Greetings.
I just fired up my first tube amp kit build(Mod 102) from amplifiedparts.com. It is a 5w. single ended, cathode biased amp, that has one 12ax7 preamp tube, and one EL84 power tube. It functions as it should, except for one problem. It hums loudly(60 Hz., I believe), and if you try to touch the El84 tube, even before you can touch it(about 2 inches from the tube) it begins a high pitched squeal, that gets louder, the closer you get, until when you touch the tube, it squeals loudest, and I mean LOUD. I've heard hum before in a tube amp, but never have I heard this squeal. This does not happen if you approach the 12ax7 tube.
I hope to get a reply from somebody who has advice concerning this problem. I had a problem with the kit, that I couldn't figure out, and did not have the time to troubleshoot it properly, so I sent it back to amplified parts(paying only shipping both ways) to let their tech make it right. They let me know, that I had an erroneous jumper to ground and fixed it. However, they had removed the power tubes cathode resistor and the electrolytic cap in parallel with it, and left it in the bottom of the box. Of course, the only thing the amp would do, was, when turned on, the pilot lamp lit up.....no sound. So, I replaced the resistor and cap, which checked out fine, and now the kit amplifies O.K. It's just this constant hum, and the squeal when you approach/touch the EL84. The hum does not change when you touch the guitars strings.
PLEASE HELP ! I waited on this thing for nearly a month, and paid an extra $40.00 in shipping to let them "FIX IT", so right now I've spent $255.00 on the $215.00 kit, and I still can't use it !
I just fired up my first tube amp kit build(Mod 102) from amplifiedparts.com. It is a 5w. single ended, cathode biased amp, that has one 12ax7 preamp tube, and one EL84 power tube. It functions as it should, except for one problem. It hums loudly(60 Hz., I believe), and if you try to touch the El84 tube, even before you can touch it(about 2 inches from the tube) it begins a high pitched squeal, that gets louder, the closer you get, until when you touch the tube, it squeals loudest, and I mean LOUD. I've heard hum before in a tube amp, but never have I heard this squeal. This does not happen if you approach the 12ax7 tube.
I hope to get a reply from somebody who has advice concerning this problem. I had a problem with the kit, that I couldn't figure out, and did not have the time to troubleshoot it properly, so I sent it back to amplified parts(paying only shipping both ways) to let their tech make it right. They let me know, that I had an erroneous jumper to ground and fixed it. However, they had removed the power tubes cathode resistor and the electrolytic cap in parallel with it, and left it in the bottom of the box. Of course, the only thing the amp would do, was, when turned on, the pilot lamp lit up.....no sound. So, I replaced the resistor and cap, which checked out fine, and now the kit amplifies O.K. It's just this constant hum, and the squeal when you approach/touch the EL84. The hum does not change when you touch the guitars strings.
PLEASE HELP ! I waited on this thing for nearly a month, and paid an extra $40.00 in shipping to let them "FIX IT", so right now I've spent $255.00 on the $215.00 kit, and I still can't use it !
A schematic diagram would help us help you.
quite possibly you have a soldering error. A cold joint can leave a grid open and subject to oscillation when any sort of antenna (like a finger) is brought near it.
Hum should be checked first by shorting the inputs to the amp with clip lead or soldered wire. Then check the 60 hz on the power supply cap, with a dvm. This should be fairly low. If it is, check the DC on the grid to the output tube. If it is per design, 1 to 20 v, then put a .47 uf capacitor to ground there and see if the hum goes away. If it doesn't, the hum is in the output stage. If the hum does go away, something in the input stage is humming. Note wires to high gain stages, like 12ax7 grids, should not run parallel to wires carrying 120 vac current.
Dynaco told the builder where to run the wires with diagrams, so none of my tube amps (the others professionally built by Hammond Organ) have had this problem. The dynacos had a steel case around the power transformers, and the high gain wires in a separate steel box from the the AC wires, power switch, and AC pilot light. This was done with a steel bulkhead inside the steel chassis of the PAS2. It is a practice I follow with my solid state designs.
quite possibly you have a soldering error. A cold joint can leave a grid open and subject to oscillation when any sort of antenna (like a finger) is brought near it.
Hum should be checked first by shorting the inputs to the amp with clip lead or soldered wire. Then check the 60 hz on the power supply cap, with a dvm. This should be fairly low. If it is, check the DC on the grid to the output tube. If it is per design, 1 to 20 v, then put a .47 uf capacitor to ground there and see if the hum goes away. If it doesn't, the hum is in the output stage. If the hum does go away, something in the input stage is humming. Note wires to high gain stages, like 12ax7 grids, should not run parallel to wires carrying 120 vac current.
Dynaco told the builder where to run the wires with diagrams, so none of my tube amps (the others professionally built by Hammond Organ) have had this problem. The dynacos had a steel case around the power transformers, and the high gain wires in a separate steel box from the the AC wires, power switch, and AC pilot light. This was done with a steel bulkhead inside the steel chassis of the PAS2. It is a practice I follow with my solid state designs.
Well here is his schematic:
http://www.amplifiedparts.com/sites/default/files/assoc_files/mod_102_schematic.pdf
And the layouts are contained in this:
http://www.amplifiedparts.com/sites/default/files/assoc_files/mod102_assembly_drawings_0.pdf
I'd have to agree, you missed a connection or made a mistake. It seems like maybe an unterminated grid on the power tube. Maybe?
http://www.amplifiedparts.com/sites/default/files/assoc_files/mod_102_schematic.pdf
And the layouts are contained in this:
http://www.amplifiedparts.com/sites/default/files/assoc_files/mod102_assembly_drawings_0.pdf
I'd have to agree, you missed a connection or made a mistake. It seems like maybe an unterminated grid on the power tube. Maybe?
Greetings Enzo and Indianajoe.
Thanks for replying. I have to admit to you that this problem was an elementary issue completely missed by me. The problem is still mysterious, as it doesn" t effect my Blackstar. However, I found a broken string earth ground on my guitar, I fixed it and the noise level really went down. it is not perfect yet, but playable, and with your advice, I will try to improve it. I really appreciate your advice, especially on such a subject were there can be many causes. I wish that I had your experience/intuition for such "mysteries? I will check lead dress, soldering quality, and the other things you have suggested. Greet to hear from you both.Best Regards tonequester.
Thanks for replying. I have to admit to you that this problem was an elementary issue completely missed by me. The problem is still mysterious, as it doesn" t effect my Blackstar. However, I found a broken string earth ground on my guitar, I fixed it and the noise level really went down. it is not perfect yet, but playable, and with your advice, I will try to improve it. I really appreciate your advice, especially on such a subject were there can be many causes. I wish that I had your experience/intuition for such "mysteries? I will check lead dress, soldering quality, and the other things you have suggested. Greet to hear from you both.Best Regards tonequester.
Hi tonequester. It might be a long shot, but check the el84 socket for flux mess from soldering. Some fluxes can quickly become conductive and it could be giving you a feedback loop.
Hum and Squeal.
Thanks doozerdave.
I appreciate the advice on the flux residue in the tube socket terminals. I'll definitely make sure they are clean. However, I found out something that got rid of MOST of the hum/buzz. Talk about "stupid simple". I had blocked my tremelo with a chunk of hardwood. I'm just not into tremelo at all. So, I followed Eric Claptons lead. I was checking out one of Gerald Weber's books on tube amps, and one statement "hit me where it hurts". "If you unplug the guitar, and the hum goes away, the guitar is humming, not the amp" ! So, I checked this out, and sure enough, the amp stopped humming when I unplugged. Then, it was "what the Hell is wrong with my Strat". I somehow got luck right off. I realized that in getting rid of the trem's springs, I had "cut" the string earth ground. I put two springs back on, checked out the re-newed continuity that I now had, plugged into the amp and.....very little hum/buzz.
Now I am left with one problem. When you hit 8 on the volume control, the amp starts to motorboat, and that increases as you max out the volume. I contacted amplifierparts.com(who makes the kit) and their tech had some sage words for me...."turn the volume down" !!!! Now I'm reading about motorboating ! So. if you have had any experience on this, give me a hollar IF you have time !
Once again, thanks for the reply. I really appreciate the help. The kits been a curse instead of a blessing, so far ! tonequester....clueless most of the time.
Thanks doozerdave.
I appreciate the advice on the flux residue in the tube socket terminals. I'll definitely make sure they are clean. However, I found out something that got rid of MOST of the hum/buzz. Talk about "stupid simple". I had blocked my tremelo with a chunk of hardwood. I'm just not into tremelo at all. So, I followed Eric Claptons lead. I was checking out one of Gerald Weber's books on tube amps, and one statement "hit me where it hurts". "If you unplug the guitar, and the hum goes away, the guitar is humming, not the amp" ! So, I checked this out, and sure enough, the amp stopped humming when I unplugged. Then, it was "what the Hell is wrong with my Strat". I somehow got luck right off. I realized that in getting rid of the trem's springs, I had "cut" the string earth ground. I put two springs back on, checked out the re-newed continuity that I now had, plugged into the amp and.....very little hum/buzz.
Now I am left with one problem. When you hit 8 on the volume control, the amp starts to motorboat, and that increases as you max out the volume. I contacted amplifierparts.com(who makes the kit) and their tech had some sage words for me...."turn the volume down" !!!! Now I'm reading about motorboating ! So. if you have had any experience on this, give me a hollar IF you have time !
Once again, thanks for the reply. I really appreciate the help. The kits been a curse instead of a blessing, so far ! tonequester....clueless most of the time.
" I wish that I had your experience/intuition for such "mysteries?"
Hey Tonequester! You are getting your wish as you speak..... Building your own amp is the ONLY way to gain experience and intuition. Believe me I know! I am about to start wiring up only my second amp (see pics), which I already know how it will sound, having built it on my breadboard, but am almost certain it will not perform as expected when I finish the build, even after double and triple checking everything I can think of.... I have had it working great one minute, then after changing something have it start acting screwy, and have to go thru EVERY solder joint and wire connection, only to find a ground I didn't reconnect or a bad solder joint! This is how you learn. And keep a log of what you find, to remind you of what to check next time it happens, because it will (LOL). Good luck, and keep posting, so I can continue to learn from all the knowledge you and all the other great guys on this forum have to share! Jeff
Hey Tonequester! You are getting your wish as you speak..... Building your own amp is the ONLY way to gain experience and intuition. Believe me I know! I am about to start wiring up only my second amp (see pics), which I already know how it will sound, having built it on my breadboard, but am almost certain it will not perform as expected when I finish the build, even after double and triple checking everything I can think of.... I have had it working great one minute, then after changing something have it start acting screwy, and have to go thru EVERY solder joint and wire connection, only to find a ground I didn't reconnect or a bad solder joint! This is how you learn. And keep a log of what you find, to remind you of what to check next time it happens, because it will (LOL). Good luck, and keep posting, so I can continue to learn from all the knowledge you and all the other great guys on this forum have to share! Jeff
Attachments
Comments on your amp kit: I notice the 6.3VAC is not grounded to the chassis, like Fender does (and myself). Looks like it will work. Have read about elevating one side slightly above ground (to reduce hum).....know there is something to learn in there somewhere.... And no eyelet/turret board, just old school terminal strips! Works for a small design, I guess, and keeps it simpler.
Keep after IT !!!
Greetings latubegeek
Hey bro', thanks for replying to my post, and glad to "meet" you.
I've been "tubin" for about 33 years, and the repairing/modding of tube amps, along with my work on guitars, has been one of the few things, that I have ever stuck with. What little I know, I learned just as you are doing. t's kind of strange that I am just now getting around to building an amp kit. It's a shame that the Mod 102 is inherently flawed, by having too small of a chassis to allow for a clumsy old fool like me to really do a good job with the lead dress. Not only clumsiness, but not so good eyes anymore do hinder. If the kit had a chassis 50% bigger, it would be a much easier build. I finally got the thing up and running. However, it motorboats at full volume. I contacted the tech at amplified parts, and he had the answer. "Turn down the volume" !!! If that weren't bad enough, he told me that he suspected that it was do to the small chassis ! That was the first complaint that I had related to them. There drawings(which I had checked out online before buying) give one the impression that there is much more "room under the hood". I wanted an amp that I could crank up full blast, and get power tube saturation.
Live and learn ! Now I am going to build from scratch. I've got a nice roomy chassis just waiting. I thought about doing that first off, but thought a kit would be good experience. It would have been so, if I had not chosen the Mod 102. I plan on building the same type of amp(Class A, single ended, cathode biased) because I like that sound. However, I am thinking of paralleling the EL84 to get just a little more power out of it. There were several things about the Mod 102 that I would have done differently, and now I can address those issues. Anyway, I hope that you continue to have good results form YOUR builds. Your always welcome to reply to any of my posts. I'm of a mind that "old dogs" can learn new tricks....even form "young dogs". It sounds like you are well on your way to understanding some of the "mystery" that surrounds vacuum tube technology. If you PLAY them as well, you already know how superior and versatile the tube amp is. Don't make the mistake in buying a "hybrid" like I did one time. When I bought it, the word was "studio quality practice amp", by the time they had replaced 3 of them under the years warranty(and I was getting peaved) it suddenly became an "entry level amp" ! Hundreds down the drain. I fixed the last one myself, voiding the warranty, but getting a functional amp. I found out on a forum, by a tech that is authorized to work on them, that it is built in China for about $25.00. I'm usually not a "name dropper" but I'll drop a turd here....Blackstar.
Keep on keepin" on my friend, and Best of Regards.....tonequester.
Greetings latubegeek
Hey bro', thanks for replying to my post, and glad to "meet" you.
I've been "tubin" for about 33 years, and the repairing/modding of tube amps, along with my work on guitars, has been one of the few things, that I have ever stuck with. What little I know, I learned just as you are doing. t's kind of strange that I am just now getting around to building an amp kit. It's a shame that the Mod 102 is inherently flawed, by having too small of a chassis to allow for a clumsy old fool like me to really do a good job with the lead dress. Not only clumsiness, but not so good eyes anymore do hinder. If the kit had a chassis 50% bigger, it would be a much easier build. I finally got the thing up and running. However, it motorboats at full volume. I contacted the tech at amplified parts, and he had the answer. "Turn down the volume" !!! If that weren't bad enough, he told me that he suspected that it was do to the small chassis ! That was the first complaint that I had related to them. There drawings(which I had checked out online before buying) give one the impression that there is much more "room under the hood". I wanted an amp that I could crank up full blast, and get power tube saturation.
Live and learn ! Now I am going to build from scratch. I've got a nice roomy chassis just waiting. I thought about doing that first off, but thought a kit would be good experience. It would have been so, if I had not chosen the Mod 102. I plan on building the same type of amp(Class A, single ended, cathode biased) because I like that sound. However, I am thinking of paralleling the EL84 to get just a little more power out of it. There were several things about the Mod 102 that I would have done differently, and now I can address those issues. Anyway, I hope that you continue to have good results form YOUR builds. Your always welcome to reply to any of my posts. I'm of a mind that "old dogs" can learn new tricks....even form "young dogs". It sounds like you are well on your way to understanding some of the "mystery" that surrounds vacuum tube technology. If you PLAY them as well, you already know how superior and versatile the tube amp is. Don't make the mistake in buying a "hybrid" like I did one time. When I bought it, the word was "studio quality practice amp", by the time they had replaced 3 of them under the years warranty(and I was getting peaved) it suddenly became an "entry level amp" ! Hundreds down the drain. I fixed the last one myself, voiding the warranty, but getting a functional amp. I found out on a forum, by a tech that is authorized to work on them, that it is built in China for about $25.00. I'm usually not a "name dropper" but I'll drop a turd here....Blackstar.
Keep on keepin" on my friend, and Best of Regards.....tonequester.
Are you still with a motorboating amp ? If I was you I would try to move the screen connection of EL84 to B1 , it seems to me a strange thing to use the same supply of preamp to supply the screen of a power tube, better to use the same supply for plate and screen using only the 1K resistor.
Also i would add a grid stopper on the first stage, putting a 47 to 65K in series with the grid of the first tube.
What is made me thinking is they're using the chassis as ground via terminal strips instead of using a star ground design...
Also i would add a grid stopper on the first stage, putting a 47 to 65K in series with the grid of the first tube.
What is made me thinking is they're using the chassis as ground via terminal strips instead of using a star ground design...
Greetings Tesla88.
Thanks for your reply. You are absolutely correct about the grounding scheme of the kit. All grounds are made with terminal strips. When I got the kit and realized this, I had a bad feeling about it, but thought "OH, well, they must know what they're doing. They DON"T ! I wish I had never bought the hunk of junk. Beginners kit my eye ! Their customer "service" sucks as well. I spent another $40.00 to send it in for THEM to fix, as THEY offered. It was after I got it back, with loose parts in the bottom of the box(which I then re-installed) that the motorboating problem became clear. When I contacted them about the motorboating, their "techs" advice was......"turn the volume down". Then they told me that it was due to the chassis being so small. I had complained about THAT right after I received it in the mail. Half of the soldering had to be done basically "blind".
I don't have time for screwing around with such rip-offs. I learned a lesson. Don't rely on the diagrams offered by kit makers. pay attention to the exact dimensions given. Their pictures were totally misleading. It looked as if one had plenty of room to spare in the chassis. In reality, it was impossible to do a good job on lead dress. The $245.00 mistake, is now residing where it belongs......in my spare parts/junk pile. Anybody who buys the Mod 102 kit from amplifiedparts.com is in for more than they bargained for. I could have lived and dealt with every problem, except one. THAT problem is that they pretend to have customer service. IT"S A LIE !!! They left me in worse shape than I was when I sent it in to have the problems resolved. I bought this thing, not only to build, but to play. I need a small amp. I needed it in October of last year. it's soon to be February. And I still don't have a small tube amp. I'm going to buy a VTS Special Ultra. It is hand wired, and they use eyelet board. It's advertised as mod friendly, and you can even use their $15.00 adapter to change the 6V6's to EL84's. The next amp I build will be from scratch, when I have the time. The VTS is $399.99, but that's only $155.00 more than I have spent on absolute junk, not to mention my many wasted hours.
Thanks for your reply, I have the feeling that your suggestions could have been exactly what "the doctor ordered", but "the doctor" has no more time to **** away on a scam, and rip-off. I do appreciate your attempt to help me out, and I won't forget it Tesla88.
I have proved one thing for sure : "You're never too old to get ripped-off."
tonequester.
Thanks for your reply. You are absolutely correct about the grounding scheme of the kit. All grounds are made with terminal strips. When I got the kit and realized this, I had a bad feeling about it, but thought "OH, well, they must know what they're doing. They DON"T ! I wish I had never bought the hunk of junk. Beginners kit my eye ! Their customer "service" sucks as well. I spent another $40.00 to send it in for THEM to fix, as THEY offered. It was after I got it back, with loose parts in the bottom of the box(which I then re-installed) that the motorboating problem became clear. When I contacted them about the motorboating, their "techs" advice was......"turn the volume down". Then they told me that it was due to the chassis being so small. I had complained about THAT right after I received it in the mail. Half of the soldering had to be done basically "blind".
I don't have time for screwing around with such rip-offs. I learned a lesson. Don't rely on the diagrams offered by kit makers. pay attention to the exact dimensions given. Their pictures were totally misleading. It looked as if one had plenty of room to spare in the chassis. In reality, it was impossible to do a good job on lead dress. The $245.00 mistake, is now residing where it belongs......in my spare parts/junk pile. Anybody who buys the Mod 102 kit from amplifiedparts.com is in for more than they bargained for. I could have lived and dealt with every problem, except one. THAT problem is that they pretend to have customer service. IT"S A LIE !!! They left me in worse shape than I was when I sent it in to have the problems resolved. I bought this thing, not only to build, but to play. I need a small amp. I needed it in October of last year. it's soon to be February. And I still don't have a small tube amp. I'm going to buy a VTS Special Ultra. It is hand wired, and they use eyelet board. It's advertised as mod friendly, and you can even use their $15.00 adapter to change the 6V6's to EL84's. The next amp I build will be from scratch, when I have the time. The VTS is $399.99, but that's only $155.00 more than I have spent on absolute junk, not to mention my many wasted hours.
Thanks for your reply, I have the feeling that your suggestions could have been exactly what "the doctor ordered", but "the doctor" has no more time to **** away on a scam, and rip-off. I do appreciate your attempt to help me out, and I won't forget it Tesla88.
I have proved one thing for sure : "You're never too old to get ripped-off."
tonequester.
It sounds as if you've got blocking distortion. Do you have grid stoppers on both gain stages?
I looked at the schematic briefly but only remember seeing one gain/volume control. Grid stoppers can be just about any size (ohm) 100k is a good starting point.
Does the EL84 have a grid stopper? They really should , a 220k would be good for it.
I looked at the schematic briefly but only remember seeing one gain/volume control. Grid stoppers can be just about any size (ohm) 100k is a good starting point.
Does the EL84 have a grid stopper? They really should , a 220k would be good for it.
It sounds like you have the makings of what I think of as a High Octane ... check out this you tube video of one. It's basically 2 x 12ax7 preamp with a single ended EL84 power section.... the MOD 102 is basically what I think of as the P1 which when adding the second 12ax7 is the high octane.
Enjoy
AX84.com Hi-Octane Amp Clip - YouTube
Enjoy
AX84.com Hi-Octane Amp Clip - YouTube
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