Troubleshooting a Single Ended KT88 Tube Amplifier Issue
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- čas přidán 24. 10. 2020
- BG284 - One of our fellow viewers built the KT88 amplifier following our Single Ended series from two years ago. However, he was pulling his hair out trying to figure out why it didn't work properly. I offered to help him out. Video shows simple basic troubleshooting steps used in fixing a vacuum tube amp.
- Věda a technologie
Nice to see you back Mark! As an amateur tech hobbyist learning the ropes I love watching diagnosing videos like this. Thanks for posting!
hear, hear! Very helpful
I built a tube amp and it never did work right. Low volume. The next door electronics expert looked at it and did not find the problem. I just put it away. Came across it again 50 years later, located the schematic and in about 10 minutes found the wiring error and fixed it. Sounds magnificent. I was 12 when I built it, from a Lafayette kit, 4 tubes. So setting these aside for a cooling off period works. Maybe it didn't need to be 50 years though.
you are so right. i worked in rf 40 years. the voltage tracing is the first place to start.
I remember an ah ha moment i had years ago, that without current or even with very low current you wont get voltage drop across the resistors... great stuff.
Excellent video. It is usually the simplest things that cause the most problems.
Thanks, Mark. Great work as usual. 👍🔊😊🎶
Splendid video. You are very kind to spread such goodness and help a buddy. Fondest regards from Devon UK. 😊
Thank you - you have done more to educate me on electronics than any other source I have come across. Your videos have empowered me to work through issues that I would have previously taken to an expert in the past. It is a true gift to the diy community.
A second set of eyes, or give it a bit of time to clear your head. Prime example is another CZcamsr I watch, Gregg's Vintage Workshop, where he is working on a 1933 Philco 54. It's a long term project where he basically had to disassemble the whole thing and completely rebuild it. Well, when he was done, it wouldn't work. Checked it 3, 4, 5 times and put it away for a couple months. Pulled it back out and started going over it again and found several mistakes. Works the charm now. So yes, another set of eyes or even some time and distance do wonders for troubleshooting clarity.
Good on ya Mark. Gives us in the hobby a good name.
Thanks again for all you do.
Second set of peepers will always help when your stranded. Good demonstration.
Nice video. I always appreciate seeing another troubleshooting process.
The bell shape curve on any given day can really swing......
Nice job Sherlock..😀
"Thou shalt check voltages." -- Dave Jones
Right. Tubes have high plate voltages. Transistor amps are low voltage devices. Tubes are voltage anplifiers. Transistors are current amplifiers (unless they are MOSFETS). Tubes have a high input impedance. They make ideal phono preamps. And tubes amplify different harmonics than transistors, so they sound better. But, tube output stage needs a transformer, because speakers are low voltage, low impedance devices. So, its a mixed bag, lol
He should have trusted his instincts, he did note that the LEDs weren't lit. I've been there too, looked at a ckt 20 times and assumed I could not have wired it wrong. Putting it away for several days and coming back to it helped find my error. Great tip on the voltmeter! It doesn't lie. Thanks for the video!
Great video, many thanks. We can't see our own mistakes. Its epecially hard after investing hours concetrating on a complex multi-skill build. A fresh set of experienced eyes can quickly sort it. There is much to learn with electronics, you have to get stuck-in. Mistakes are frustrating but by sharing the fault tracing process you will learn quickly and permanently. A great approach to diagnosing circuits is demonstrated here. Gold standard teaching.
You’re a nice guy to help him out. Thanks for the video.
Good of you to help out! Interesting that a volt meter is all one needs much of the time.
Well yes, the multimeter plus knowledge and experience. Some of us have to rely a bit more on the signal generators, cap testers etc. I can't ever remember building one single electronic project that didn't work first time, probably around 30 to 40 different circuits. A few valve and transistor amps included. I had to be extra careful, checking things multiple times, then doing it all again! That's because my understanding of theory was terrible and my fault diagnostic skills were equally as bad!
A voltmeter plus a set of eyes, ears, and nose and you can troubleshoot many faults.
And a circuit diagram (map) is incredibly useful! Use with care though because manufacturers make manufacturing mods that may differ from the published diagram.
It helps to have a good oscilloscope, so you can see everything that is going on in the circuit. (Scope should be floated, of course).
you are a good dude helping people like that .i am waiting for my transformers for this build as we speak .i cant wait for the 300b build Thanks for sharing..
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That's Awesome that you did that! Good stuff your videos are very informative I learn a little more through every one I watch.
The fresh perspective works in a surprising number of jobs. It's always good to get a second opinion when struggling with a problem.
Voltage checks are the primary tool for tubes circuits, the whole thing is one big voltage divider network, balanced at some operating point.
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lots of flak in that chassis though, owner should get that stuff out less it comes loose and shorts something out.
Cheers,
Most excellent teaching! Thank you so much.
Thank you . This is how you really learn.
Really perfectly instructive video, and nice accent by the way - thank you - cheers !
I really don't have anyone around that can help me (a second pair of eyes goes a LONG way) so what I do when something fails and I cannot figure it out within 24 hours is just put it on hold and move on --- but I always come back and fix it. I started this hobby two years ago, have built/modified/repaired over 50 projects and only one is still filed under "needs fixing" ... it was my very first kit and I fried a MOSFET one night trying to power it up with the leads reversed 😂 It's that stupid cheap "Tesla coil" audio circuit but I still want to figure out how to fix it. Meanwhile I am set to sell 5 hand wired/hand painted passive ring modulator guitar pedals!
agree, I have great trust in my understanding of Kirchhoff and Ohm, so if I mess up, can't find it, etc. I take a break and come back with those two tools and take a fresh look. Many times, voltage drops around the circuit revealed everything. Trust in your knowledge and think logically. If you get frustrated, just step away and come back with a cool head..
Having worked on a production line soldering components one issue I noticed is that I was told and is correct compliant practice to rap the leads around the terminal once, it stops the leads from breaking lose, not just rely on the solder to mechanical hold it in place.
i got inspiration to build 807 amp from your video
In software development we speak to the "cardboard programmer" i.e the process of explaining the problem (to a collegue) usually results in a ureka moment while you work out yourself what you've done wrong without your collegue saying a word!
Yeah, whiteboarding the problem usually makes the problem evident to yourself before your colleagues see it. Walking away from any technical problem for a couple of days helps too and your subconscious will often present ideas or the solution. This happens to me all the time in software dev and electronics.
And sometimes you're missing info but don't know it, so colleagues can help you realize that which may solve the problem too.
We call it talking to the duck. In my experience it always comes to you next morning in the shower.
Talking to the duck, that's good. Maybe I should shower more often? 👍
@@EJP286CRSKW I find going for a ice cream break helps.
You can rule the world with a good DMM!
I support you and subscribed! I really enjoyed your video is very informative and good explanation of the details you troubleshoot the circuits. Thank you for sharing your knowledge in the CZcams world :)
second set of eyes always helps to find mistakes and problems that's why we have QC inspectors
เยี่ยมยอด...ยอดเยี่ยม ขอบคุณที่ถ่ายทอดความรู้ดีๆมีประโยชน์ให้คอคนรักเครื่องเสียงหลอดให้รับชมครับ
Very helpful!
Excellent!
Nice repair!!!!
Good man
Love your channel
Great troubleshooting and explanation. I also plan to build this amp. but I have a question: if I do different cathode bias method on the driver tube. Is it possible to do cathode bias with a resistor and an elco on the driver tube? for 12ax7 tube, can you give recommendation what is the value for the resistor and the elco?. Thank you.
Even over CZcams digital, the SE KT88 amp sounds great!
Which proves that the tube sound is just pretty distortion.
Good job!
Nice amp, I would have thought you'd have the LED's mounted through the chasis so they are visible to the user as an indication of propper operation.
Thanks for this vedio
Thanks for sharing, and Thumbs up for helping another enthusiast out with his build.
I had plenty of these cases it can be really hard to find your own mistakes and we all do them.
First I thought it was still broken after you fixed the diode, until I realized it's a matter preferences in music, lol. I'm not judging, just realizing it's great we have vast amount of great music, so we don't all have to listen to the same tracks every day..
Joke aside, I wish I could listen to it for real without YouTiube's compression and the obvious fact that I would be listening 20 other parts in the signal path.
Is this design and the sound comparable to something familiar?
Could you pick something it rank's with?
I know the KT88 mostly from QUAD Tube amps; I had the old classic model on my ESL 63 years back, and later the QII forty, and now at QII Eighty. I Would love to try out another design with the KT's, though I have no complains over the Quads. While waiting to finishing refurbishing a set of ESL 989, need to redo the panels. A fine little winter project... or maybe next winter...
Cheers!
Absolutely loving your videos Mark all the way over here in sunny England.Would love to know who the artist is that you were using in this video to test the amp.Sounds fantastic as does the amp.
Very good
That's cool, man.
But it really says check & absolutely re-check what you have truly done. One of my biggest fails building my 1st amp grew out of not being aware of the actual size of the parts i had bought. I worked off the schematic and referred to a couple of not too good photographs in the magazine article project for my layout. On account my more modern parts were so much smaller than in the 1960s version i soon made some big mistakes. Lucky i caught it & stripped it all back for a re-start. i made a hand sketch in pencil (so i could make corrections) based on the original layout from the photos on paper. It was kind of like old Heathkits showed in their instruction manuals. I then followed it for where to fit each part to its proper place verifying on the schematic as well.....
I have built this KT88, pretty straight off his videos. Since I wanted a tube pre-amp I went out on a limb and found a good schematic and modified it to fit my needs. Having nothing to work with except a schematic I really thought the build through for around six months. Finally I bought a matching Hammond chassis 10x6x2 and all my parts. After I fabricated the chassis and placed all the components I found a whole slew of mistakes and miscalculations. Enough that I had to buy a new chassis and start over. Glad I did, the build is coming along swimmingly at this point. Just all part of the game; it is one thing to copy someone else's build, but quite another to figure things out from scratch, or even to consider different sized components like you had to do.
When I build any thing I always check the res with a ohm meter that saves a lot of time, you dont have to have a expensive meter a cheap one will do.
It is about time for a new phone.
Liked it.
Well , i have a chopstick in my toolbox , thx for the tip!! haha
That dog whining had me up looking for my dog... funny!
Hi Mark. I built your SE 807 a while back and it’s a great amp. Would you consider the KT88 to be a superior amp, given same quality components? Thanks.
Nice pointers there Mark. For this design can I simply use EL34 tubes WITHOUT changing the cathode resistor or any other components? I see on your diagram there's a list of tubes as though its a one-size- fits all. Is this really possible?
What type of speakers do you use to test equipment?
I'm getting old Rule 0.1 discharge capacitors. Learnt that waking up on the other side of the shack with a melted screwdriver courtesy of a blown discharge resistor on a colour tv.
I reminded D Jones of that fact on a power supply repair video !
He never discharged the bulk capacitors or checked the voltage .
All we got on the video is him saying …...She'll be right ….....
He could have discharged them off camera but the comment implied discharging capacitors is
irrelevant .
Dave got lucky that time & the discharge resistors did their job .
J'ai oublié:
La ligne de masse est reliée à un seul point du châssis et de préférence vers l'alimentation.
Privilégier des composants de haute qualité et aussi des composants des surplus militaires souvent à un prix plus bas avec des caractéristiques bien meilleures que les composants civils.
Courage à vous.
Can you add more speaker jacks to this build?
What a mess! I had a Leak Stereo 20 made in 1959 that was a so beautifully wired and much more intricate to boot. That amp is embarrassing fro a perspective of progress.
We all start somewhere & a failure hopefully is progress along the path of success .
A mistake is just a learning experience & fault finding practice !
First rule of amp building, check your work, second rule, check your work, third rule, check your work. It's so easy to do, we've all done it...putting a 100k R in instead of a 100r, forgetting to solder joints...DA.
Where is the schematic available for this?
Mark what does this kit cost ?
The leds not lighting was an important clue.
Hi Mark. You called that 200k a "Shade" resistor. I paused to look at the schematic and that appears to function as a negative feedback path.
If that is a feedback loop I can see why switching the 38k with the 200k would reduce volume (that would be a lot of negative feedback)
Please explain the function and the name of the "shade" resistor
Thanks.
If you will go back and watch the KT88 build series, I cover it in-depth. It's called Schade feedback.
@@Blueglow I will watch again. It's been a while since the original series began in Feb of 2018 . Thanks for creating the playlist.
200uF for a kenotrone means it's death. May be an owner needed to see one more tube on a top (instead of a mosfet regulated power source), but is this case a schematic must have a good PSRR, because 20uF is an absolute maximum for a kenotrone. Some people needs to start from JLH before they proceed to a tube amplifier -)
what is a 6N1P similar to?
ECC88 - en.wikipedia.org/wiki/6N1P
it always pays to make a hook in the end of a wire that goes to a tube socket
Phase 1 troubleshooting: It is all about Correct bias voltages If incorrect within 5-10% then it wouldn't work properly.
With hindsight(!) the clue was in the builder's fault description - '........diodes not lit.'
Ah but there were two other problems though. Fixating on correcting LED orientation may cause the other problems to be missed and the thing works.. ok but not great. I agree that customer complaint is important but it's also good to put it aside and go through a soup-to-nuts diagnostics approach. I have had more than one customer tell me the problem only to find that it's something wildly different at fault.
Cheers,
@@EngineeringVignettes Agreed, but it would have been a good starting point, with the routine checks to follow.
also looks like he used lead free solder. i knew things were changing when i retired in 09 but i just could not use it.Every joint looked cold when i used it. yuck
Total rubbish. Thanks, elf'n'safety.
Rule 1 - thou shalt check voltages. As true now as it was donkeys; years ago.
Le câblage n’est pas bien propre.
Il faut prévoir une bonne ligne de masse de l’entrée à la sortie afin d’éviter des boucles de masse provoquant du hum et un signal de qualité moyenne.
Faire des connexion repliées sur les sockets des tubes et sur les barettes relais ( l’ampli doit pouvoir fonctionner sans soudure).
Penser à rajouter une résistance bleeder entre le b+ et la masse.
Privilégier des connexions courtes et du câble de bonne qualité.
Penser à poser un potentiomètre anti hum entre b+ et filaments.
Et surtout, de la patience...
DAJTE RAZMENITE TU SHEMU U PDF.HVALA
a typical beginners disease....as well as getting polarity wrong on electrolytics.....once you find out, you never do that again. That's the learning proces. The main symptoms for you is : you get nightmares.The remedy : check your voltages. Happened on my first two amps.
OK.✌️✌️✌️✌️😍😍😍😚👄👄👄
"COMPLETELY OFF TOPIC ALERT!" - Sorry to interrupt your regularly scheduled programming, but I'm kind of new to this channel and am looking for a reputable online seller of tubes. NOS is not required, but wanted to find out where all the groovy kids buy their tubes. Thanks!
"We now return you to your regularly scheduled programming....." 💩"Howdy Hoooo!"
Shady Jake the Tube Snake. He's your man. Long wait for shipping from China though...
800 bucks for a single ended amplifier lol