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Post subject: Reverb in Twin Reverb RI Wonky!?
Posted: Mon Jun 22, 2009 7:23 pm
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Hi guys! I have a new-to-me Twin Reverb RI. It's only 1 year old. I used it to practice with my band and I was well impressed. I didn't even mic it and it cut right through the mix. But alas, there is always a problem isn't there?

When I am about volume level 4 or 5 and in the reverb channel, instead of having a nice clean reverb, it kinda sounds like static, especially if I quickly mute the note. The staticky sound will continue the length of what should just be clean reverb.

Now, understanding that I know nothing about tube amps (normal stage amp - Line6 Spider III 150w ss), it sounds like maybe the reverb tube is microphonic. But I don't know which one it is. I tap on all of them with a pencil and no microphony at all. It may only do it with high volume levels though, since the reverb is clean below 4.

Does anyone know which of the 6 tubes in the back it is, so that I can check it out, I'm a little hesitant to pull tubes without knowing which is which. Could it be anything else?

Your opinions are greatly appreciated!!!!


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Posted: Thu Jun 25, 2009 2:13 pm
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Wow. So many views and no opinions?


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Posted: Thu Jun 25, 2009 3:13 pm
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Last edited by tinker tech on Wed Jul 29, 2009 11:00 am, edited 1 time in total.

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Posted: Wed Jul 01, 2009 4:31 pm
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I'd check the tank to see if a spring is off. Should be a 12at7 tube.


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Posted: Fri Jul 10, 2009 4:56 pm
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Yes, it should be a 12AT7 tube. A 12AX7 will work, but has much more gain. It sounds to me like maybe there's a 12AX7 where there should be a 12AT7? I know you've had another issue with some tubes; did you happen to put one back in the wrong place accidentally?

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Post subject: Twin Reverb
Posted: Fri Jul 10, 2009 6:18 pm
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Hi, There are three tubes ,V2 12AX7, V3 12AT7, V4 12AX7, that have the most influence on the reverb signal(before the power amp). How does the amp react on the normal channel? How about the vib. channel with the reverb switched off? Any noise generated by V2 will be amplified by V4 whether the reverb is on or off, the same for V1, the signal passes through half of V4 all the time. Art


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Posted: Fri Jul 10, 2009 6:27 pm
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Hi. Better late than never right? Well I changed one 12ax7 and alot of the problems calmed down. Clean channel works well. Reverb channel has good reverb now, but if I set the intensity knob on anything but one I can here it cycling. Very annoying.

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Posted: Fri Jul 10, 2009 7:37 pm
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Yeah , that's cool. Which 12AX7 did you R&R,V2 or V4? Cycling? You may hear a rushing sound when the reverb is turned up, but it should just be a smooth (white noise) sound in the background. It's just amplifying any noise created by the pre amp section. The only thing that cycles or oscillates in that amp is the vibrato section, and this will usually be heard as a tick, that will change with the speed and intensity controls. Art


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Posted: Fri Jul 10, 2009 8:28 pm
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V1, V2, V3. All greek to me. I really know nothing about that. If your looking at the back of the amp and you start counting the preamp tubes, it is the 4th one. As far as the noise, it's a pop pop pop that matches whatever you set the intensity at.Fairly loud too, not blow your speakers loud, but loud enough to notice it clearly.

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Post subject: Twin Reverb
Posted: Sat Jul 11, 2009 7:15 pm
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Oh, the V1,V2,etc. is just how vacuum tubes(valves) are shown on some schematics and tube charts,and the numbering usually begins on the right, as viewed from the rear of the chassis. But it is really up to the person drawing the schematics and layout(some amps don't have the tubes in one straight line). Anyway, you swapped out V4 and that fixed the problem, right? The Vib. tick would usually require some resistor upgrades and possibly a minor mod to this circuit, neither of which are advisable if it would void your warranty! You could try lower gain 12AX7's in V2&V4, but this might dampen the tone too much for your liking. You could also have a tech disconnect the circuit at the intensity pot, but then you would have no Vib., and again the warranty concern. No easy fix for this Fender tick! Art


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