Members dogman Posted January 8, 2008 Members Share Posted January 8, 2008 I am having problems with a couple of my amps..70's era Ampeg SVT(wierd noises) and I recorded the noises with Cool Edit Pro and wanted to host them somewhere(they are small files) so that I could ask for help here and from others. But I can't seem to find a way to upload MP3s easily and for free. Where can I easily upload small wav. or mp3 files to and have them hosted so that I can link them for others to hear and help out with?: Link to comment Share on other sites More sharing options...
Members jackcheez Posted January 8, 2008 Members Share Posted January 8, 2008 You can attach MP3s to a post right here. Link to comment Share on other sites More sharing options...
Members dogman Posted January 8, 2008 Author Members Share Posted January 8, 2008 You can attach MP3s to a post right here. really? Ok,Ill post it in the post following this one describing the noise problem, here it goes. The amp is a mid 70's Ampeg SVT head and the noise seems to come in out of nowhere at intermittent times. However, when it does it, it is usually almost like a feedback note with a highend noise(might be tubes, not sure if its that or not or whether its preamp or power tubes. Please ignore my {censored}ty playing as I was just noodling on an old ZZ top song and my sound is way better than this file makes it sound(it was a crappy headphone microphone I used to pick up the sound and it was farting out(couldnt handle the lowend) ANy help would be most appreciated. Could it be filter caps, or dirty pots or would it sound to you more like preamp or output tubes? By the way, I am using the Channel one side of the amp(with the midrange control) and I am plugged into the bright one input. I dont use the channel two and never have since I bought it since it has no midrange control plus it has a nasty thump when you touch or turn the low knob. We are going to be gigging in a few weeks and this is crappy timing for amp problems. Link to comment Share on other sites More sharing options...
Members jackcheez Posted January 8, 2008 Members Share Posted January 8, 2008 Are you attaching the file ? Sometimes it takes a few tries. Link to comment Share on other sites More sharing options...
Members Super Bass Posted January 8, 2008 Members Share Posted January 8, 2008 http://hc.bloodyvelvet.com You can attach them there. Link to comment Share on other sites More sharing options...
Members dogman Posted January 8, 2008 Author Members Share Posted January 8, 2008 heres the sound: Link to comment Share on other sites More sharing options...
Members D Aussie Posted January 8, 2008 Members Share Posted January 8, 2008 I know it isnt appropriate at all times, but that is one damn cool noise!You could sell that as a sample.I have no idea what it is, tho. Link to comment Share on other sites More sharing options...
Members guitargod0dmw Posted January 8, 2008 Members Share Posted January 8, 2008 It almost sounds like microphonics. When was the last time you had your tubes changed & biased? Check this page out and see if it helps you at all...particularly from "Tube noise' down... http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html Link to comment Share on other sites More sharing options...
Members dogman Posted January 8, 2008 Author Members Share Posted January 8, 2008 I know it isnt appropriate at all times, but that is one damn cool noise! You could sell that as a sample. I have no idea what it is, tho. Ha, thanks D Aussie, I guess:p If it was something I was shooting for, it could be kind of cool, but this {censored} is uncontorllable and comes and goes and the most inopportune times. I really need to find the root of this problem soon so anyone out there that has amp experience with this, I could really use your help! Link to comment Share on other sites More sharing options...
Members jackcheez Posted January 8, 2008 Members Share Posted January 8, 2008 Here's another good reference. http://www.geofex.com/ampdbug/ampdebug.htm Link to comment Share on other sites More sharing options...
Members misterhinkydink Posted January 8, 2008 Members Share Posted January 8, 2008 heres the sound: It's difficult to hear on my notebook but my first guess would be a microphonic tube. I'd first try re-seating them. If that doesn't help try tapping them with a pencil. All will make some noise but one or more will be much louder it they're a problem. When I get home I'll listen on better equipment. Link to comment Share on other sites More sharing options...
Members dogman Posted January 8, 2008 Author Members Share Posted January 8, 2008 It almost sounds like microphonics. When was the last time you had your tubes changed & biased? Check this page out and see if it helps you at all...particularly from "Tube noise' down... http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html thats the thing, I actually brough it into a local music store about 6 months ago to have it served(check caps, tubes, etc..) the guy who works on them Ive known for a long time and does know his stuff. But he told me after cleaning it up, the inside was really dirty, and he cleaned and tightend all of the tube sockets and checked the tolerances on the caps, they were okay. He said he checked the tubes as well and that they wer allright as well. However, this sound usually happens mostly when playing at loud(gig) levels and I doubt or at least dont think that the guy cranked it in his little workshop while testing it out. COuld be a bad tube that didnt show up because the volume was too low? Think its output or preamp? Also, I bought this amp used about 2 years ago, and the tubes that are in it are the same ones that are still in it, Ive not changed any of them. Looking into the back of the amp, the outputs (at least 4 of them for sure) have been changed in the past, though I dont know how long ago. WHat now guys? Link to comment Share on other sites More sharing options...
Members jackcheez Posted January 8, 2008 Members Share Posted January 8, 2008 It's difficult to hear on my notebook but my first guess would be a microphonic tube. I'd first try re-seating them. If that doesn't help try tapping them with a pencil. All will make some noise but one or more will be much louder it they're a problem. When I get home I'll listen on better equipment. I'd start with the preamp tubes. Link to comment Share on other sites More sharing options...
Members misterhinkydink Posted January 8, 2008 Members Share Posted January 8, 2008 I'd start with the preamp tubes. Yes, I should have specified that. I doubt it's a 6550 problem. Link to comment Share on other sites More sharing options...
Members SelenaBassGirl Posted January 9, 2008 Members Share Posted January 9, 2008 mine is driving me nuts too..I have to take a wrench and tighten the part the bass cord plugs in b/c it makes a terrible loud humming sound sometimes. Esp if I turn it up loud. Or after a few plays, it vibrates loose and makes that sound. Link to comment Share on other sites More sharing options...
Members Guttermouth Posted January 9, 2008 Members Share Posted January 9, 2008 i'm betting bad preamp tube (or socket),loose ground or bad solder joint on the board somewhere ( in that order). Link to comment Share on other sites More sharing options...
Members tylytle Posted January 9, 2008 Members Share Posted January 9, 2008 I am guessing preamp tube also. Link to comment Share on other sites More sharing options...
Members dogman Posted January 9, 2008 Author Members Share Posted January 9, 2008 okay, thanks guys. Ill start out by changing all of the preamp tubes first(damn, there's alot of 'em in there too!!(not all of them or 12ax7 either, some others in there as well) Ill let yall know when I get them changed and if it made a difference or not. Appreciate the help!! Link to comment Share on other sites More sharing options...
Members misterhinkydink Posted January 9, 2008 Members Share Posted January 9, 2008 okay, thanks guys. Ill start out by changing all of the preamp tubes first(damn, there's alot of 'em in there too!!(not all of them or 12ax7 either, some others in there as well) Ill let yall know when I get them changed and if it made a difference or not. Appreciate the help!! Channel #1 should be 3 12DW7s and a 6C4, channel #2 is a 12AX7. Before doing anything, make sure to check that a tube shield isn't vibrating against its tube. No point in replacing a good 12DW7 as they're not cheap. Link to comment Share on other sites More sharing options...
Members dogman Posted January 9, 2008 Author Members Share Posted January 9, 2008 Channel #1 should be 3 12DW7s and a 6C4, channel #2 is a 12AX7. Before doing anything, make sure to check that a tube shield isn't vibrating against its tube. No point in replacing a good 12DW7 as they're not cheap. thanks for the info misterhinkydink(BTW, what do you mean by a tube shield? Are you referring to the small metal covers sometimes seen over preamp tubes? If so, then I gotcha:thu: and if not, then please elaborate a little. Thanks man! Link to comment Share on other sites More sharing options...
Members bassesofalessergod Posted January 9, 2008 Members Share Posted January 9, 2008 microphonics for sure!!! Link to comment Share on other sites More sharing options...
Members dogman Posted February 22, 2008 Author Members Share Posted February 22, 2008 OK, update on the SVT,I took the back off of it to check it out and see if I could locate the culprite microphonic tube. Tried cranking it to about 1 o' clock volume and tapping the tubes(power and preamp) with pencil eraser but none of them would ring out a noise like what I was hearing before or even noticably(I know all tubes are somewhat microphonc to some degree but I was hearing nothing noisiy here)Ive made up my mind Im just gonna change all of the preamp tubes first and see what happens. BUT.....The BIG surprise was win I unplugged and reseated the preamp and driver tubes in that I found many of them were WRONG! In fact all 4 of the sockets that are suppose to have a 12DW7 in them have instead 12ax7 and GT 7025 tubes in them!(In the preamp section,V1 has a GT7025,V3 has a 12ax7,& V4 has a GT 7025 as well) and in the power section where V1 is suppose to be a 12DW7 there is a 12ax7A in there too! I did look on quite a few forums after this to see if this was detrimental or dangerous to the amp and couldnt find anything. However I did see mentioned that at one time a book by a guy named Aspen Pittman on svt tube conversion came out showing how to convert the SVT amps to use 12ax7 tubes instead of DW7 tubes(Ill assume this was when DW7's were very scarce) but I dont know if this amp was modifiend to do this or if someone just stuck 12ax7 tubes in place of the DW7's . IF the conversion was done on it, is it safe to switch it back to 12DW7's again or must I have it checked out (yet again?!) before doing so? Also, I do remember reading somewhere online (and sadly I cant find it now after looking for almost a hour:confused:) that either the 12DW7 tubes or (more likely) the 12BH7 tubes must be re-biased too, just like the output tubes on this amp. Does anyone know for a fact that it is just the BH7 tubes and output 6550s, OR do those wierd 12DW7 tubes require biasing too? Link to comment Share on other sites More sharing options...
Members Mudbass Posted February 22, 2008 Members Share Posted February 22, 2008 It sounds like a tube or a valve. If you're British check the valves, if you're American check the tubes. Link to comment Share on other sites More sharing options...
Members misterhinkydink Posted February 22, 2008 Members Share Posted February 22, 2008 .....The BIG surprise was win I unplugged and reseated the preamp and driver tubes in that I found many of them were WRONG! In fact all 4 of the sockets that are suppose to have a 12DW7 in them have instead 12ax7 and GT 7025 tubes in them!(In the preamp section,V1 has a GT7025,V3 has a 12ax7,& V4 has a GT 7025 as well) and in the power section where V1 is suppose to be a 12DW7 there is a 12ax7A in there too! I did look on quite a few forums after this to see if this was detrimental or dangerous to the amp and couldnt find anything. However I did see mentioned that at one time a book by a guy named Aspen Pittman on svt tube conversion came out showing how to convert the SVT amps to use 12ax7 tubes instead of DW7 tubes(Ill assume this was when DW7's were very scarce) but I dont know if this amp was modifiend to do this or if someone just stuck 12ax7 tubes in place of the DW7's . IF the conversion was done on it, is it safe to switch it back to 12DW7's again or must I have it checked out (yet again?!) before doing so? Also, I do remember reading somewhere online (and sadly I cant find it now after looking for almost a hour:confused: ) that either the 12DW7 tubes or (more likely) the 12BH7 tubes must be re-biased too, just like the output tubes on this amp. Does anyone know for a fact that it is just the BH7 tubes and output 6550s, OR do those wierd 12DW7 tubes require biasing too? If it is indeed a '70s SVT it should have 12DW7s unless it was modified for the 12AX7s which isn't likely. MTI, the company that bought Ampeg from Magnavox in 1980, started out using 12DW7s but when they became difficult to source redesigned the circuitry to use 12AX7s. If your amp says Magnavox and/or Selmer it's a '70s model. The AX7s won't hurt anything but they'll alter the tone and could also be the source of your noise. All 12xxx series tubes are twin triodes which means they have two separate sections. For a 12AX7 the gain of each section is 100. For a 12AU7 the gain is 20. A 12DW7 has a gain of 100 for the first section and a gain of 20 for the second so it's half a AX7 and half of a AU7. No rebiasing is required to change preamp tubes; only the output tubes need the bias checked. I recommend using NOS or good used old 12DW7s instead of recent manufacture. The last NOS 12DW7s I bought ran about $10/each. Ebay is a good source if nothing else. Link to comment Share on other sites More sharing options...
Members dogman Posted February 22, 2008 Author Members Share Posted February 22, 2008 If it is indeed a '70s SVT it should have 12DW7s unless it was modified for the 12AX7s which isn't likely. MTI, the company that bought Ampeg from Magnavox in 1980, started out using 12DW7s but when they became difficult to source redesigned the circuitry to use 12AX7s. If your amp says Magnavox and/or Selmer it's a '70s model. The AX7s won't hurt anything but they'll alter the tone and could also be the source of your noise. All 12xxx series tubes are twin triodes which means they have two separate sections. For a 12AX7 the gain of each section is 100. For a 12AU7 the gain is 20. A 12DW7 has a gain of 100 for the first section and a gain of 20 for the second so it's half a AX7 and half of a AU7. No rebiasing is required to change preamp tubes; only the output tubes need the bias checked. I recommend using NOS or good used old 12DW7s instead of recent manufacture. The last NOS 12DW7s I bought ran about $10/each. Ebay is a good source if nothing else. Thanks misterhinkydink, and yep the amp is a blackline Magnovox era SVT. What about the 12BH7 tubes though, I couldn have sworn I read somewhere that they arent regular preamp tubes but are instead driver tubes and that they, much like power tubes, must be rebaised when you change them in an SVT(and that SVTs are different in that aspect from most other amps) Don you know if this is true or not? Link to comment Share on other sites More sharing options...
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