I was playing this amp today, on about 3-4 on the volume. I was using my Catalinbread DLS mk 3 with the bass about halfway up. I hit a power chord and the amp seemed to "clip". Basically it cut out for a split second. I have never actually heard a tube amp do this before. It was an awful sound, something I would expect from hitting the front end of a solid state amp way too hard. I just picked this amp up used about 2 weeks ago. What do you guys think is wrong with it? If I turn the bass down on the DLS it doesn't do it, but obviously something is wrong
Help! Problem with Twin RI
- Thread starter nedcronin
- Start date
Chickenwings
Alnico 6/8
Re: Help! Problem with Twin RI
At this point its only guesswork, but it sounds like a tube is vibrating and shorting out. try giving all the tube sockets a spray with contact cleaner - spray the tube pins too and insert and remove them a couple times while its still wet. When the cleaner dries, plug em all back in a fire it up. See how that goes first.
If that doesn't sort it out, then turn your amp around and take off all the tube covers. Crank it as usual and play the same thing that is causing you this trouble...have a look and see if any of the tubes are glowing excessively.have a close look especially at the PI tube (the last one before the power tubes) - check that it is a 12aT7 and not a 12ax7 (a lot of people put 12ax7's in here to reduce headroom).
This is only a start in terms of troubleshooting, but this stuff is non-invasive and routine anyway.
At this point its only guesswork, but it sounds like a tube is vibrating and shorting out. try giving all the tube sockets a spray with contact cleaner - spray the tube pins too and insert and remove them a couple times while its still wet. When the cleaner dries, plug em all back in a fire it up. See how that goes first.
If that doesn't sort it out, then turn your amp around and take off all the tube covers. Crank it as usual and play the same thing that is causing you this trouble...have a look and see if any of the tubes are glowing excessively.have a close look especially at the PI tube (the last one before the power tubes) - check that it is a 12aT7 and not a 12ax7 (a lot of people put 12ax7's in here to reduce headroom).
This is only a start in terms of troubleshooting, but this stuff is non-invasive and routine anyway.
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Chickenwings
Alnico 6/8
Re: Help! Problem with Twin RI
I'm not sure how experienced you are with amps, but here is some useful stuff if its not something youve come across before:
with ANY tube amp where something goes wrong, always start with checking the tubes. These things are consumable items like tyres on a car and need regular checking and replacement.
When a light globe blows in your house, you don't need to call an electrician straight away...change the globe and go from there. Its the same with tube amps.
I'm not sure how experienced you are with amps, but here is some useful stuff if its not something youve come across before:
with ANY tube amp where something goes wrong, always start with checking the tubes. These things are consumable items like tyres on a car and need regular checking and replacement.
When a light globe blows in your house, you don't need to call an electrician straight away...change the globe and go from there. Its the same with tube amps.
Re: Help! Problem with Twin RI
Hey thanks. I do have a 12AX7 in the PI. Trying to tame the over brightness of this rig. It is an old Fender labeled tube but my buddy said it tested good. Could easily be the problem though. I'll swap some tubes around when I get home, I hope that puts a fix on it. Thanks again for all the help! BTW, I plan on ordering the Texas Heats for this amp too.
Hey thanks. I do have a 12AX7 in the PI. Trying to tame the over brightness of this rig. It is an old Fender labeled tube but my buddy said it tested good. Could easily be the problem though. I'll swap some tubes around when I get home, I hope that puts a fix on it. Thanks again for all the help! BTW, I plan on ordering the Texas Heats for this amp too.
Gearjoneser
Gear Ho
Re: Help! Problem with Twin RI
Are you sure it's not the speakers buckling under the volume and bass?
That's why I don't like low wattage speakers, particularly cheap special design types.
Some good Eminence or Celestion speakers handle lows a lot better. I really love the Emi Patriot Swamp Thang in my Fender Pro Reverb.
Are you sure it's not the speakers buckling under the volume and bass?
That's why I don't like low wattage speakers, particularly cheap special design types.
Some good Eminence or Celestion speakers handle lows a lot better. I really love the Emi Patriot Swamp Thang in my Fender Pro Reverb.
Chickenwings
Alnico 6/8
Re: Help! Problem with Twin RI
a 12at7 can handle roughly 10 times the voltage of a 12ax7.
Fender tubes are really sovtek 12ax7 wa models and wb models...the cheapest sovtek make. Pi tubes are the hardest working tube in an amp and they take a real hammering. Even if its not the problem, you should keep a 12at7 in there as per the design spec, and warm your amp up other ways ( i think your choice of texas heats is a perfect way to do it).
a 12at7 can handle roughly 10 times the voltage of a 12ax7.
Fender tubes are really sovtek 12ax7 wa models and wb models...the cheapest sovtek make. Pi tubes are the hardest working tube in an amp and they take a real hammering. Even if its not the problem, you should keep a 12at7 in there as per the design spec, and warm your amp up other ways ( i think your choice of texas heats is a perfect way to do it).
Re: Help! Problem with Twin RI
I put a 5751 and a fresh tube in the PI and it went away. The 5751 helped with the brightness I was fighting, but I think I will go with the Eminence Texas heats. If that isn't a dramatic improvement in more low end, more musical voicing and a warming of the shrill top end, I'm going to be bummed.
I put a 5751 and a fresh tube in the PI and it went away. The 5751 helped with the brightness I was fighting, but I think I will go with the Eminence Texas heats. If that isn't a dramatic improvement in more low end, more musical voicing and a warming of the shrill top end, I'm going to be bummed.
Chickenwings
Alnico 6/8
Re: Help! Problem with Twin RI
it will make a big difference fo sho...but there is one capacitor in the twins tone stack that scoops out a lot of mids which is part of the reasons these things are so clean sounding. If the speaker swap doesnt do it for you, then this will.
A super reverb has a .022uf cap coming off the bass pot which lets a lot more bass and low mids thru whereas the twin has a .047. Here is an idea of the difference in sound:
The green curve is the stock twin's tone curve with everything on 5, whereas the aqua one is with the .022uf cap.
This mod is only the few cents it costs for a capacitor. Easy to do if you are handy with a soldering iron, and reversible. If you like it, you can lave channel one stock and have different tones from the two channels.
it will make a big difference fo sho...but there is one capacitor in the twins tone stack that scoops out a lot of mids which is part of the reasons these things are so clean sounding. If the speaker swap doesnt do it for you, then this will.
A super reverb has a .022uf cap coming off the bass pot which lets a lot more bass and low mids thru whereas the twin has a .047. Here is an idea of the difference in sound:
The green curve is the stock twin's tone curve with everything on 5, whereas the aqua one is with the .022uf cap.
This mod is only the few cents it costs for a capacitor. Easy to do if you are handy with a soldering iron, and reversible. If you like it, you can lave channel one stock and have different tones from the two channels.
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