Stephe, this is why we follow you. Honesty, intelligence, vast knowledge and a scientific validation. Great video

What fun! Stephe's doing what she does best and I'm enjoying every minute of it.

Impressive what improvements you made in such short time. Thumbs up! Also great and clear to read schematics that you're sharing. Double thumbs up! 👍👍

Well Stephe, I’m astonished at how quickly you not only came up with those improvements, taking the performance in the right direction, but that you did that and was also able to put together a brilliant video explaining what you did, and why that worked in such a clear and helpful way. You’re a legend. I’m very impressed and can only thank you for putting yourself out to do this so well and so quickly, especially as not so long back it looked like you would have preferred to just toss it out the window and move onto some of your other more pressing commitments! 🤣 Glad it didn’t involve totally gutting this thing and after all, and it essentially came down to a few bad decisions that had wiped out the bass response and totally distorted what little was left in the bass region. Still makes me question whether all these Musical Paradise units should be marketed as being ‘capable’ of running such a crazy wide range of tubes in them. I don’t know if this amp has the switches in it that the others they make (which it turns out are to change the heater voltages) to broaden the range of tubes each circuits ‘can’ work with) - but as you’ve ably demonstrated, just because tube pin layout and heater voltages MAY make it ‘capable’ of taking a different tube, that is NOT the same as claiming such a broad range of tubes will actually perform WELL as alternatives; that of course depends on individual tube specifications which specifications the circuit was DESIGNED to work around to produce great sound. It’s a nice idea to give wide flexibility (and also let folks learn in the process) but it would be better to have a smaller suggested list of tubes that could perform well, instead of trying to be a jack of all trades and master of none. Learned a lot today. Looking forward to watching and understanding any further refinements. Thanks again 🙌

Wow! Great work Stephe. Skunkie strikes again!

I am so happy to see this. I was about to buy the MP-301 and then panicked when I saw your first video, but, what you can do to tube circuitry with provable results is so impressive, I plan to still get the MP-301 and make your mods. Fantastic work.

This is a great clean up. I am really enjoying this series.

Hi Stephe. Triode curves for 6SJ7, you got 'em. Refer to the flash drive I sent you. PDF Files => Tube Data => 6SJ7 => 6SJ7 GE. Triode curves are included for this pentode. Hope this helps.

Looking forward to your continued work on this amp.

Howdy. Comprehensive evaluation. And Yeah. The input tube should benefit from some neg. feedback. If the sensitivity suffices one might consider omitting the input tube cathode capacitor. That would provide neg. feedback of the input tube. Or one might consider splitting the cathode resistor into two parts and only capacitor bypass one resistor. Someone might consider using a trimmer and connect the slider/viper to the bypass cap. to obtain tunable gain vs. neg. feedback. But Yes. Skunkie does not like trimmers as they are troublemakers. Point taken earlier. High Regards.

Stephe- 1st I'll say from my many years in this industry that you'll always have the folks who think they know something, and don't and then there are those who just like "shit sound" (let them eat cake)... it doesn't matter!! Keep doing what you do as no one likes to hear, pardon the pun, that their baby's ugly... Price doesn't always equate to performance and measurements will only take you so far. One who is trained to listen would never buy or setup 1/10 of the craziness I've seen and I have a database of hundreds. I will say that my reference system has never had a bad comment and has blow away most (recording engineers, symphony players and conductors, as well as audio manufacturers (all for under 15K, not including treatments)!! No sub/s I don't have a big enough room.

Very informative video. Really looks like it improved the amp quite a bit . Really brings back a lot of memories from when my uncle had a radio repair shop..

Hi Steph, Great Job as Usual.!! Hey a triode strapped 6SJ7 is essentially a 6J5 tube. With an amplification factor of around 19 and an RP around 7600 ohms. Thanks, Mark

That's a nice upgrade so far

Hi Stephe.. Good to know that you found out that there’s an inadequate Ck value for the output.. I would personally go a tad lower with ~270uF to 330uF in that position just for more subjective ‘weight’ in the presentation.. I hope the lispy sibilants would get resolved with further mods down the road..

+1 for an assessment of the tube dac. I've had it for a fews years, sounds great to me. Always interested in improvements.

HI, I'm admiring, that's great!!

Nice work.

A Lampizator Tube DAC clone would be worthwhile It is apex level

Looks like a confused design mistake with the switching of the voltages on the tube, great find - also worrying about global negative feedback, is that really valid - I mean, did you ever hear anything negative from a well designed negative feedback design? I mean these THX amps sound great to me. Anyhow, very cool as always. About the voltages, could it also be due to wanting the amp to be able to use as many different tubes as possible(which of course isn't ideal...)?

Thanks Skunkie! very interesting and informative. Wait to see more. Do you think that this amp could be more interesting than the Muzishare X7, which you have said a lot of good things about and without it being subject to modification?

Kazoo Sound! I’m dying. 😂

Hi , good work . I will apply yor changes.

The high screen voltage, somewhat higher than the anode voltage ( in the past era was also a standard used operation design ) it is and was used often correctly a ....LITTLE bit.... higher than the plate voltage ( unlike as seen in this amp , this is starving point operation and gives high gain but also HIGH distortion )...that was practice and normal used design with pentodes to expand the curves and the dynamics as well as amplification............. To document this starvation mode oeration .....( MULLARD UK -Tube manufacture -EL34 and other original famous nos tube ) ....They had such a low power and LOW-FI design.......for radio and simple amplification without any HIFI asiration........to be able to do direct coupling without a capacitor between the driver anode ( EF86/6267) and the grid of the output tube.. The result were not up to quality music reproduction but the amp was CHEAP to build !!

Would be interesting if you tested the pre amp and dac from this company.

Thank You, Thank You, Thank You (😘) for your work Stephe, you've given me hope that I can get decent sound out of my investment! I don't mind if I have to outlay a conservative amount of money for Edcor xformers (four of them for my two units) to gain much better fidelity, I'll do what it takes. Have your experiments lowered the 60hz noise floor (hum that you heard) or is that a product of the PS? One last thing... Can you please supply a BOM for the replacement parts you're using? I live in the middle of nowhere and parts acquisition can be extremely tedious to say the least. With the BOM I can order top tier items from one source and be done with chasing everything down which leads to revisions done in a more timely manner.

With the screen and plate voltage inverse does the screen now become more of a plate or does it just destroy quality all together ?

Nice ............; This kind of operation point on the penthode driver input is called a ( Starving mode operation ) ..sometimes seen in vcertain very old amplifiers. Question : Was this design made for driving speakers or headphones because with one secondary winding you have to choose ......and the other oints were you put the finger on problems are designed by ...hmmm.... OPT is probably questionable quality and the UL here does not make any sense for headphone drive of a n EL34 .............;also pure class A of this tyube type is standard 250 plate ...........triode mode should be used ( dedicated for HPhones).....plus the tandem pentode input/driver followed by Triode for coherent harmonic musical spectrum ..... Voltage on the screen of the penthode is better choosen by lower value of about 112 volt ... operation conditions of the plate voltage must also be adapted etc........... there's a lot of work to do and mayber you can get it sing ..... The cap on the screen ( 6SJ7/5693) must be of quality ... It would be interesting also to see the design of the power supply ...... Good luck and you will find ways to improve this thing within the limits of the amp and opt . kind regards. ( Personaly I would mayb consider to use this amp/chassis to build a quality stand alone powersupply for a preamp or a phono stage ...........if the transformer is good enough ) PS....With a single pentode ( per channel )like a c3m, a 717A/6AK5/408A WE ....one can build a VERY good headphone amplifier..........Yamamoto build some very nice headphone amplifiers and preamplifiers with sope of these pentodes...........and they sound realy very good. In this case very interesting to see what you can get out of this design .....

Any chance of you trying out the mp tube dac? Ive heard nothing but good things about it.

Those square waves are not flash - what components are used to filter the AC power supply?

cool

20% tap is perfect for a 6V6, UL you'll get a really good four watts.

Ever had a look at an Elekit?

The original circuit is a classic circuit, from the time of the advent of pentodes. Works great in the normal power range. Why do you need to add feedback? Add odd harmonics and make your amp sound harsher? Well, the power will decrease a little, but the sound will definitely get worse. We know, we went).

So KT88 tubes are not recomended for this amp by any means (pwr trans will fry otherwise) , as I understood today from the new video. Will it happen in case of such schematic changes only? Is there a reasonable modification route to keep these tubes or better not in order to have better sound with mods you are deciding to follow?

I wonder if the earlier versions had the same incorrect components and design or were these issues introduced over time?

Although I have absolutely nothing to do with tube amplifiers until the first tube-based DSP is finally available, I still like to take a look at your videos now and again out of interest. Your posts on the MP 301 are currently being discussed in the German community of tube enthusiasts. I wanted to form my own opinion and watched your videos. I noticed - regardless of the technical content - that there are hardly any critical comments on your views. Statistically speaking, this is an outlier and particularly noticeable in the context of the debate here that I know of, in which the pros and cons of the MP 301 are almost equally divided. Have there been no critical comments on your videos, or are they all so disrespectful that it would be better to delete them?

What I dont get is how did MP get it so wrong .I hope their Preamp is not the same...

510k grid leak resistor is too high. It might cause el34 current drift. Any thoughts?

😃

How is your doggie doing?