I respect your work ethic and professionalism. I watch because you do not take shortcuts and you find and resolve all the issues. Old world craftsmanship. Thank you Sir for the education.
So, I am gonna take a minute and say THANK YOU Lyle! I learned two awesome things today from this video! 1) I am understanding how to use Ohms Law properly, and this walk through help reinforce this skill! 2) I learned I can measure voltage drop across a resistor with my DMM with the two probes. I did not know I could do this in "real time" the way you did it with the probes on either side. VERY cool! I have an impossible time learning through the "Socratic" method, my brain has never worked that way. I need to be shown, and walked through puzzles before I can learn, apply, and reinforce the information. So these types of videos are PERFECT for how I learn. I thank you so much for taking the time and making the effort to teach! This helps and excites me in a way that only furthers my desire to get better and better at fixing and building amps! I thank you again!!!
I'll latch on and say thank you for consistently putting up videos on the issues you face with amps every day. I know it takes time out of your repair schedule to share your knowledge with us. I have learned a TON about amps by sitting on your shoulder and hearing what you're doing as you improve the various circuits. Looking forward to 2022. Cheers!
Curran, since you are still learning this stuff as you go, it's also worth noting that the voltage drop (and therefore the wattage and heat dissipation) across the resistor R7 was being measured *at idle* here, with no signal passing through the amp; the voltage drop would likely increase at least a little if somebody played through the amp at high levels, and so the resistor would be dissipating even more wattage and heat. In a cathode biased amp such as this one, the difference in dissipation from low volume to full volume (ignoring the switchable power scaling) might be fairly minimal because such amps are often biased into Class A operation, with high current draw even at idle (tubes might already be biased at 90 to 105% of their dissipation ratings!) and so the power supply voltages run pretty much the same regardless of how hard you are or aren't pushing the amp ---- but in a fixed bias Class AB amp, that resistor would definitely drop more voltage and run sugnificantly hotter when the amp is pushed hard. You could clip the ohmmeter leads onto the resistor, play a loud power chord, watch the voltage drop increase, and calculate the dissipation with Ohms law. A good exercise for learning! And, as always, be careful and stay safe!
Thank you, sir! Had problems with an Origin 50 that (turns out) needed the same ground wire added to the output board per that service bulletin you mentioned. Would not have known about it without your advice. Thank you again!
Seems like the origininal power tubes eye just rated at a higher cathode current per plate voltage. Marshall may have not realized that could occur even with self bias. Higher wattage resistormade sense in this scenario. Would have been interesting to see the diff in cathode current between the original and new power tubes.
If this was a more valuable amp I might have taken the time to see what exactly was the current draw. But I needed this thing fixed and gone. Could have been screens, could have been plates. I can't defend Marshall here, because even with "good" EL34s that 2W resistor had 2.1W dissipation at idle. Amp Design 101 says use a resistor rated for twice the power needed.
Yup. Although Fender usually used a choke inbetween the main B+ to the output tube plates and the screen-supply node, in many/ most other amplifier brands It's typical to see a simple dropping resistor in that same part of the circuit (drops a few volts and limits current to the output tube screens). The choke adds additional filtering and provides better voltage regulation, but the choke costs FAR more than a resistor does, takes up a fair bit of space, adds weight, and can't be ---- or at least should not be ---- mounted directly to the PCB. As to which Marshall's of the past have historically used a choke, I can't speak, since I've not worked on any, though I've worked on plenty of Fenders with chokes. Most other vintage combo amps ---- Valco, Danelectro/Silvertone, Ampeg, Magnatone and so on, don't use a choke. Fun fact: on really old amps with field-coil speakers that don't have permanent magnets, the electromagnet coil of the speaker also acts as a filter choke!
Interesting that 6.5 watt is what of years where rated at 5 watts. Thus the Dale cw-5 . The mass is high however the resistor does survive way over current very well. They are wire wound by the way they will glow red if you over current them enough and they do survive . Do not ask how I know . Cheap infrared temp gun at harbor freight helps about 15 dollars.
While the resistor might survive being run at well in excess of it's wattage rating, the excess heat will break down the solder joints, overheat the adjacent components (drying out capacitors etc), and perhaps carbonize the board to the point of becoming conductive.
WOW! I'm seriously contemplating buying the combo version of this amp but these videos are scaring the crap out of me. What version/revision of design is this particular head, and are the newer ones "improved"?
You can see the board revision number in the video. I don't know if there are any differences in production years. Note that I am only discussing the Origin 20. The 50 is a different circuit and I don't know that it has these or any problems. Haven't had one on the bench, don't like to speculate.
I put a 15w 150 ohm resistor in there when I burnt mine out. Though, tbf, I was experimenting, had just reassembled the amp, but hadn't connected the HT lead firmly, it wasn't really on.... ooppps...
@@PsionicAudio Ah, fair play, you're right, I looked back on the invoices, it was a 5w, as I couldn't find a anything else in stock at the time..... ;-) Well, I figure it's gotta hold up better than a 2w.
Temping-in a 200 ohm resistor might have been a happy accident. A little less current but considerably more voltage across it = more power dissipation. A 150 ohm resistor might not have discolored so quickly. You might not have recognized the need for new tubes and how you were exceeding the power rating until this amp found it's way back to your bench for the eventual failure?
Yup. Well, faulty tubes, but you should never design with components right at the edge of their capability. Should have been a 5W resistor. Then the fuse could have prevented any component level repair. See the upcoming video on another glaring design flaw of the Origin 20.
All just my opinion...but Marshall, the once mighty Marshall that made rock and roll history in a gigantic way, has fallen so far from what they used to be. Poor design and cost saving shortcuts. There are MANY Marshall “clones” that blow away Marshall current offerings as far as workmanship and tone goes.
Silly video. First if the buyer or viewer is expecting a hand wired boutique style build at this price point, I call the idiot rule. Second if a player cant make this amp sound good or "Marshall" as they say , take some lessons.
I respect your work ethic and professionalism. I watch because you do not take shortcuts and you find and resolve all the issues. Old world craftsmanship. Thank you Sir for the education.
So, I am gonna take a minute and say THANK YOU Lyle! I learned two awesome things today from this video! 1) I am understanding how to use Ohms Law properly, and this walk through help reinforce this skill! 2) I learned I can measure voltage drop across a resistor with my DMM with the two probes. I did not know I could do this in "real time" the way you did it with the probes on either side. VERY cool! I have an impossible time learning through the "Socratic" method, my brain has never worked that way. I need to be shown, and walked through puzzles before I can learn, apply, and reinforce the information. So these types of videos are PERFECT for how I learn. I thank you so much for taking the time and making the effort to teach! This helps and excites me in a way that only furthers my desire to get better and better at fixing and building amps! I thank you again!!!
I'll latch on and say thank you for consistently putting up videos on the issues you face with amps every day. I know it takes time out of your repair schedule to share your knowledge with us. I have learned a TON about amps by sitting on your shoulder and hearing what you're doing as you improve the various circuits. Looking forward to 2022. Cheers!
Curran, since you are still learning this stuff as you go, it's also worth noting that the voltage drop (and therefore the wattage and heat dissipation) across the resistor R7 was being measured *at idle* here, with no signal passing through the amp; the voltage drop would likely increase at least a little if somebody played through the amp at high levels, and so the resistor would be dissipating even more wattage and heat. In a cathode biased amp such as this one, the difference in dissipation from low volume to full volume (ignoring the switchable power scaling) might be fairly minimal because such amps are often biased into Class A operation, with high current draw even at idle (tubes might already be biased at 90 to 105% of their dissipation ratings!) and so the power supply voltages run pretty much the same regardless of how hard you are or aren't pushing the amp ---- but in a fixed bias Class AB amp, that resistor would definitely drop more voltage and run sugnificantly hotter when the amp is pushed hard. You could clip the ohmmeter leads onto the resistor, play a loud power chord, watch the voltage drop increase, and calculate the dissipation with Ohms law. A good exercise for learning! And, as always, be careful and stay safe!
I come for the amps, but I stay for the pie recipes.
Sir, I love your videos. How I wish I was your neighbor so I could learn from a true craftsman. Your work is outstanding. 👍💯
Thank you, sir! Had problems with an Origin 50 that (turns out) needed the same ground wire added to the output board per that service bulletin you mentioned. Would not have known about it without your advice. Thank you again!
Stress sheets and design reviews should expose the over disipation of individual components.
Cool video, nice instruction and tech info..Fab as usual Lyle..Ed..UK..😀
R13 seems to be missing some solder on one pad..
Very interesting....
When your amp is designed by your accounting department to save five cents on a 2W vs 3W resistor
Seems like the origininal power tubes eye just rated at a higher cathode current per plate voltage. Marshall may have not realized that could occur even with self bias.
Higher wattage resistormade sense in this scenario.
Would have been interesting to see the diff in cathode current between the original and new power tubes.
If this was a more valuable amp I might have taken the time to see what exactly was the current draw. But I needed this thing fixed and gone.
Could have been screens, could have been plates.
I can't defend Marshall here, because even with "good" EL34s that 2W resistor had 2.1W dissipation at idle.
Amp Design 101 says use a resistor rated for twice the power needed.
R7 is a series resistor instead of using a Choke?
Yup. Although Fender usually used a choke inbetween the main B+ to the output tube plates and the screen-supply node, in many/ most other amplifier brands It's typical to see a simple dropping resistor in that same part of the circuit (drops a few volts and limits current to the output tube screens). The choke adds additional filtering and provides better voltage regulation, but the choke costs FAR more than a resistor does, takes up a fair bit of space, adds weight, and can't be ---- or at least should not be ---- mounted directly to the PCB. As to which Marshall's of the past have historically used a choke, I can't speak, since I've not worked on any, though I've worked on plenty of Fenders with chokes. Most other vintage combo amps ---- Valco, Danelectro/Silvertone, Ampeg, Magnatone and so on, don't use a choke. Fun fact: on really old amps with field-coil speakers that don't have permanent magnets, the electromagnet coil of the speaker also acts as a filter choke!
Interesting that 6.5 watt is what of years where rated at 5 watts. Thus the Dale cw-5 . The mass is high however the resistor does survive way over current very well. They are wire wound by the way they will glow red if you over current them enough and they do survive . Do not ask how I know . Cheap infrared temp gun at harbor freight helps about 15 dollars.
While the resistor might survive being run at well in excess of it's wattage rating, the excess heat will break down the solder joints, overheat the adjacent components (drying out capacitors etc), and perhaps carbonize the board to the point of becoming conductive.
WOW! I'm seriously contemplating buying the combo version of this amp but these videos are scaring the crap out of me. What version/revision of design is this particular head, and are the newer ones "improved"?
James, watch Part 3 on this same amp; you'll likely be dissuaded from buying one.
You can see the board revision number in the video. I don't know if there are any differences in production years.
Note that I am only discussing the Origin 20. The 50 is a different circuit and I don't know that it has these or any problems. Haven't had one on the bench, don't like to speculate.
Yes the first batch that were built had issues (one year) and were recalled by Marshall , the newer ones are improved .
the bean counters may have modeled the amp usage as very seldom being run at FULL power, so 2W was good enough! Typical bedroom user might be AOK!
I put a 15w 150 ohm resistor in there when I burnt mine out. Though, tbf, I was experimenting, had just reassembled the amp, but hadn't connected the HT lead firmly, it wasn't really on.... ooppps...
I can't imagine the lead diameter of a 15W resistor fitting the pad on the board.
@@PsionicAudio Ah, fair play, you're right, I looked back on the invoices, it was a 5w, as I couldn't find a anything else in stock at the time..... ;-)
Well, I figure it's gotta hold up better than a 2w.
Consider making 5 hr videos.🌟🌟🌟🌟🌟
Temping-in a 200 ohm resistor might have been a happy accident. A little less current but considerably more voltage across it = more power dissipation. A 150 ohm resistor might not have discolored so quickly. You might not have recognized the need for new tubes and how you were exceeding the power rating until this amp found it's way back to your bench for the eventual failure?
ohm, ohm on the range.........
So a bad design is at fault here?
Yup. Well, faulty tubes, but you should never design with components right at the edge of their capability. Should have been a 5W resistor. Then the fuse could have prevented any component level repair.
See the upcoming video on another glaring design flaw of the Origin 20.
@@PsionicAudio do these design flaws apply to to the origin 50H as well?
All just my opinion...but Marshall, the once mighty Marshall that made rock and roll history in a gigantic way, has fallen so far from what they used to be. Poor design and cost saving shortcuts. There are MANY Marshall “clones” that blow away Marshall current offerings as far as workmanship and tone goes.
Silly video. First if the buyer or viewer is expecting a hand wired boutique style build at this price point, I call the idiot rule. Second if a player cant make this amp sound good or "Marshall" as they say , take some lessons.