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PostPosted: Thu Jul 20, 2017 1:18 pm 
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Location: Dawsonville, GA, US
petersch wrote:
Those 2 caps up top are the main power supply filters. The bigger they are the less hum and more power supply reserve you will have for peaks and transients. Making them a lesser value is the same as installing a smaller battery in your car, less reserved power. Bigger power supply filter should net you a blacker background with harder hitting bass.



AAAhh, ok
So the other 4 i replaced, i think they are filter caps?


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PostPosted: Thu Jul 20, 2017 8:20 pm 
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Location: Layton, UT, US
WCarson wrote:
petersch wrote:
WCarson wrote:
6SJ7's have a metal ring around the base. When i touch it while the amp is on i get a loud buzzing sound even with the volume off. I did not before


I did a test with another MP301 that was NOT modified and it did exactly the same thing, Buzzed when touching the metal base of the tube. I think it's safe to say this is normal operation as most of us don't listen to music touching the hot base of a Vacuum tube, LOL


Odd. Mine didnt really do that before. I was tapping for microphonics on a new set of 6Sj7 tubes. Its the same thing i did with my last pair, the red can type and a different set with a ring around the bottom. Very slight buzz out of the right side before. Now it sings if i touch it lol. No harm, but im always asking "why?"
That ring shouldn't be connected to any ground at all. Its just clamped around the bottom of the tube.
I checked the pin holes in the socket, all are seated fine.
EM? No i had all the lights turned off. Sounds nice and quiet now too.
Static? Should have discharged with a pop IF the ring even went to ground.
I tried with cheater plug and grounded. No difference.
Next time i dig around in it i will check and see if i missed something but if you say the other ones do it than ok.

What i am really trying to figure out at the moment is just exactly what the 2 caps i replaced on top do. We went from 180 to 470uF. Ive been looking at the simple diagram posted earlier.
What would happen if i changed it to a 330? How would it sound?


Tubes are microphonic components. putting your fingers on the metal base is transfering a signal from you to the tube and then getting amplified. Its no different than putting your fingers on the ends of input cables going into an amp. You get the same sound.


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PostPosted: Mon Jul 24, 2017 5:55 am 
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Location: toronto, ON, CA
Microphonic means literally operating like a microphone.... where the guts of the tube move ( like a microphone diaphragm ) say when you tap them. You'll can hear the tapping at the speaker. Such tubes are generally excited by the music pressure in the room, causing distortion.


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PostPosted: Wed Aug 09, 2017 7:30 pm 
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Location: Brampton, ON, CA
Reading thru 18pages of this mod and try to find out how can I get to the motherboard and daughter board, I still don't know how to disassemble the MK2 version.
After the tubes and the bottom panel removed , I can't see how I can remove the front panel, nor the the daughter board. Does anyone know how to or a link to youtube?

Thanks.


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PostPosted: Fri Aug 11, 2017 10:51 am 
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Location: london, ON, CA
MyLastWord wrote:
Reading thru 18pages of this mod and try to find out how can I get to the motherboard and daughter board, I still don't know how to disassemble the MK2 version.
After the tubes and the bottom panel removed , I can't see how I can remove the front panel, nor the the daughter board. Does anyone know how to or a link to youtube?

Thanks.


Did you get things figured out? You'll need allen keys to get the front panel off and to remove the screws on top of the amp holding the main board in place. There is a ground wire connecting the two boards. Be careful not to break it loose, or you'll have one more soldering job to do.

If you're new to tube amps, heed the warnings about the potentially high voltages inside. Be sure to drain the caps before you do anything else. Four hundred volts will really wreck your day.

Having said that, these mods are all quite easy to perform and are definitely worth doing. Good luck, and let us know how it goes.


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PostPosted: Fri Aug 11, 2017 5:41 pm 
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Location: Brampton, ON, CA
Thanks for the reply Lethargy. No I can't still. I removed the two screws on top, disconnect few wires and even removed the transformer on the board and can feel the mother board moving, i.e. can be lifted. However, the daughter board is blocking and seem to be unmovable. The front panel, are attach by screws from the inside, and I can only see 2 bottoms. There may some more.
I am comfortable with soldering and yes and I aware of the high voltage in the capacitor. The amp has been disconnected days now.


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PostPosted: Fri Aug 11, 2017 6:10 pm 
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Remove the 4 Allen Screws on the front panel and leave that other board attached to it. You'll need to unhook a few wires on the Daughterboard and the main board so PLEASE take a photo with your cell phone so you can re-assemble it correctly. If you have the mainboard screws and the choke removed you're 1/2 way there. I'll see if I have any of my pics available and post them up.

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PostPosted: Fri Aug 11, 2017 6:31 pm 
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That's odd, mine doesn't have screws in the front panel. Post few pics of the progress so far. Still stuck with the MB & the DB in place.


Attachments:
File comment: 2 visible inside screw
20170811_221947[1].jpg
20170811_221947[1].jpg [ 238.51 KiB | Viewed 566 times ]
File comment: inside MB & DB.
20170811_221817[1].jpg
20170811_221817[1].jpg [ 409.49 KiB | Viewed 566 times ]
File comment: Front panel
20170811_221723[1].jpg
20170811_221723[1].jpg [ 182.07 KiB | Viewed 566 times ]
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PostPosted: Sat Aug 12, 2017 6:22 am 
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Ah, now I see that the MK2 is much different than the MK3. I thought the big difference was between MK1 and MK2. My apologies for the inaccurate information.


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PostPosted: Sat Aug 12, 2017 6:41 pm 
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Lethargy, apologies is not needed. Your are trying to help, and I do appreciate that.


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PostPosted: Sun Aug 13, 2017 8:18 am 
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If you take off the volume knob and unscrew the pot, does it free the daughter board? You would think there's another screw or two at the other end, but maybe not. Somehow they had to put the amp together in the first place and it doesn't make sense for a manufacturing standpoint to make access to the screws too difficult.

Edit: I just remembered that user "bikenut" posted pics of his Mk2 on the first page of this thread and talked about replacing some resistors. Maybe you could PM him to see how he got the board out.


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PostPosted: Sat Oct 07, 2017 11:08 am 
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Lat Word, did you ever do the mods to your MP301?

Reason I ask is I'm doing another 301 for someone else and I went back to read the thread.

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PostPosted: Wed Oct 11, 2017 4:45 pm 
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peter,

Yes I did. The daughter board is attached to the front panel from the inside/bottom by 4 screws to hold the volume and power button (I think).
But access those screws are next to impossible. What I end up doing is removed the 2 large capacitors on top (since I am replacing them anyway), also removed the wires attached to the daughter
so that the main board can be tilted and lift out. I also have to mind there are 2 soldered white wires and a plug (3 wires) attached to the main from the daughter board.
A lot of works to:
- replaced 2 large caps.
- replaced 2 blue (22nf) caps since 1 of them burned.
- remove to by-pass C6/C6A filtered caps.
- replace 1 bottom caps.

After of these are done, now no more humming but I found the output volume quite low for my liking. Now I wonder if I go back and put back those 2 C6/C6A caps would restore the output volume.


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PostPosted: Wed Oct 11, 2017 5:00 pm 
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Wow, lots of work indeed.

The volume lowering is usually quite minimal and will make normal listening around 9-10 O'Clock instead of 8 O'Clock. To each their own but yes, Should you re-install C6/6A it will restore your volume and over driving back to what you are used to. Removing the 2 capacitors only slightly lessens the drive signal to the output tubes resulting in a lower noise floor and less clipping. Just be aware that those 2 capacitors are polarity sensitive and must be installed in their original orientation. Should you get them in backwards be prepared for a snap and some shredded paper strewn all over the inside of your amp.

Good luck and thanks for sharing your experience with others in the thread.

Pete

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PostPosted: Tue Oct 24, 2017 8:27 pm 
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Stevedlu wrote:
Peter do you know what the two blue 250v 150uf caps do? I replaced them since they look like low quality chinese generic caps with https://www.digikey.com/product-detail/en/panasonic-electronic-components/EEU-EE2E151/P13649-ND/1245978. It is a high quality panasonic cap, the improvement in detail to the top end and imaging in quite profound indeed. If i had a choice to replace these or the coupling caps i would choose these. Panasonic makes some impresive caps and it only cost $7.50! Digikey is out but they can be had on ebay for the same price.


Steve, I finally got around to trying your Panasonic caps in C8/8A, very nice improvement! These are the Cathode bias resistor bypass capacitors for the power output tubes. They are across the 300 Ohm 5W bias resistors and provide a good AC ground for the Cathodes on the power tubes. I noticed the upper mids are a bit more defined and separated, before the sound was more congested. I also ordered up a set of JJ KT77 from Jon @ The Tubestore, what a great sounding set of tubes !! The bottom end tightened up and the mids also seem more balanced and the top end in conjunction with the Panasonic cap upgrade makes a significant difference. These are only first impressions as the new components have less than an hour on them, I can hardly wait for them to settle in a bit more. :D

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