Results of tube upgrade on Monoprice 15W amp - wow.

kmckenna45

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I have posted before about my Monoprice 15W amp. Most recently - I sold a guitar, so I was thinking about finally selling the Monoprice 15w - and buying a Fender Deluxe Jr. However, last month I ordered two new JJ EC83S and two Ukraine-made EL84's. So, I put them into the Monoprice - and WOW.

My criticism of the Monoprice was always it's lack of growl. The new tubes definitely help with that. I can't imagine another amp under $600 sounding this good.

Suprisingly - the tubes that I removed from the Monoprice 15W (built in 2020) were ALL JJ tubes! I expected cheap chinese knock off tubes, but they were all JJ's. I replaced them anyway and am very happy.

One question for those of you tube-heads (Which I say with admiration) - the JJ tubes I removed have a second line under their model number. Two are labelled EL 84 12JO, and the others ECC83S 1910

What does the 12J0 and 1910 refer too? I'm wondering if these are less expensive versions of the EL84 and ECC83S, that conform to the specs - but aren't of the same quality.????

thanks,
 

Matt Sarad

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My brother bought one and it was unusable.
Monoprice replaced it with a new one.
He replaced a tube.
I use it a rehearsal rather than hauling one of my amps.
I love it!
 

MuddyWolf

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Those other numbers on the tubes are probably lot numbers or something. JJ power tubes are good. JJ preamp tubes can be dull sounding. I don't use the preamp tubes. I prefer shuguang 12ax7b.
 

Wound_Up

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I have posted before about my Monoprice 15W amp. Most recently - I sold a guitar, so I was thinking about finally selling the Monoprice 15w - and buying a Fender Deluxe Jr. However, last month I ordered two new JJ EC83S and two Ukraine-made EL84's. So, I put them into the Monoprice - and WOW.

My criticism of the Monoprice was always it's lack of growl. The new tubes definitely help with that. I can't imagine another amp under $600 sounding this good.

Suprisingly - the tubes that I removed from the Monoprice 15W (built in 2020) were ALL JJ tubes! I expected cheap chinese knock off tubes, but they were all JJ's. I replaced them anyway and am very happy.

One question for those of you tube-heads (Which I say with admiration) - the JJ tubes I removed have a second line under their model number. Two are labelled EL 84 12JO, and the others ECC83S 1910

What does the 12J0 and 1910 refer too? I'm wondering if these are less expensive versions of the EL84 and ECC83S, that conform to the specs - but aren't of the same quality.????

thanks,

They're standard JJ tubes. Nothing about them is different than any other JJ tube of the same model
 

VintageSG

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The JJ EL84 are quite good. The 6p14p-EV from the old Soviet Union are very good.
Nice to see a move toward JJ.

You'll get more mileage from swapping out V1 in terms of different sounds. The JJ 5751 is a very good V1. It isn't as 'gainy' as a 12AX7, so the gain control has a greater effective sweep. It'll still go crazy, but it takes more rotation of the control to get there.

If you can change the valves out, can you rebias too?. In my experience, most fixed-bias amps come set with a rather cool bias from the factory. It makes good commercial sense. Longer valve life, plus if the valves do drift towards the 'warm' end, there's some leeway. To get to a ballpark figure, you just need one multimeter and a keen sense of self preservation. The latter is as important as the former.

Get the chassis out, plug a dummy load into the speaker out or ensure the speaker is connected. This is very important. The amp must have a speaker or load connected.
Turn everything to zero. Go make a brew. This gets everything toasty.
Using the pot 'TR1', adjust until the voltage at the junction of R13&R28 reads -12.5V and yes, that is a minus voltage.
Do -not- stick your fingers in there.
Preferably use a non-conductive screwdriver, or at least an insulated one.
Power it down and leave it for half an hour before refitting the chassis. This lets the high voltages drain from the filter caps and the valves to cool down. Still, don't stick your fingers where you wouldn't stick your gentlemenveg. Zapping oneself is considered bad form.
Enjoy.
 

FMKeller64

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Got one of these heads a few weeks ago, changed the all the tubes, some no name brand, slovtek EL84 - Tad 7025 in the V1, V2 V3 Tungsol 12AX7, quiet no hum, smoothed out the gain , like it better than using a 5751, I like to tube roll my Bass Amps, so I a few tubes lying about for testing
 

Vibroluxer

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There's great news and bad news about getting old tubes. Old organs are filled with just the type we need. Bad news is, we usually have to take the entire organ to get the tubes.
 

Tom Hicks

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The JJ EL84 are quite good. The 6p14p-EV from the old Soviet Union are very good.
Nice to see a move toward JJ.

You'll get more mileage from swapping out V1 in terms of different sounds. The JJ 5751 is a very good V1. It isn't as 'gainy' as a 12AX7, so the gain control has a greater effective sweep. It'll still go crazy, but it takes more rotation of the control to get there.
I put a JJ 5751 in V1 of my '58 Gibson GA6 to get a touch more usable sweep on the volume knob before I run out of clean. Its a nice tube.
 

redhouse_ca

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I have posted before about my Monoprice 15W amp. Most recently - I sold a guitar, so I was thinking about finally selling the Monoprice 15w - and buying a Fender Deluxe Jr. However, last month I ordered two new JJ EC83S and two Ukraine-made EL84's. So, I put them into the Monoprice - and WOW.

My criticism of the Monoprice was always it's lack of growl. The new tubes definitely help with that. I can't imagine another amp under $600 sounding this good.

Suprisingly - the tubes that I removed from the Monoprice 15W (built in 2020) were ALL JJ tubes! I expected cheap chinese knock off tubes, but they were all JJ's. I replaced them anyway and am very happy.

One question for those of you tube-heads (Which I say with admiration) - the JJ tubes I removed have a second line under their model number. Two are labelled EL 84 12JO, and the others ECC83S 1910

What does the 12J0 and 1910 refer too? I'm wondering if these are less expensive versions of the EL84 and ECC83S, that conform to the specs - but aren't of the same quality.????

thanks,
That's interesting. I have the 5 watt (which i confess i am not a fan of) and swapped the 12ax7 with a bunch of vintage and quality new(ish) tubes and it didn't make a huge difference. I don't know much about the 15w but ill check it out. I did mod mine by adding a 50k variable negative feedback pot and that helped, and I tried it through a different speaker/cabinet and that was also a lot better, but I have been disappointed with it, given how much people seem to like it.

Cool that you have had a good experience with yours and that the tube roll made it even better!
 




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