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stratele52 wrote:
For next repair try to find a real good tube amp tech not a "nobody " in guitar store.


+1

Arjay

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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Sun Aug 28, 2011 1:35 pm
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I believe they replaced one of the 6L6GC tubes. Not 100% positive on that but it was one right at the back of amp. And no they didn't bias anything. They just took one out and put another one in. I have my owner's manual on the amp but it doesn't have the schematic in it. I guess I need to find someone who knows what there doing. Thanks


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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Sun Aug 28, 2011 4:07 pm
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I think that this is the schematic for the 112.

http://support.fender.com/schematics/guitar_amplifiers/Super-Sonic_Combo_schematic.pdf

From your description of the crackling static, and that the shop only replaced one tube, I would expect that a preamp tube was replaced, not requiring a bias adjust (preamp tubes [12AX7], reverb and pi tubes [12AT7] all counted as "preamp" tubes). The 6L6GCs will be the output tubes, big tubes, while the preamp are the small tubes. The preamp tubes are the usual suspects for this type of noise. It might be the same tube position, or one of the other positions this time. You might have to do some research into the qualities of different brands/types of preamp tubes, and see how much you want to spend. TheTubeStore has some great info on tubes, and some great reviews and comparisons. You could get one 12AX7 and one 12AT7 and try the new tubes in each position to see if a new tube cures the noise. For example, try a new 12AX7 in V1, if the noise is still present, put the original tube back in V1 and then try V2, etc, until the noise is gone. Check the tube chart in the amp for tube locations. Make sure to use a 12AT7 for the reverb (V9) and pi (V6). Make sure to turn the amp off before swapping tubes. It is possible that an output tube was replaced, I just think that it was more likely a preamp tube.

12AX7 preamp tubes:
http://thetubestore.com/12ax7review.html

12AT7 reverb and pi tubes:
http://thetubestore.com/12at7types.html

6L6 output tubes:
http://thetubestore.com/6l6templeton.html
and
http://thetubestore.com/6l6costello.html

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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Mon Aug 29, 2011 5:56 pm
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Thanks, This gives me some direction on where to go. And how to get there. :) I have the sticker that was inside the amp that gives the tube layout. It is showing the 12AT7's but it is showing the the other as a 12AX7WC. Does the WC matter?


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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Mon Aug 29, 2011 6:29 pm
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If this is referring to the Sovtek 12AX7WC, the WC is a newer version with a little more gain than the previous WA or WB. The difference is as with many types of preamp tubes, a different tube will have a different affect on the tone. I have found that the WC can give a better driven sound, whereas the WA is better for a clean sound. Sticking with the same tube is just to insure that you keep the same sound that you have now. Of course you can use any type of 12AX7 that you want to get the sound that you want, don't feel limited to a WC, or a Sovtek, there are many great brands for different tones. You can also try some lower gain tubes, such as 5751, 12AT7. It is typically best to stick with the 12AT7 for the reverb and pi. :idea:

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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Tue Aug 30, 2011 4:40 pm
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All this info is greatly appreciated. I guess the only other question I would have is, if I change the type of tube, do I replace all of them with the same type? Common sense tells me I should. Thanks Again Dave


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Post subject: Re: Super-Sonic 112 Combo noise
Posted: Tue Aug 30, 2011 7:22 pm
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You can mix and match the preamp tubes, no need to change all, you can only change one or two if you want. Some might like sound of a 12AX7-C in V1 and a JAN Phillips 12AT7 in V2, or vice-versa. Many combinations are possible, some tube positions will affect the drive channel, some will affect the clean channel, some will affect both channels. If you can follow the schematic, you can see which tube positions are in which channel in the circuit. The only thing to really remember is the reverb driver and pi tubes should be a 12AT7, any brand is OK. It is also best to make sure that the pi is balanced. Balanced tubes are also explained on the site, the other positions balanced is not required. If you change the output tubes, both should be changed at once with a matched set. :idea:

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