A Guitar And Gear Support Forum

Here is a video of me playing with a Monoprice 5Watt Tube Amp. Only $120!

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I have one of those, I like blasting it when nobody’s home, lol




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Kewl!
I love my 15 watt monoprice tube amp!

I have one of those. Pretty sure I've spent more swapping tubes than I spent on the amp, but it's great. I love it for my pedalboard.

Here is another video I did with my Monoprice tube amp!

[media] [/media]

aullucci wrote:I have one of those. Pretty sure I've spent more swapping tubes than I spent on the amp, but it's great. I love it for my pedalboard.

Were you able to find better tubes than the stock ones?


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SXLuvr wrote: ↑Sun Jun 27, 2021 1:39 am

aullucci wrote:I have one of those. Pretty sure I've spent more swapping tubes than I spent on the amp, but it's great. I love it for my pedalboard.

Were you able to find better tubes than the stock ones?


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FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

I have one of these from when they first came out. Gave it to my son but it somehow ended back upstairs in the room over the garage.

Partscaster wrote: ↑Sun Jun 27, 2021 7:50 am FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

Interesting, as the same type article is posted many places, yet it tells you nothing really. A 12AX7 "may" have a gain of 100, but that is in theory. Typical Fender circuit with the typical Fender resistors (which sets the bias) gives you a gain of 51. You need to study and comprehend the datasheets to see how they differ, not only gain but current, plate resistance etc.

90 % of the amps out there use these exact resistor values and have copied this circuit since it came out. Stick a 12AT7 in there, you are now not using the right resistors that the tube is capable of (mis-biased). Gonna sound like shit. Use the proper resistors and you can get more gain than the tamed 12AX7, yet that is never done. Circuit has to be optimized for the tube being used, anything else is just a crapshoot or a poor excuse.

A 12AY7 will bias closer to optimum using 12AX7 bias resistors. Fender used that tube a lot in V1, when they changed to 12AX7, they left the resistors the same.

A 12AT7 is good for driving the output tubes, i often use one in the phase inverter and many times i get more total output wattage than a 12AX7 would provide, basically just how blackface Fenders did it.

Another thing the article doesn't even mention, new tubes are garbage. Go get old tubes, not Ebay but find a old radio, record player, or reel to reel and gut it. GE, RCA, TUNGSOL, SYLVANIA, MULLARD, etc.etc. Those are the tubes you want.

Partscaster wrote:

SXLuvr wrote: ↑Sun Jun 27, 2021 1:39 am

aullucci wrote:I have one of those. Pretty sure I've spent more swapping tubes than I spent on the amp, but it's great. I love it for my pedalboard.

Were you able to find better tubes than the stock ones?


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FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

Thanks for the link to that article, Partscaster, it increased my “tube knowledge” a lot


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mozz wrote:

Partscaster wrote: ↑Sun Jun 27, 2021 7:50 am FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

Interesting, as the same type article is posted many places, yet it tells you nothing really. A 12AX7 "may" have a gain of 100, but that is in theory. Typical Fender circuit with the typical Fender resistors (which sets the bias) gives you a gain of 51. You need to study and comprehend the datasheets to see how they differ, not only gain but current, plate resistance etc.

90 % of the amps out there use these exact resistor values and have copied this circuit since it came out. Stick a 12AT7 in there, you are now not using the right resistors that the tube is capable of (mis-biased). Gonna sound like shit. Use the proper resistors and you can get more gain than the tamed 12AX7, yet that is never done. Circuit has to be optimized for the tube being used, anything else is just a crapshoot or a poor excuse.

A 12AY7 will bias closer to optimum using 12AX7 bias resistors. Fender used that tube a lot in V1, when they changed to 12AX7, they left the resistors the same.

A 12AT7 is good for driving the output tubes, i often use one in the phase inverter and many times i get more total output wattage than a 12AX7 would provide, basically just how blackface Fenders did it.

Another thing the article doesn't even mention, new tubes are garbage. Go get old tubes, not Ebay but find a old radio, record player, or reel to reel and gut it. GE, RCA, TUNGSOL, SYLVANIA, MULLARD, etc.etc. Those are the tubes you want.

This post also increased my “tube knowledge.”

In the 3-page manual I have for my Monoprice amp, they recommend that if you need to change out the tubes in the amp, that you use the same type and preferably from the same manufacturer.

Any idea why they recommend that?


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Probably liability. Chances are they only tested it with tubes that are in current production, for UL testing. (lots of chinese stuff is not UL listed) There are also other compatible tubes that draw more current than stock so i'm sure everything would run hotter and possibly burn out the power transformer, they don't oversize anything as copper cost money.

mozz wrote:Probably liability. Chances are they only tested it with tubes that are in current production, for UL testing. (lots of chinese stuff is not UL listed) There are also other compatible tubes that draw more current than stock so i'm sure everything would run hotter and possibly burn out the power transformer, they don't oversize anything as copper cost money.

Thanks for the reply, mozz, I appreciate that.


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mozz wrote: ↑Sun Jun 27, 2021 7:21 pm

Partscaster wrote: ↑Sun Jun 27, 2021 7:50 am FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

Interesting, as the same type article is posted many places, yet it tells you nothing really. A 12AX7 "may" have a gain of 100, but that is in theory. Typical Fender circuit with the typical Fender resistors (which sets the bias) gives you a gain of 51. You need to study and comprehend the datasheets to see how they differ, not only gain but current, plate resistance etc.

90 % of the amps out there use these exact resistor values and have copied this circuit since it came out. Stick a 12AT7 in there, you are now not using the right resistors that the tube is capable of (mis-biased). Gonna sound like shit. Use the proper resistors and you can get more gain than the tamed 12AX7, yet that is never done. Circuit has to be optimized for the tube being used, anything else is just a crapshoot or a poor excuse.

A 12AY7 will bias closer to optimum using 12AX7 bias resistors. Fender used that tube a lot in V1, when they changed to 12AX7, they left the resistors the same.

A 12AT7 is good for driving the output tubes, i often use one in the phase inverter and many times i get more total output wattage than a 12AX7 would provide, basically just how blackface Fenders did it.

Another thing the article doesn't even mention, new tubes are garbage. Go get old tubes, not Ebay but find a old radio, record player, or reel to reel and gut it. GE, RCA, TUNGSOL, SYLVANIA, MULLARD, etc.etc. Those are the tubes you want.

This is a lot of good information. I went the NOS route for tubes, too. I wasn't looking for anything exotic and I haven't gone tube shopping since so I have no idea where current prices are, but I got 2 GE 12AX7, a GE 12AT7, a 5751 (I don't remember the brand, maybe Sylvania? Westinghouse?) and 2 Raytheon 6V6 over the course of a couple of orders. I do think overall I spent more than I spent on the amp. One of the GE 12AX7 sounded clearly best (to me) out of all my preamp options but I couldn't tell the difference between the two 6V6 in the power section. Both were slightly better than the stock tube, but they were indistinguishable from each other and for me changing the power tube had a lot less effect than the preamp tube. I will say I was going specifically for a clean, pedal platform type amp - I don't crank it for distortion, and I specifically picked tubes that had clearest sound a lowest noise, so take that into account when thinking about how you use yours...

aullucci wrote:

mozz wrote: ↑Sun Jun 27, 2021 7:21 pm

Partscaster wrote: ↑Sun Jun 27, 2021 7:50 am FWIW, here is an interesting Reverb article about preamp tube changes and tone.

https://reverb.com/news/how-to-improve- ... tube-swaps

Interesting, as the same type article is posted many places, yet it tells you nothing really. A 12AX7 "may" have a gain of 100, but that is in theory. Typical Fender circuit with the typical Fender resistors (which sets the bias) gives you a gain of 51. You need to study and comprehend the datasheets to see how they differ, not only gain but current, plate resistance etc.

90 % of the amps out there use these exact resistor values and have copied this circuit since it came out. Stick a 12AT7 in there, you are now not using the right resistors that the tube is capable of (mis-biased). Gonna sound like shit. Use the proper resistors and you can get more gain than the tamed 12AX7, yet that is never done. Circuit has to be optimized for the tube being used, anything else is just a crapshoot or a poor excuse.

A 12AY7 will bias closer to optimum using 12AX7 bias resistors. Fender used that tube a lot in V1, when they changed to 12AX7, they left the resistors the same.

A 12AT7 is good for driving the output tubes, i often use one in the phase inverter and many times i get more total output wattage than a 12AX7 would provide, basically just how blackface Fenders did it.

Another thing the article doesn't even mention, new tubes are garbage. Go get old tubes, not Ebay but find a old radio, record player, or reel to reel and gut it. GE, RCA, TUNGSOL, SYLVANIA, MULLARD, etc.etc. Those are the tubes you want.

This is a lot of good information. I went the NOS route for tubes, too. I wasn't looking for anything exotic and I haven't gone tube shopping since so I have no idea where current prices are, but I got 2 GE 12AX7, a GE 12AT7, a 5751 (I don't remember the brand, maybe Sylvania? Westinghouse?) and 2 Raytheon 6V6 over the course of a couple of orders. I do think overall I spent more than I spent on the amp. One of the GE 12AX7 sounded clearly best (to me) out of all my preamp options but I couldn't tell the difference between the two 6V6 in the power section. Both were slightly better than the stock tube, but they were indistinguishable from each other and for me changing the power tube had a lot less effect than the preamp tube. I will say I was going specifically for a clean, pedal platform type amp - I don't crank it for distortion, and I specifically picked tubes that had clearest sound a lowest noise, so take that into account when thinking about how you use yours...

Thanks for this post, Aullucci, it’ll help me out if I ever need to change out the tubes in my Monoprice.


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I do agree that tubes make a difference, but it's more of a fine tuning tool. I found that V1 is wired in reverse, i.e., the second half (V1B) is the first preamp stage. The second half (V1A) is the driver stage. Another difference from most other amp designs, is the volume is between the two halves of V1 and the tone is after the driver. Typically, I've seen the tone and volume between the two halves or the tone in between and the volume after. Note I say typically, because most of the topography has been as I've described, it doesn't mean there aren't any other designs like this.

Now when replacing V1 you will affect both the preamp gain and the driven signal to the output tube. You loose gain and some power tube gain and volume. For the lowest preamp gain while losing the least amount of power tube gain/volume, you can use a 12DW7(ECC832). The 12DW7 uses a 12AU7 in the first half of the tube, with a 12AX7 in the second half. With this amp that tube would drop the power tube gain/volume, while maintaining the preamp gain. JJ Tubes make a reverse 12DW7 called the ECC823, where the 12AU7 is in the second half and the 12AX7 is in the first. This will give you the lowest gain in the first stage preamp (V1B) and the full drive (V1A) to the output tube. I did this on my Fender Pawn Shop Series Greta to clean it up as much as possible (it's still a dirty girl).

download/file.php?mode=view&id=6889
Note the schematic is the first gen (TV Front) with two input jacks for 5w and 1w. The 1w switched jack was replaced with a push button when they converted to the second gen front mount controls. The switch or switched jack bypasses the V1B cathode bypass cap resistor.

The biggest change of tone comes from changing the speaker. To my ear, the stock speaker (which is pretty good to begin with) give a more British Flavor. I swapped in a WGS G8C, which gave it a little more of a Fender flavor. To me it's like something between a Tweed Princeton and a BF Champ. I do like playing mine through my 1X12 cab with an Eminence JS-1250 for a big bold cleans to a great dirty tone.

Odd way of using the low input, disconnects the cathode bypass cap so just lowers the gain.