#1
I've been noticing for the last few days that my amp seems to be losing tone as I play through at practice. The volume isn't decreasing, but the gain gets lower. The power tubes are JJ KT77s that I put in about a year ago. The preamp tubes were in there when I bought it used a few years back and are probably about 4 years old. They're some crap Chinese tubes.

Since its a gain problem I'm thinking its the preamp tubes as opposed to the power tubes. Thouhgts?

Thanks.
-Joe
#3
Preamp tubes VERY rarely go out. What kind of amp is it? Two channels?
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#4
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Do you have active pickups? The batteries might be running out xP!

very true.
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#5
Try other guitars on it ftw
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#6
I replace power tubes yearly and preamp tubes every 2 years, if it's used frequently. I'd replace them all.
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#7
Quote by DLrocket89
I replace power tubes yearly and preamp tubes every 2 years, if it's used frequently. I'd replace them all.


FALSE. Most preamp tubes should last the life of the amp. Vintage Fender amps still have the original 12AX7's. The only time you should change these is if you want to modify the tone of your amp or you are hearing microphonics (super high pitched whine that is on all the time) which is caused by faulty preamp tubes.

Power amp tubes are a little different. They can last anywhere from 6 months to 5 years depending on how often and more importantly how hot you run them. If you put everything on 11 and play 4 hours a day, they might not make a full year. If you amp never goes above practice level then I've had tubes last 6 years. Change these as you need to, when you start to think your amp sounds much thinner and shows a steady volume loss.
Suhr Custom, Flaxwood Rautia or Grosh Tele thru
HBE Medicine Bawl Wah
Analogman BiComp
Texas Two Step OD
Fulltone Ultimate Octave/Fuzz
Boss CE-2
TC Nova Delay
SLO-100, 65 London or Bogner Shiva
Ask me about any of this stuff!
#9
Quote by inkandlead
I've been noticing for the last few days that my amp seems to be losing tone as I play through at practice. The volume isn't decreasing, but the gain gets lower. The power tubes are JJ KT77s that I put in about a year ago. The preamp tubes were in there when I bought it used a few years back and are probably about 4 years old. They're some crap Chinese tubes.

Since its a gain problem I'm thinking its the preamp tubes as opposed to the power tubes. Thouhgts?

Thanks.
-Joe
Real simple, imho. If you think it's likely to be the preamp tubes, replace them with something decent. Even if that doesn't fix the problem, you'll have decent preamp tubes when you DO find and fix the problem. Replacing crap Chinese tubes won't be money wasted.

What is "my amp"? Are KT77s standard, or did you replace another type with them? Did you rebias the amp for them? What idle current are you running through them?
Meadows
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#10
Quote by handlerb
FALSE. Most preamp tubes should last the life of the amp. Vintage Fender amps still have the original 12AX7's. The only time you should change these is if you want to modify the tone of your amp or you are hearing microphonics (super high pitched whine that is on all the time) which is caused by faulty preamp tubes.



I disagree 100% with you. If the amp is a head, it has a chance for preamp tubes to last longer, but if it's a combo the tubes are pretty much dead in two years because of speaker vibrations coupled to the tubes through the cabinet.

If you set the head on the speaker cab, the head isn't a lot better.

Your comment about older preamp tubes lasting longer is fine, except that, well "they don't make them like they used to". And knowing that his preamp tubes are "crap chinese" tubes, they're probably not built to the best quality anyways.

Why do you think the old Telefunken tubes are so prized? It's because they last a long time. If they're prized because they last a long time, it could be supposed that other tubes don't last a long time. Meaning, THEY NEED TO BE CHANGED EVERY NOW AND AGAIN.

Of course, if you're talking a cheapo Bugera or something, of course the tube will last the life of the amp. That'll be about 6 months.
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#11
Hey. Thanks for the quick responses. I'll try and get to all the looming questions...
Its a SoCal 50 that I did rebias to handle the 77s. I use it regularly. I noticed the problem the most with my Tele. I then switched to my SG and it seemed better however when I plugged in the SG I also dropped it to 25 watts instead of 50.
I'm planning on changing the preamp tubes anyway but there are 5 of them in this stupid thing!
None of my guitars have active pickups.

Also, for about a year I've been getting most of my gain from a pedal but recently just started using the amp gain so I'm not sure if its something that was wrong in the first place that I just never noticed due to lack of use.
Its a 2 channel amp but I would always use the dirty channel with the gain set low.
#12
Quote by DLrocket89
I disagree 100% with you. If the amp is a head, it has a chance for preamp tubes to last longer, but if it's a combo the tubes are pretty much dead in two years because of speaker vibrations coupled to the tubes through the cabinet.

If you set the head on the speaker cab, the head isn't a lot better.

Your comment about older preamp tubes lasting longer is fine, except that, well "they don't make them like they used to". And knowing that his preamp tubes are "crap chinese" tubes, they're probably not built to the best quality anyways.

Why do you think the old Telefunken tubes are so prized? It's because they last a long time. If they're prized because they last a long time, it could be supposed that other tubes don't last a long time. Meaning, THEY NEED TO BE CHANGED EVERY NOW AND AGAIN.

Of course, if you're talking a cheapo Bugera or something, of course the tube will last the life of the amp. That'll be about 6 months.
The additional details explain a lot.

I'm now wondering why there are even poorly-made preamp tubes when the technology is so old/straightforward and manufacturing capabilities have improved in so many areas. How much more would the better materials add on to the total cost for these "cheap" tubes?

I imagine that with China becoming a power house in manufacturing, some Chinese businessman would have reverse-engineered those prized Telefunken and other preferred tubes!