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Post subject: Twin break up
Posted: Tue Feb 02, 2010 11:35 am
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At what point should a twin reverb start to break up? I know they are supposed to be really clean amps but mine seems to break up what I feel is too early. The aprox settings I normally use are, input 1, vol 5 or 6, treb 5, mid 4, bass 5, verb 3, master 10 through tha vibrato channel. I could just have a tube issue but I've only used this amp for probably about a total of a year and all new tubes where put in when I bought it. The biasing is good too.

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Posted: Tue Feb 02, 2010 8:17 pm
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Hi M7b5, the amp breakup can be affected by quite a few factors. The speakers, tubes, and filter caps would be the most influential, in my opinion. Guess your amp is a SF Twin Reverb. I think you might want to try the amp without the master volume engaged, or at least backed down to 7. A Twin will also breakup earlier with humbuckers. I'm guessing that with the master set to 10 you're breaking the negative feedback loop. Art

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Posted: Tue Feb 02, 2010 9:39 pm
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Mine stays clean till I can't stand it. It's still seriously clean at 5. I always keep the Master Volume on 10. Mine's a 76 SF 100 watter with the pull boost. The pull boost is horrible so I just leave it pushed in. There are so many variables but something doesn't sound right. If your using a Humbucker equipped guitar use input #2. Could be a tube issue or like Art said filter caps.


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Posted: Wed Feb 03, 2010 12:08 am
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Yeah, my mistake about being able to switch the master volume in or out of the circuit, should've checked the schem. A quality matched phase inverter tube would be a good idea, especially if you're running the power section wide open. Art

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Posted: Wed Feb 03, 2010 2:16 pm
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I was using humbuckers at the time so that could be it. I'll back the master down a bit, try single coils and see what happens. Its a '74 by the way and it's had a bad output fixed, all 4 resistors replaced and rebuilt power supply. Thanks for the advice :)

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Posted: Wed Feb 03, 2010 7:40 pm
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Yeah, you should be able to leave the master all the way up and make any adjustments on the pre amp volume & tone controls. And of course, the guitar controls will have a greater effect at high volume. The speakers play a major role. and since the power and output secton seem to be in primo shape, I would think about what the speakers are doing. Art

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Posted: Thu Feb 04, 2010 9:51 am
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The single coils helped out alot. It doesn't break up as early. It does not have stock speakers tho. One was cracked so I replaced both with eminece ledgends which I have in a 2x12 cab hooked up to a Mesa/boogie. I know they are no JBL's but those were out of my price range.

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Posted: Fri Feb 05, 2010 8:09 am
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my 74 twin reverb, starts to break up after 5 on the volume. But as stated above caps, speakers, settings, etc.,. all come to play. great amps, heavy, but worth the tone. :)

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Posted: Fri Feb 05, 2010 8:48 am
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m7b5 wrote:
The single coils helped out alot. It doesn't break up as early. It does not have stock speakers tho. One was cracked so I replaced both with eminece ledgends which I have in a 2x12 cab hooked up to a Mesa/boogie. I know they are no JBL's but those were out of my price range.


That's probably the breakup right there. Thing is, if you like the tone, I wouldn't worry about it. Sometimes I wish my Twin could break up on it's own at lower volumes.


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Posted: Sun Feb 07, 2010 9:10 am
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On a twin, I believe you can pull two of the output tubes to lower overall volume; can't remember if its inside/outside pairs or pairs next to each other - hopefully Art or 63supro will chime in. Of course if you do that, you will lower your overall volume, but not the fabulous "gym in a box" weight Twins are known for.

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Posted: Mon Feb 08, 2010 9:34 pm
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Yeah, you can remove the two outside or two inside power tubes to halve the power output. But this also changes the impedance. The amp would want to see an 8ohm speaker load and the feedback loop should probably have the 100ohm resistor changed to 47ohms. Otherwise, the character of the power section would be changed. Of course, the bias would have to be checked. Art

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