Started having issues with it shortly after the warranty ran out. Signal would cut out. I found a temporary fix by plugging a patch cable in the effects loop. Now there's a very loud buzzing sound and no signal output. Definitely a preamp failure. Now I have a tube amp that no technician is going to want to work. I don't think I want to spend the money on replacement tubes which may or may not fix the issue. I was never impressed with the tone of this amp to begin with. Too dark and flubby. EQ is terrible. Drive section is too harsh and completely unusable. Worse with bright switch on. Don't bother with buying this one.

This is a great amp! I thought I'd be swapping both the speaker and the tubes, but the amp came matched JJs in the power section and Ruby pre-amp tubes ...I did swap speakers because I had a Celestion G12T-75 spare that was already broken in ....it's a rock n roll machine right out the box! No way you're going to find a better amp for this kind of money!

Pros:
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Value - these features at this price point... I think only Monoprice and Thomman do that

Decent build quality; everything feels solid, not flimsy

Separate volume/EQ for clean/drive channels - this is important, especially since there is a great volume difference between the channels

Quiet for a tube amp (no annoying buzz/hum at idle)

Reverb and FX loop

JJ tubes (YMMV)

Sounds great (once I figured it out - see cons)

Cons:
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Not sure if this is a con but because it brought me days of frustration I am putting it under cons. This speaker/cab combo has the most directional sound projection of all the combos and cabs I've had. I spent days trying to get the amp to sound clearer but no matter how much I twisted the knobs it never sounded clear. I even swapped the speaker but it still had that same "wet blanket over the speaker" muddy sound... until I accidentally discovered that if I point it at my head it completely changes the sound, like someone removed the wet blanket. This is true of all combos and speaker cabs but the change it makes for this amp is really the most drastic I've experienced so far. I now play it tilted up and it sounds great! I was about to put it up for sale as I got frustrated chasing the clarity but I am glad I discovered this as it made me keep the amp. I play it every day now :-)

Not real cons but rather nit picks:
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The drive channel does not have the character of its little StageRight 15W brother amp - overdriven tone is a bit generic but overall good.
Presence control would be a great addition.
The knobs and switches are tiny, even for my small(ish) hands.

I am very happy with my purchase. Are there better amps out there? Well, of course there are but "for the money" the SB12 is a glowing 5 stars. When I say "for the money" don't get the impression this amp will leave you longing for more but is "acceptable" considering the price. No, this is an excellent sounding, feature-rich amp. You could definitely spend a lot more and get less!

o I appreciate having separate EQs for both dirty and clean channels. The tone controls are quite sensitive allowing for a lot of control and adjustment
o The clean tone is great, nice and thick just as a tube amp should sound. I was using a Fender Mustang III V2 previously and was never happy with the digital synthetic tone. Not so with this amp. Much, much better!
o With 50 watts there is plenty of headroom.
o The dirty channel isn't to my liking because the overdrive comes on too strong and fast. A gain level set to '2' is already too much for my personal preference.
o The 2-spring reverb tank is weak. It is servicable but even when maxxing out the effect is not full and vibrant. I changed the tank out for a 3 spring model and it made a huge difference.
o I am withholding judgement on the Celestion Seventy 80 speaker because it has not yet been broken in. For now the tone is a bit dark for my liking but this might remedy itself over time. I did try an older Celestion GT12T-100 that I had in a spare cabinet and liked the tone better. Time will tell on the Seventy 80.
o The amp's build quality is very good overall. When I changed out the reverb tank I had to remove the screws holding on the lower backing plate. I was a little disappointed to see that the assemblers had not drilled pilot holes for the screws but instead went straight into virgin wood which caused the wood to split. It still holds okay and doesn't rattle but, still, a little disappointing.
o My amp came with the JJ tubes which are good quality.
o I am not sure if the line out is balanced output. The literature doesn't specify and I think that it should.

This is my first tube amp. I have a Boss Katana and a Spark. I have only been playing for 3 years, but I am in a band that performs live. I have been using one of the band members Marshall DSL4 CR 40 Watt amp. I just went through the break in period and finally attached my pedal board. The cleans are incredible. I have only been playing with gain the last 2 days with and without by board. I am really happy. For under $400 this amp is equal to $1000+ amps. I highly recommend this amp if you are looking for a high quality tube amp for a great price.

This amp is very satisfying and has way outperformed expectations. It's a genuine steal at this (on-sale + discount: $308) price, and can't think of anything reasonable to criticize. The sound, right out of the box and before burn-in, is fantastic. Love the combination of controls and input options, and agree with other reviewers that the clean channel is a great match for pedal junkies. May upgrade the speaker with another Celestion 12" I have laying around, but for now it's not worth getting out the screwdriver until it's broken in and I've played with it enough to tell where I want to take it.
It's basically a Laney LC-50, for less than an old, well-used LC-50. Great basic tube circuitry that sounds great to my ears. Monoprice, kicking butte... ignore the haters.

This totally kicks! There is a lot of headroom in the clean channel and the dirty channel goes from mild distortion to high distortion. So there isn't really that "edge of breakup" type of thing built into this amp. But a nice overdrive pedal into the clean channel will get you there. The construction is fantastic. The sounds that I get out of this are just lovely. No complaints here at all. Well worth the price.

I'm no guitar wiz, in fact barely a bedroom hack but... 50 watts of tube amp is, I'm sure, way overkill for my needs. All that that being said, this is definitely a 'big boy' amp!

Cosmetically it's georgeous. It just looks like a very serious amp.

I also have the SR 5 watt tube amp and a Fender Mustang LT 50 to compare it to and it just kills. I like to pair it with the 5 watt SR (with the volume balanced) to give me a 'surround sound' effect. The master volume makes this very easy to do. I generally play through the clean channel with pedals for distortion and added effects so I'm sending the same signal to both outputs.

The bright switch on the clean channel gives it some very nice boost/chime (if that makes any sense?) The clean channel delivers great tones with or without adding distortion via the pedals, and the drive channel just flat rocks! You don't need any OD pedals to get terrific crunch and distorted tones, just tweek the gain knob to achieve your desired effect.

I don't know enough to really address the reverb, I just have it maxed and have no complaints. Having seperate EQ for both channels is a great feature as well as the effects loop, which I also haven't really used yet since I'm usually sending the same signal to another amp that doesn't have the effects loop and want to get the same effect from the pedal board on both sides, but again, a terrific feature to have.

Bottom line, I can't imagine getting a more high quality and high value tube amp for anywhere near the price point.

This is probably the best deal you can find in the World.

I know that is a very profound statement, but dollar for dollar, you can not find an amp that is made with real wood, JJ tubes and more.
Just watch a very much liked review from Darrell Braun Guitars from the link below. Darrell knows how to really give a review like no others. Subscribe to him to get the best Monoprice reviews.
https://www.youtube.com/watch?v=uWGyGmBck-g

This a great amp and a great value when you compare it to the main brands. Its clean channel is very nice with a little of that tube punch we like. Reverb is good and the drive channel is nice and bluesy. You won't find a better amp at this price