I learn so much by watching you systematically diagnose these issues. Im learning it's all about a process of elimination. Please keep these videos coming. Thank you.
Excellent thanks for the feedback. It's interesting to how someone with 5 decades of fault finding experience can still (and often) scratch their head and say "What the $%^& is going on???"!
You said you hoped this video was interesting, and you hoped that it wasn’t boring. Mr. Smith, all of your videos are educational as far as I am concerned. Tracking down a hum source or multiple sources is educational and I learn more times than not. I am not formally educated in elections, I learned what I know from online courses and from people like yourself. It is nice to have the benefit of someone like yourself and your experience to fill in the gaps of the knowledge that I have. If I was younger I would go back to school for electronics. I’m not what you would call old but I’m not young anymore either. I am retired in my late fifties, my son has a decent sized and reputable recording studio in Pittsburgh, PA. He is a professional touring musician as well. I do a lot of work for him as well as other musicians. I appreciate what you do, and please never think that it’s boring or too long. I use many diagnostic approaches from you. Thank you sir!! Lee
@@leecaruso5695 It's a complete pain tbh. If someone even mentions a website in a comment it gets pulled. Maybe it's something to do with preventing unwanted spam.
I don’t know but I do know how things have changed in a brief period of time. And I don’t think it’s going to get any better. Unfortunately. This cleaner is very good, if you try it I believe you will use it in stead of the other one with the god awful new design for delivery. Lol. I love what you do and I watch all the time. Thanks for spending the time to do what you do.
An easy way to determine the value of resistors in parallel using a calculator. Clear the memory, enter the value of R1, take its reciprocal, and add it to memory. Enter the value of R2, take its reciprocal, and add it to memory. Recall the memory, take its reciprocal, which is your answer. This works for any number of resistors in parallel. For two resistors in parallel, the formula simplifies to Rtot = R1 x R2 / (R1 + R2), known as the ‘product over sum rule’. Incidentally, both the above methods result in 45.9 Ohms.
I always enjoy your videos but this one was especially informative for me with regards to grounding (earthing) schemes. I have built a couple of early Marshall 100 watt clones over the past few years; and while they do not exhibit a great deal of hum I think they can be better. This video has given me some pointers in the right direction I believe.
Excellent job on the amp. I just repaired my Marshall DSL for a humming / crackling noise. Long story short, the new power tubes I put in were defective and it took a week of headscratching to sort it out. The problem was the tubes as I originally thought. Sometimes that's how it goes🤷♂️
It's fascinating, extraordinary, now look, no hum. I'm poking a little humor here, but I've learned when building amplifiers, it has been quite a lot better using aluminum chassis. Crazy stuff. Great video. Thanks, Cheers 😀
This hum issue can be so frustrating! I remember an instructor in an electrical class I was in years ago speak about how just the most minute length of wire +/- can cause EM crosstalk, Rf transmission , receiving,etc.. I have also in my own experience,been able to cut a few inches off of a guitar cable to stop it receiving radio signal. I have never seen something like you are dealing with here though. Wow! the same ground lug producing a different potential from one side to the other. That’s a head scratcher for sure. Great job getting that to a reasonable level.
Hard to tell, but if it’s an early Aluminium chassis, they were dodgy! Glad you sorted it! Cheers Stuart! Those had KT66 valves in them. That’s probably from 1965, in 1966 they went to EL34’s..
I can tell you from experience that a poor connection between the pots and the chassis will cause an earth hum. Simply undoing the pots and doing them up again can shut a hummy sixties Marshall up. Sounds like nonsense, but it's a fact - and I do an awful lot of work on these old things. Beautiful amplifier though Stuart. I also always change the Bias caps because as you've said, if the voltage goes down, the Bias goes up and all hell breaks loose lol Original valves would've been 6L6 or EL34. You can tell what valves it should have in it by the value of the screen R's.
HEY. You might have helped me fix my 70's era cheapo Marlboro 1500B amp. The tone knobs made NO sense and made the sound terribly worse. I cleaned them (fixed scratching), I replaced caps on the board but no change. Then I reseated them and it's MUCH better. I still think a cap is bad or miswired (someone has definitely messed around in it before me) but it's much better now, so thanks!
I went back and looked when you had the top side up and wondered. maybe you have the same issue with this amp as you did with the Phaez amp you moved the transformer on. Marshall certainly moved theirs father apart on later amps. And this is certainly a much bigger amp power wise.
Any thoughts at to where the initial hum came from (which ‘disappeared’ when you discharged your test capacitor)? Could that have been a valve issue and the
I recognize those tubes. They're often marketed as "6p3s" Soviet mil-stock tubes. They're closer to 5881's than 6L6GC's. I doubt they're actual mil-stock.
@FMF Veteran not far off. If memory serves me the Sovtek 5881WXT’s are reproductions of the 6p3s-E, which is the mil-stock version of the aforementioned tube. Initially they had that coin base. I also recall that this 6p3s tube is also sold by Mesa as the STR-420 and again they insist it’s a 6L6GC equivalent.
Hallo thanks for your videos, they are very educationals but too long as this one. I think they would be easily to follow if they were shorter, no more than 20 minutes. It could be at least Part. 1, Part. 2. Enyways your are doing it great! Thanks again. Ben
It's been a while since I did this, but I'm pretty sure I did the caps. At the ery least I would have eliminated them. You're right, a faulty HT cap would give hum. It wasn;t that though.
Looks like you're just manipulating the symptoms running extra wires but the cause of the hum was never found.. the stock amp when new didn't hum and did not need those extra wires?? I would not be happy with this outcome at all
@@stuartukguitarampguy5830 Not blaming you Stuart, just putting myself in your situation... I don't think I would have handled it as well as you did.. I would be up at night. lol
I learn so much by watching you systematically diagnose these issues. Im learning it's all about a process of elimination. Please keep these videos coming. Thank you.
Excellent thanks for the feedback. It's interesting to how someone with 5 decades of fault finding experience can still (and often) scratch their head and say "What the $%^& is going on???"!
Brilliant video Stuart.
Thanks Dennis
I learned a lot today. Thank You.
Great thanks for the feedback.
This channel is so great and interesting! Thank you for sharing. Wish you were in the states. Have the same amp but reissue with the same hum 😂
Thanks Robert Hum is one of the most difficult issues to tackle!
Those are soviet 6n2p (20 watt 6l6) great tubes
You said you hoped this video was interesting, and you hoped that it wasn’t boring. Mr. Smith, all of your videos are educational as far as I am concerned. Tracking down a hum source or multiple sources is educational and I learn more times than not. I am not formally educated in elections, I learned what I know from online courses and from people like yourself. It is nice to have the benefit of someone like yourself and your experience to fill in the gaps of the knowledge that I have. If I was younger I would go back to school for electronics. I’m not what you would call old but I’m not young anymore either. I am retired in my late fifties, my son has a decent sized and reputable recording studio in Pittsburgh, PA. He is a professional touring musician as well. I do a lot of work for him as well as other musicians. I appreciate what you do, and please never think that it’s boring or too long. I use many diagnostic approaches from you. Thank you sir!! Lee
Thanks for the tip on the cleaner. For some reason your comment has not been added to this thread.
I don’t know why that happened. Hmm! I tried to send you a picture of the cleaner but it would not let me.
@@leecaruso5695 It's a complete pain tbh. If someone even mentions a website in a comment it gets pulled. Maybe it's something to do with preventing unwanted spam.
I don’t know but I do know how things have changed in a brief period of time. And I don’t think it’s going to get any better. Unfortunately. This cleaner is very good, if you try it I believe you will use it in stead of the other one with the god awful new design for delivery. Lol. I love what you do and I watch all the time. Thanks for spending the time to do what you do.
An easy way to determine the value of resistors in parallel using a calculator. Clear the memory, enter the value of R1, take its reciprocal, and add it to memory. Enter the value of R2, take its reciprocal, and add it to memory. Recall the memory, take its reciprocal, which is your answer. This works for any number of resistors in parallel.
For two resistors in parallel, the formula simplifies to Rtot = R1 x R2 / (R1 + R2), known as the ‘product over sum rule’. Incidentally, both the above methods result in 45.9 Ohms.
I always enjoy your videos but this one was especially informative for me with regards to grounding (earthing) schemes. I have built a couple of early Marshall 100 watt clones over the past few years; and while they do not exhibit a great deal of hum I think they can be better. This video has given me some pointers in the right direction I believe.
Excellent I'm pleased it helped. It was a learning curve for me too!
Another great informative video young Stuart!! (God! you must sleep at night dreaming of all these damn rotten amp problems!!) Thanks!
Yes I really need to get out more!
@@stuartukguitarampguy5830 ha ha!
Excellent job on the amp. I just repaired my Marshall DSL for a humming / crackling noise. Long story short, the new power tubes I put in were defective and it took a week of headscratching to sort it out. The problem was the tubes as I originally thought.
Sometimes that's how it goes🤷♂️
Well done!
Great video as always Stuart! on a classic amp from Marshalls early 100W history
That is remarkable! Great video, thank you.
Remarkable in terms of the ground routing........
Glad you enjoyed it Peter!
It's fascinating, extraordinary, now look, no hum.
I'm poking a little humor here, but I've learned when building amplifiers, it has been quite a lot better using aluminum chassis. Crazy stuff. Great video. Thanks, Cheers 😀
I took notes and wrote-down how to calculate the output power of an amp, thank you so much for that....cheers!!!!!
This hum issue can be so frustrating! I remember an instructor in an electrical class I was in years ago speak about how just the most minute length of wire +/- can cause EM crosstalk, Rf transmission , receiving,etc.. I have also in my own experience,been able to cut a few inches off of a guitar cable to stop it receiving radio signal. I have never seen something like you are dealing with here though. Wow! the same ground lug producing a different potential from one side to the other. That’s a head scratcher for sure. Great job getting that to a reasonable level.
Yes this one was a real challenge!
i nearly wet myself when the Zen music came on!
Your humour is so very British keep it up old chap.
I guess just a small amount of resistance to ground can cause hum. Maybe it's the type of circuit that determines its vulnerability.
Very good video.I think the best one on hum I have ever seen.Jimmy USA
Thanks Jimmy
That amp is in incredible condition (physically) for its age!
Very enjoyable video!! I am an amplifier nerd!!!
I'm glad you enjoyed it Jedi!
What a beauty, a mint '65 Plexi, worth a small fortune! Good work as usual Stuart
Another excellent repair..Hum is definitely a pain in the !!!..Great explanation, and info...Thanks for sharing..Ed..Herts..uk..😀
Hey Stuart. Just run a wire from the positive side of the PS caps so the owner can short it out on his guitar when it goes to humming. GRIN
Excellent idea! :)
Hard to tell, but if it’s an early Aluminium chassis, they were dodgy! Glad you sorted it! Cheers Stuart! Those had KT66 valves in them. That’s probably from 1965, in 1966 they went to EL34’s..
Yes I think it was now you mention it.
I wonder if converting the stock grounding system in that Marshall JTM45/100 to a Star-Grounding system will do anything to reduce the hum level?
I can tell you from experience that a poor connection between the pots and the chassis will cause an earth hum.
Simply undoing the pots and doing them up again can shut a hummy sixties Marshall up.
Sounds like nonsense, but it's a fact - and I do an awful lot of work on these old things.
Beautiful amplifier though Stuart.
I also always change the Bias caps because as you've said, if the voltage goes down, the Bias goes up and all hell breaks loose lol
Original valves would've been 6L6 or EL34.
You can tell what valves it should have in it by the value of the screen R's.
HEY. You might have helped me fix my 70's era cheapo Marlboro 1500B amp. The tone knobs made NO sense and made the sound terribly worse. I cleaned them (fixed scratching), I replaced caps on the board but no change. Then I reseated them and it's MUCH better. I still think a cap is bad or miswired (someone has definitely messed around in it before me) but it's much better now, so thanks!
Grounding everything to chassis is always a recipe for hum. It was a cheap way to manufacture, but a bad way to do electronics.
The number .707 is used because it just happens to be the Trigonometrical Sin-value for an angle of 45 degrees.
Awsome job.
Just another day in shop chasing electrons!
What happened to the HF oscillations ? or did I miss something.?
Hi Gary I can;t remember tbh!
I went back and looked when you had the top side up and wondered. maybe you have the same issue with this amp as you did with the Phaez amp you moved the transformer on. Marshall certainly moved theirs father apart on later amps. And this is certainly a much bigger amp power wise.
Interesting idea. If that is the case it was a design error.
Any thoughts at to where the initial hum came from (which ‘disappeared’ when you discharged your test capacitor)? Could that have been a valve issue and the
looks like a KT66
I recognize those tubes. They're often marketed as "6p3s" Soviet mil-stock tubes. They're closer to 5881's than 6L6GC's. I doubt they're actual mil-stock.
@FMF Veteran not far off. If memory serves me the Sovtek 5881WXT’s are reproductions of the 6p3s-E, which is the mil-stock version of the aforementioned tube. Initially they had that coin base. I also recall that this 6p3s tube is also sold by Mesa as the STR-420 and again they insist it’s a 6L6GC equivalent.
Hallo thanks for your videos, they are very educationals but too long as this one. I think they would be easily to follow if they were shorter, no more than 20 minutes. It could be at least Part. 1, Part. 2.
Enyways your are doing it great! Thanks again. Ben
Thanks for the feedback Ben, Its alwats a tricky issue as some people like longer videos and some shorter.
clipping the lead and adding the component is the wrong way to do it, those board are made to work on? looks like shit
I think you knocked the route of that ground to a different path that wasn't so noisy.....that was weird....lol
Why not change the old caps? Don't they contribute to a hum?
It's been a while since I did this, but I'm pretty sure I did the caps. At the ery least I would have eliminated them. You're right, a faulty HT cap would give hum. It wasn;t that though.
@@stuartukguitarampguy5830
Love your videos. Play more!
Looks like you're just manipulating the symptoms running extra wires but the cause of the hum was never found.. the stock amp when new didn't hum and did not need those extra wires?? I would not be happy with this outcome at all
Yes I agree. It was a VERY hard problem. I threw everything I knew at it and couldn't really get to the bottom of what caused the hum.
@@stuartukguitarampguy5830 Not blaming you Stuart, just putting myself in your situation... I don't think I would have handled it as well as you did.. I would be up at night. lol