Ghost sound on my ac30. (seeking retube advice)
- Gw10101
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Ghost sound on my ac30. (seeking retube advice)
So i have this AC30cc2 that a friend of mine is wanting to take off my hands. All is well with the amp except for a slight mushy hissing sound that it makes ocasionally when certain frequencys are put through the it. (almost liike the crackle of a dirty pot being adjusted only we were not adjusting any settings on the amp) the sound also didnt appear till after the tubes had been warmed up for about ten minutes. the sound also didnt seem to appear till after certain frequencys were put through it. (it wasnt like a constant hum, or chronic crackle) also i use an extention cab, and it made that sound through the cab as well.
It isnt something that i had noticed before we got to gether to check the thing out. but now that i have noticed it i can't in good conscience sell it to him till i fix it.
I spoke to a few friends that are more learned than i on the topic of amp repair, and they thought for sure that it was one of preamp tubes going out. I also spoke with an amp repair shop locally that i trust, and they suggested that i swap out some 12ax7's and see if i get rid of the problem rather than spend the money haveing them do it for me (wich honestly is pretty decent of them to suggest given my money situation).
however, i have never traded out tubes on an amp before
so here are my questions for you.
have any of you ever re-tubed the preamps of an ac 30. is it just a matter of simply un plugging the tube and then plugging in the new one? i read somewhere about biasing tubes with a variac or something, but it seemed to relate to power tubes.
im useless when reading schematics, but i found some on the ac30cc2 in pdf, and it suggested that there were only 3, 12ax7a's in the amp. does it sound from my discription that one of these could be the problem? there are some other tubes aside from the power tubes (el-84's) that im un familliar with, and i would likely have to mail order to get if thats the case.
if not the tubes any other ideas as to what could be causing the problem?
i really do appriciate any advice you can throw in my directioin.
thanks
greg
It isnt something that i had noticed before we got to gether to check the thing out. but now that i have noticed it i can't in good conscience sell it to him till i fix it.
I spoke to a few friends that are more learned than i on the topic of amp repair, and they thought for sure that it was one of preamp tubes going out. I also spoke with an amp repair shop locally that i trust, and they suggested that i swap out some 12ax7's and see if i get rid of the problem rather than spend the money haveing them do it for me (wich honestly is pretty decent of them to suggest given my money situation).
however, i have never traded out tubes on an amp before
so here are my questions for you.
have any of you ever re-tubed the preamps of an ac 30. is it just a matter of simply un plugging the tube and then plugging in the new one? i read somewhere about biasing tubes with a variac or something, but it seemed to relate to power tubes.
im useless when reading schematics, but i found some on the ac30cc2 in pdf, and it suggested that there were only 3, 12ax7a's in the amp. does it sound from my discription that one of these could be the problem? there are some other tubes aside from the power tubes (el-84's) that im un familliar with, and i would likely have to mail order to get if thats the case.
if not the tubes any other ideas as to what could be causing the problem?
i really do appriciate any advice you can throw in my directioin.
thanks
greg
- Terry Wright
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Re: Ghost sound on my ac30. (seeking retube advice)
It could be a microphonic (noisy) preamp tube. You don't have to check or set bias on preamp tubes, just plug new ones in. Just buy one real good 12AX7 and try it in each position until the noise goes away. It could possibly be some other problem, but this is the easiest thing to try, and the most likely problem.
- pullover
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Re: Ghost sound on my ac30. (seeking retube advice)
Sometimes just re-seating the tubes works too. Just unplug them all while the amp is off and then plug them back in the exact same slot. Don't touch the tubes with your hands, use a clean rag or a t-shirt or something.
Why should we buy postage stamps? We can make our own.
- mewithoutus
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Re: Ghost sound on my ac30. (seeking retube advice)
that sounds like exactly what happened to me in my fender hot rod deluxe. certain frequencies caused a weird hum and hiss. i freaked cuz i thought the amp was broke, but it was just a microphonic tube!
for preamp tubes, just get a set of 12ax7's and swap them out.
for power tubes, you need to buy a matched set, and its a good idea to have them biased by a tech so that your amp is running at its best. ac30's are run pretty hot arent they?
for preamp tubes, just get a set of 12ax7's and swap them out.
for power tubes, you need to buy a matched set, and its a good idea to have them biased by a tech so that your amp is running at its best. ac30's are run pretty hot arent they?
=--->christopher
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myspace.com/foxestheband
- Gw10101
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Re: Ghost sound on my ac30. (seeking retube advice)
Hey guys
thanks, I am going to go get a few 12ax7's and try them out this weekend. hopefully that will do the job
cheers
greg
thanks, I am going to go get a few 12ax7's and try them out this weekend. hopefully that will do the job
cheers
greg
- fuzzjunkie
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Re: Ghost sound on my ac30. (seeking retube advice)
AC-30s don't need to be biased.
sleeping on a bed of fuzz and feedback
- gogothegogo
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Re: Ghost sound on my ac30. (seeking retube advice)
I've got similar hiss from my two tube amps - old 74' fender bassman 100 head, and new Peavey Classic 50 combo.
hiss appears from time to time and last for half a second.
I believe it's normal tube-shaking sound because both amps are on top of shaking cabs
hiss appears from time to time and last for half a second.
I believe it's normal tube-shaking sound because both amps are on top of shaking cabs
- Gw10101
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Re: Ghost sound on my ac30. (seeking retube advice)
cool, thanks for all the advice, today i finished my retube project.
sence the thing didnt need biasing i went to the guitar shop and bought 3 12ax7s and 4 el84s
then spent the hour dismantling the cabinet (you would tink this part of it would be easier!)
replaced the tubes, provided a speaker load, tested out and honestly, it sounds great! now if only i could get cash in hand for this thing befor my ebay item dissapears....
the clock is ticking
thanks again guys
greg
sence the thing didnt need biasing i went to the guitar shop and bought 3 12ax7s and 4 el84s
then spent the hour dismantling the cabinet (you would tink this part of it would be easier!)
replaced the tubes, provided a speaker load, tested out and honestly, it sounds great! now if only i could get cash in hand for this thing befor my ebay item dissapears....
the clock is ticking
thanks again guys
greg
- spaceghost
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Re: Ghost sound on my ac30. (seeking retube advice)
greg, you might make sure the power tubes don't need to be rebiased. i thought only the preamp tubes could be swapped without a rebi.Gw10101 wrote: cool, thanks for all the advice, today i finished my retube project.
sence the thing didnt need biasing i went to the guitar shop and bought 3 12ax7s and 4 el84s
- pullover
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Re: Ghost sound on my ac30. (seeking retube advice)
http://www.voxamps.co.uk/support/faqs.asp wrote:When changing power valves, always replace the whole set and never mix valves from different manufacturers. There is usually no bias adjustment on AC30s and AC15s.
Why should we buy postage stamps? We can make our own.
- spaceghost
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Re: Ghost sound on my ac30. (seeking retube advice)
touchépullover wrote:http://www.voxamps.co.uk/support/faqs.asp wrote:When changing power valves, always replace the whole set and never mix valves from different manufacturers. There is usually no bias adjustment on AC30s and AC15s.
- pullover
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Re: Ghost sound on my ac30. (seeking retube advice)
I was surprised by it, too! Apparently they are self-biasing. As long as you use a matched pair of tubes you should be fine.
Why should we buy postage stamps? We can make our own.
- Gw10101
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Re: Ghost sound on my ac30. (seeking retube advice)
No one was more suprised than me.
I replaced the 12ax7's and it basically fixed the problem, but sence im selling the thing (to a mutual friend of mine and spaceghost's actually) i wanted to make sure. so sunday morning i sat there playing in every concievable knob setting i could do, and also every setting on the guitars that i had on hand. and if i set the amp loud and the guitar soft i could still hear a little fizzing sound underneath what i was playing, so i called GC and got 4 el84's (matched set) and droped them in. and now nothing i do makes the problem happen.
so yeah i was amazed that they were self biasing.
i used to have a 30 watt gibson ga-30 (really cool amp if you can find them, 1x12 and 1x10 class a) it was also self biasing.
but thankfully it was. because i would still be trying to figure it out if it werent.
(and DNL, the amp i think is going to Danny of T. Dali i think it will work well for them)
cheers
greg
I replaced the 12ax7's and it basically fixed the problem, but sence im selling the thing (to a mutual friend of mine and spaceghost's actually) i wanted to make sure. so sunday morning i sat there playing in every concievable knob setting i could do, and also every setting on the guitars that i had on hand. and if i set the amp loud and the guitar soft i could still hear a little fizzing sound underneath what i was playing, so i called GC and got 4 el84's (matched set) and droped them in. and now nothing i do makes the problem happen.
so yeah i was amazed that they were self biasing.
i used to have a 30 watt gibson ga-30 (really cool amp if you can find them, 1x12 and 1x10 class a) it was also self biasing.
but thankfully it was. because i would still be trying to figure it out if it werent.
(and DNL, the amp i think is going to Danny of T. Dali i think it will work well for them)
cheers
greg
- spaceghost
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Re: Ghost sound on my ac30. (seeking retube advice)
yes t'will yes t'will.Gw10101 wrote: the amp i think is going to Danny of T. Dali i think it will work well for them)
- Gw10101
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Re: Ghost sound on my ac30. (seeking retube advice)
I also wanted to say that retubeing that amp was way cheaper than i had thought it would be, i think i paid 65 dollars for all 7 tubes that i replaced.
greg
greg