Musical Paradise MP301 MKIII: Tube Load Lines and Bias
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- Опубликовано: 31 май 2024
- In this segment I show you guys how to draw load lines and what to look for as far as biasing a triode driver tube. I think I found a great place to setup this 6SJ7 tube triode strapped and it should have enough gain to drive an EL34 type tube! I need to order some parts so might be a week or so before we get back to this so please be patient!
I was sent this amp to test and review from @intoitreviews
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Thank you for the extensive explanation of load lines. I love this channel because there is no audiophile bullshit, just facts and useful information. I am an electrical engineer but I was born much later than the time when tubes were used and I learned a lot here. Keep it up good work. Greetings from Croatia 🇭🇷
This is my favorite kinds of videos you make. The most knowledge is hidden here.
Yes yes ! Have to dig all over the net..lol
I've owned the MKII version of this amp for more than a decade. Your video got me to pull it off the shelf and start playing with it. It had been running 5881 power tubes and 6SJ7 driver tubes for a very long time. Can't recall how I landed on that combo. Today rolled in a pair of Gold Lion KT77s and they hum pretty bad........way more than the 5881s. I can hear a little hum with the 5881s, but the KT77 hum makes the amp unlistenable.
Nice!! Great to hear doggie is doing better... 🙂
Yes, thank you
Good points about the load lines 😄
Great video. I now have a better understanding of how load lines are used in the design process. Would be interested in seeing a video on how you go about selecting transformers.
You got it!
Yet another great video!
Its good learning, especially the load lines and also the resources you're using on the net like the cathode bypass cap calculator.
Any chance of a video that runs through what you've found useful on the Internet and also your setup (multi meter, scope etc)?
Love your work Skunkie!!
before buying the A10 this one was on the list, I even paid it but got an email from the guy owning the company making the musical paradise (that was just after the covid was breaking out, in march 2020) and he told me that due to the situation it might take some months to get it and i chose to have a refund. turns out that it was a good idea to get the A10. anyway, when it comes to schooling and showing how the vacuum tubes related things are done you have no equal on youtube. you are, simply put it, the best
Thanks!!
@@SkunkieDesignsElectronics, any given time
So far this is exactly what I'd hoped for. If I wanted a cheap tube power amp, I'd buy an MP301 then do the Skunkie mods, probably for about $600 all in with the replacement Edcor output transformers.
Reisong A10/A12 was much easier to mod and the results are really spectacular. I think you can find a second hand for 200-250
This was an especially good video. Getting more deeply into the theory of tube electronics, and even how to use certain audio based calculators, seems like something a lot of people are looking for. I know I enjoy and appreciate them. It’s even more effective when working on a circuit design with a good amount of issues. Thank you, Stephe! 🔊😊🎶
Glad it was helpful!
@@SkunkieDesignsElectronicsStephe, that was absolutely brilliant - not just helpful. It wasn’t too technical at all (especially as you watch it back over a few times if you get stuck on the theory or the practical implementation). This is exactly what we would need to do whether designing or checking a a design for ourselves, so I’m really grateful. I’ve read worked examples of working out load lines plenty of times. but I’ve never designed any circuits - so that was all just theory for me in the past which makes it hard to remember. This was super interesting and useful, especially after following along to understand why this amp was performing as it was to begin with.
One quick question if I may - When you re-worked the load line, using the 33k plate resistor for the driver tube, to get the bias current raised to where the tube is performing both in a more linear region of the curves, and also where the signal voltage swing (at 4Vpp, 1.4VRMS) becomes symmetrical (as it should be). Did I miss something, but the original bias point was at 6V, then on the revised load line you went from a bias voltage of 4V (at 08:49 in the video), so the signal swings down to -2V and up to -6V instead. Was that a small oversight, or did the other changes you had worked out also shift the bias point down from 6V to 4V? Or would we now need to make changes to the bias resistor to change it to 4V instead? I suppose where the load line ended up, swinging from 6V down to -4 and up to -8V would still have been symmetrical anyways, so no problem either way I guess, but it would be helpful for my understanding to just sanity check that please. Thanks again, Steve 👍 [Edit: Just watched it back again and I think I’ve messed up - the voltage on the Cathode is/was at 6V, so the bias point must be slightly more negative than that shouldn’t it? So maybe the first load line signal spread should have been from a bias point less than 6V? It’s late and I’m confused 🤯😂 - So if you could just clear this up please that would be a great help 🤞. Thanks again]
I easily could has said one phrase wrong. The original bias point was -6V and so the input grid would swing from -4 to -8. The revised bias point is -4 and would swing from -2 to -6. The plate load resistor moved the load line up out of the "heel" of the curves, the cathode resistor changes the bias point to a more linear part of the load line. Hope than clears this up.
Hi Stephe, No you didn’t say the wrong thing at all - It was just me having one of those ‘brain fart’ moments! 😂 I watched it all again and of course it makes total sense to shift the bias point down slightly from 6V to 4V to get a 1.4VRMS signal right where it needs to be where the swing each way will give a symmetrical output - which was of course the whole point - Doh! 🤯 Silly me. It was a bit late on a night when I first watched this and I kinda got all muddled up in my head and fixated on the wrong principle. Thank you again for clarifying and all your hard work 🙌
It's pretty complex stuff but once it clicks it's like "Ah ok, NOW I get it!!" And there is a little trial and error to find the ideal spot plus these curve charts are a guideline, sometimes in practice you have to play around some to get the voltages where they need to be.
Yeah this series is really interesting! Keep going :)
Glad you enjoy it!
Really great video! I love the more technical videos you do with load lines and how to set bias points. One really interesting video could be how to cathode bias a tube via LED/diodes. I feel like I have a good understanding of how to bias a tube via a more traditional resistor and bypass cap. How to select the right LED and resistor in series I have never been able to quite figure out. Anyway, thanks for all the great videos.
Stephe... Good video. Well done.
Thank you!
Great video Stephe. I love these dives too
Thank You, great Work.
Excellent video. Would love to see more on technical topics like this!
Very interesting, thank you very much!
Glad you enjoyed it!
Excellent videos and explanation!
Can you go over going over the load lines for the output tubes, also in PP arrangements at some point?
Thanks!!
I recently did a video on output tube load lines. Honestly there is an easier way to figure out what output transformer to use etc. I'll go over that with this amp. Honestly, I'm still learning how to deal with PP stuff, not something I fully grasp fine tuning yet.
Can you imagine if MP had their act together? That would not result in good videos like this one :)
lol yes, thank you MP for making a mediocre product lol
hi stephe you can polarise cathode with a potentiometer 5k and a scope seeing sinus equal positive and negative on the scope ,its more easy to do than polarisation curves shematic
That sounds harder to me!
Thanks for that run through, I finally got my head around using those curves. One thing that occurred to me about the LF cut off bypass capacitor value. They may have curtailed it to prevent the small output transformers saturating and distorting too much?
These honestly aren't that small, they are the same size core as the 15W Edcor transformers. The only reason they would saturate is if they are defectively designed. Remember they advertise 15Hz - 30KHz frequency response.
@@SkunkieDesignsElectronics Well, that range sure appears rather fanciful, but maybe it's at +/- 20db :)
Loving this! I have two that I will definitely mod once the results are finalized. Stephe, this channel is excellent. I love your approach and content. Greetings from Perth, Western Australia! I may have to start saving for one of your amps. Would you build one in 240v?
Most electrolytic caps have an actual capacitance a bit larger than the marked value. Film caps, not so much.
Finally REAL SHI..T
The video at 2:00 mark, is that schematic with your changes in green is all one needs to modify this to be correct?. Your load lines and your choices especially the 220uf cap in the cathode of EL-34 you say it's 330uf is better to go with the 300 ohm resistor bypass. Where is the finished final changes for this amp? Thanks
That is NOT the final changes, I say this multiple times. I have some other projects and reviews as you have seen being published, plus have some parts ordered. PLEASE be patient!
Looking forward to it Steph.