derrickdj1 Posted August 13, 2016 Share Posted August 13, 2016 Over the last week, the two channel amp has been sounding short on clarity and fading in and out. I checked all the wiring and couldn't figure out what was going on. This amp has been running near 4 years. So, I changed all 4 tubes and that fixed the problem. The Yaqin VK 2100 is a tube hybird. The preamp uses 4 tubes, 6N1. I replaced them with 4 NOS tubes(Russian). I brought 16 of them when I purchased the amp These are for voltage and drivers. I don't know what is meant by for voltage and drivers. The rear of the amp is : Output Transistors: 2SA943 x 2 and 2SC5200 x 2 (Toshiba Japan) . As far as I know, the tubes just pop in and you are ready to go. No bias is needed? How long should preamp tubes last? Is there a way to check them? Do hybird amps soft or hard clip? I am a noob when it comes to tube amp. I should mention that the amp sounds fantastic and has been problem free every since I purchased it around 4 years ago. Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 13, 2016 Author Share Posted August 13, 2016 29 minutes ago, derrickdj1 said: Over the last week, the two channel amp has been sounding short on clarity and fading in and out. I checked all the wiring and couldn't figure out what was going on. This amp has been running near 4 years. So, I changed all 4 tubes and that fixed the problem I think. I need to spend some listening time with the amp The Yaquin VK 2100 is a tube hybird. The preamp uses 4 tubes, 6N1. I replaced them with 4 NOS tubes(Russian). I brought 16 of them when I purchased the amp These are for voltage and drivers. I don't know what is meant by for voltage and drivers. The rear of the amp is : Output Transistors: 2SA943 x 2 and 2SC5200 x 2 (Toshiba Japan) . As far as I know, the tubes just pop in and you are ready to go. No bias is needed? How long should preamp tubes last? Is there a way to check them? Do hybird amps soft or hard clip? I am a noob when it comes to tube amp. I should mention that the amp has sounded fantastic and has been problem free every since I purchased it around 4 years ago. Quote Link to comment Share on other sites More sharing options...
Lemon string Posted August 13, 2016 Share Posted August 13, 2016 Hey Derrick Im not an expert but I would guess the pre tubes to be good for a long time, like up to ten years (10,000 hrs). I might be way off on that. Glad you found the remedy none the less. Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 13, 2016 Author Share Posted August 13, 2016 Thanks Seth, This set ran 4 years. I brought the amp used so I don't know how many hours was on the tubes. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted August 13, 2016 Share Posted August 13, 2016 Derrick, the 4 6N1s simply act as voltage amplifiers to provide the output transistors with what they need to furnish the desired power. The 4 tubes do not need to be biased manually and, as you stated, you can just pop them in and forget about it. As to longevity, it all depends on how they are used in the circuit. One of the biggest issues is filament voltage- if it runs more than 10% higher than spec, it could result in shortened tube life. I can't speak for modern tubes as I don't use them- NOS voltage amplifier tubes, if run appropriately, can last "forever" meaning 50-100k hours. The transistor output stage should have adjustable bias, and that can be important to prevent the transistors from running excessively hot. In addition, the dc offset of the output stage is normally adjustable. This can be important since excessive exposure to high dc levels can potentially be harmful to speaker drivers. The manual may tell you how to check these 2 operating parameters and adjust them to be within spec if found to be off. Lastly, clipping in hybrid amps is usually the same as it would be in an all solid state unit as it will be dictated by the performance of the output transistors. Maynard Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 13, 2016 Author Share Posted August 13, 2016 Thanks for the insightful reply. Unfortunately I don't have a manual and can't find one on line. I guess if I suspect any problems, I can have someone look at it. The amp does not seem to run hot. I have had some ss amp run much hotter than this runs. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted August 14, 2016 Share Posted August 14, 2016 16 hours ago, derrickdj1 said: Thanks for the insightful reply. Unfortunately I don't have a manual and can't find one on line. I guess if I suspect any problems, I can have someone look at it. The amp does not seem to run hot. I have had some ss amp run much hotter than this runs. If the amplifier sounds better after replacing the driver tubes and still runs cool, I wouldn't worry much. If you are concerned about DC offset, (excessive DC voltage at the outputs) and have a multi-meter that measure in millivolts, you can measure the DC offset at the outputs. (speaker jacks) If there is more than a volt DC at one of the output jacks, then that's not a good thing. If in the millivolt range, then that's okay. One can get sort of an idea on the difference in bias between each side (R,L) of the amplifier from this approach. The difference in millivolts between right an left side of the amplifier should be minimal. They won't measure exactly the same, but there will be a difference. If there is a big difference with the millivolt measurement for each side of the amp, then there could be a problem. Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 14, 2016 Author Share Posted August 14, 2016 Thanks Mike. Things seem to be Ok. The multimeter sound easy enough to do. I may pick one up tomorrow at Harbor Freight. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted August 15, 2016 Share Posted August 15, 2016 11 hours ago, derrickdj1 said: Thanks Mike. Things seem to be Ok. The multimeter sound easy enough to do. I may pick one up tomorrow at Harbor Freight. I need to do the same (DC offset check) with a Marantz 2220B receiver from a employee/friend. The guy complained the tuner in the receiver didn't work very well...one reason being he had the antenna hooked up incorrect, but the main reason is the unit must have sat for a rather long time. The environment in which it was stored had low humidity fortunately, but the dust factor was high. I pulled the cover to be greeted by a good quarter inch of crusty dust bunnies...no wonder the tuner didn't work. it also had a piece of choker chain necklace dangling off a transistor's leads, but it still worked and wasn't shorted. OCD kicked in and I managed to brush, blow, and vacuum everything the best I could, along with disassembling and cleaning the front panel. Too bad the top of the unit wasn't covered when it was stored... Cleaned out the gears in the tuner, pulleys for the string, and some slight adjustments. It can get plenty of stations now. All it needs now are the rear panel lights... Quote Link to comment Share on other sites More sharing options...
dirtmudd Posted August 15, 2016 Share Posted August 15, 2016 On 8/14/2016 at 11:18 AM, derrickdj1 said: Thanks Mike. Things seem to be Ok. The multimeter sound easy enough to do. I may pick one up tomorrow at Harbor Freight. Try this.. http://www.srs-webstore.com/pages/biastool.html 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 17, 2016 Author Share Posted August 17, 2016 Well, I was playing the amp last night and seen a spark go off in the amp thru the front glass. This one is going to tube heaven. Repair cost would be more than I paid for the amp. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted August 17, 2016 Share Posted August 17, 2016 27 minutes ago, derrickdj1 said: Well, I was playing the amp last night and seen a spark go off in the amp thru the front glass. This one is going to tube heaven. Repair cost would be more than I paid for the amp. You need to pull it apart and see if you notice anything obvious. There's knowledgeable people here that can probably help you fix it and provide safety precautions as well. I never throw anything apart without having a look inside. 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted August 17, 2016 Share Posted August 17, 2016 Carl is absolutely correct! Just because you saw something spark doesn't mean that the amp is ready for the trash bin. It's possible that one of the new tubes you installed arced internally and replacing it will restore normal operation. If you remove the cover, and don't see any burned components on the board, it's fine to do this. You could try replacing the 4 tubes one at a time with an old one (since you know they are good) to see what happens. If a tube is going to fail it often occurs within the first few hours of use. Please post with the results if you give this a try! Maynard Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted August 18, 2016 Author Share Posted August 18, 2016 I did open the amp. Nothing is burned and no smell. close inspection shows two blown fuse on the far right. I have be using an amp selector to switch back and forth between the tub amp and SS. I am wondering if the the amp selector malfunction and current from the SS feed back into the thube amp. I guess I should try some replacement fuses and see how the unit functions. Everything in the amp looks good and shown no signs of wear. I wonder is a problem with a fuse could have lead to the fading and distance sound that was intermittently happening? Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted August 18, 2016 Share Posted August 18, 2016 Unplug everything from the amp selector and check it the selector with an ohm meter to be sure that you don't have continuity in places you shouldn't based on switch position. Quote Link to comment Share on other sites More sharing options...
USNRET Posted August 18, 2016 Share Posted August 18, 2016 Just a mechanic here but If I were left alone to my on to troubleshoot, I would disconnect everything from the amp, power up for a short time to to see if the fuse(s) blow, power down, cool tubes, connect just the speakers and power back up, allow to warm up (if no issue), power down, cool down, connect source / the pre-amp, rinse and repeat with a source to check for sound; again stopping if anywhere in the process causes an issue. Me NO electronix repair guy. Quote Link to comment Share on other sites More sharing options...
dtr20 Posted August 18, 2016 Share Posted August 18, 2016 1 hour ago, USNRET said: Just a mechanic here but If I were left alone to my on to troubleshoot, I would disconnect everything from the amp, power up for a short time to to see if the fuse(s) blow, power down, cool tubes, connect just the speakers and power back up, allow to warm up (if no issue), power down, cool down, connect source / the pre-amp, rinse and repeat with a source to check for sound; again stopping if anywhere in the process causes an issue. Me NO electronix repair guy. I don't know much about tube amps, but I was told never power them on without being hooked up to speakers Quote Link to comment Share on other sites More sharing options...
USNRET Posted August 18, 2016 Share Posted August 18, 2016 20 minutes ago, dtr20 said: I don't know much about tube amps, but I esa told never power them on without being hooked up to speakers I was leery of that myself not knowing squat but during a time of troubleshooting a tube amp of mine a well known member / builder had me do just that.....for a short time. I did NOT sleep in a Haliday IN last night so... Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted August 18, 2016 Share Posted August 18, 2016 Derrick, the two blown fuses should be in the p/s rail for the output transistors. The flash you saw was the elements of the fuses burning up. It's quite reasonable to try replacing them (be sure to use the exact value specified, and they must be slow blow types as are the originals!!!). Be sure to first unplug the amp from the wall. With the sources and speakers disconnected you can try turning it on. If, by chance, you have a variac you can power it up slowly while monitoring the current drawn. You will know quickly enough if there's an issue based on excessive draw (for example, if you see 2 or 3 amps being drawn with a line voltage of only 40 or 50 then forget it). If all seems well, connect your speakers (do not use the switch box- connect them directly) and listen for any unusual noise with the volume control down all the way. You can then advance the volume control to listen for excessive hiss/noise which wasn't there before. And, if that seems ok, turn down the volume control all the way (or shut the amp off), connect one source directly to the amp, and give it a listen. As far as turning on a tube amp with no speakers connected, that is perfectly safe as long as no signal is applied to the input (in some amps, even doing that won't be an issue but it isn't good practice). Maynard Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted August 18, 2016 Share Posted August 18, 2016 You could always throw together one of these. If there's a dead short in the amp, the light will shine. https://community.klipsch.com/uploads/monthly_04_2016/post-13087-0-88480000-1460242326_thumb.jpg Link to thread below. If you're interested, I think I can find the instructional video on how to build one. Quote Link to comment Share on other sites More sharing options...
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