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-   -   Amp Issues? (http://www.ultimate-guitar.com/forum/showthread.php?t=1566340)

Mohican 10-05-2012 02:58 AM

Amp Issues?
 
So I was playing guitar today through my Fender Hot Rod III. I bought it new back in 2011 and it hasn't ever really been "cranked". The knob goes up to 12, but the highest it's been is maybe 5 or so, but that was to wake up a stubborn roommate. I typically play it on 3 or so. Anyway, here is my issue:
While I was warming up and doing a sound check today, my amp "fluttered" when I played a low note. It was a weird sound, not really distorted, but not clean or normal sounding and it only happened when I played a low E. I checked the wires, I played hooked up to the amp straight from guitar, I had a buddy play his guitar through my amp and the noise persisted. However, after warm up, I turned it off as we went to get ready and when I turned it back on, the sound had gone away.
I've had a blown subwoofer before and the sound was similar to that, but not nearly as bad. My initial thought is a blown (or partially blown) speaker. Anyone else with any other ideas?

red.guitar 10-05-2012 09:39 AM

How old are your tubes? I'm in no way a tube expert, but to me, it sounds like a worn tube, or maybe the microphopnics may be off in a power tube??

Someone who knows a little more about tubes may be able to help you better!

GABarrie 10-05-2012 09:54 AM

sounds like you need a re-tube. have you ever had new tubes put in it or still using the stock ones?

Mohican 10-05-2012 05:47 PM

I'm still using the stock ones. They should be changed 6 months, right? I've had a few different amps and each one has had different needs. I've owned a Fender from 72 with the original vacuum tubes.

ne14t 10-05-2012 06:07 PM

Tube's are a weird beast, I find if I leave my Marshall Haze on for a long period of time 8+ hours it will start to get a bit of a crackle on the clean channel, my Tubemeister 5 does not exhibit this problem so I started the mad hunt on tube info for my Marshall. It got to the point where I was reading manufacturer data sheets and stuff to quell my need for info, I ended up stumbling across a scientists little blurb on tubes where they were talking about how the electrons can randomly migrate between the plates inside the tube causing unwanted effects and this was generally when the tube was about to crap out or after extremely prolonged use, the heat would cause it to happen more. I wish I could explain it more but I am FAR from a professional when it comes to electronics, I just pretend to be one!

Anyways with more research I found with my Marshall it tended to be the V1 preamp tube that would get finnicky, one guy suggested I try tapping on the tube lightly with the rubber eraser of a pencil while the tube was on and another suggested I remove the back panel of the amp for better airflow to cool the tubes. Did both its been 8 months and I havent heard a single crackle and the amp has been on for over 24 hours constantly at some points. This amp does not have a standby either which is really a tube saver, it will put enough voltage through to keep the tubes "warm" but not enough to cause decreased life.

Tubes are like a light bulb, they can essentially run forever it all really depends on the demand put on them, unfortunately amps are pretty demanding. The more time the amp spends on and the more you play it cranked the sooner you will have to replace the tubes my Marshall is 2 years old and has not had a re-tube still the factory chinese tubes, did need a rebiasing though which also really helped, hate to admit it but it was running about 50% too cold and it really made a difference when I corrected that.

TLDR: Yes OP I would get some spare tubes on hand if you don't already it sounds like one somewhere in the chain is dying.

LaidBack 10-05-2012 06:14 PM

I had a fluttering noise with my Mesa. Looking back, it sounded a LOT like the sound when they engaged the sleep machines from the movie Inception :haha Turns out it was a microphonic tube. Just buy some new preamp tubes. A sure way to check is to tap on each preamp tube with the eraser of a pencil while the amp is on.

Be careful in there, though.

ne14t 10-05-2012 06:24 PM

Quote:
Originally Posted by LaidBack
I had a fluttering noise with my Mesa. Looking back, it sounded a LOT like the sound when they engaged the sleep machines from the movie Inception :haha Turns out it was a microphonic tube. Just buy some new preamp tubes. A sure way to check is to tap on each preamp tube with the eraser of a pencil while the amp is on.

Be careful in there, though
.


Both bold are good info, high watt combo amps can be susceptible to microphonics more because the amp chassis is generally exposing inside the speaker cab. I remember reading this about the 40 watt version of the Haze as it was a combo. I have the 15 watt head, which fills in point # 2 in bold, I think my 15 watt amp was running something stupid like 400 or 500 volts at the transformers certainly want to be careful around that. The higher wattage the head the more power it will have running through it.

Kevin Saale 10-05-2012 06:25 PM

Quote:
Originally Posted by ne14t
Tube's are a weird beast, I find if I leave my Marshall Haze on for a long period of time 8+ hours it will start to get a bit of a crackle on the clean channel, my Tubemeister 5 does not exhibit this problem so I started the mad hunt on tube info for my Marshall. It got to the point where I was reading manufacturer data sheets and stuff to quell my need for info, I ended up stumbling across a scientists little blurb on tubes where they were talking about how the electrons can randomly migrate between the plates inside the tube causing unwanted effects and this was generally when the tube was about to crap out or after extremely prolonged use, the heat would cause it to happen more. I wish I could explain it more but I am FAR from a professional when it comes to electronics, I just pretend to be one!

Anyways with more research I found with my Marshall it tended to be the V1 preamp tube that would get finnicky, one guy suggested I try tapping on the tube lightly with the rubber eraser of a pencil while the tube was on and another suggested I remove the back panel of the amp for better airflow to cool the tubes. Did both its been 8 months and I havent heard a single crackle and the amp has been on for over 24 hours constantly at some points. This amp does not have a standby either which is really a tube saver, it will put enough voltage through to keep the tubes "warm" but not enough to cause decreased life.

Tubes are like a light bulb, they can essentially run forever it all really depends on the demand put on them, unfortunately amps are pretty demanding. The more time the amp spends on and the more you play it cranked the sooner you will have to replace the tubes my Marshall is 2 years old and has not had a re-tube still the factory chinese tubes, did need a rebiasing though which also really helped, hate to admit it but it was running about 50% too cold and it really made a difference when I corrected that.

TLDR: Yes OP I would get some spare tubes on hand if you don't already it sounds like one somewhere in the chain is dying.


Leaving your amp in standby for an extended period is not advisable though. That will damage your tubes as well.

ne14t 10-05-2012 06:36 PM

Oh yeah not advisable at all, most of the time for me it was burnt out recording sessions or whatnot where I passed out got up the next morning it was still on so I just went back to playing. But right back to the light bulb comparison, the more and longer its on the shorter it will last in the long run.

Funny side story, I vaguely remember reading somewhere that Jimi Hendrix used to have his amps on all the time, they would be unplugged to be taken from the truck to the stage and then back to the truck otherwise they were on all the time.

Mohican 10-06-2012 03:39 PM

Great info. I will definitely check my tubes out then. Like I said, most of my amps have not had the specific issue I'm having now. The 72 that I had had a broken reverb spring that made a similar sound, but upon listening to it closer, I ruled that option out. Thanks for all the help.


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