Monoprice 15 Watt Tube Amp-Mic and Direct

[rio]

I've done a fair share of tube rolling, but in a lazy non-tech sort of way.
But I will say that IMO the V1 position is the biggest tone changer, and that a good old NOS 5751 in V1 is just great in so many amps.
If you are messing around beyond that, might as well look at some upgraded power tubes as well just for kicks.

JJ's, Tung-sols, Tads, NOS, . . . it's all fun, but it's a deep rabbit hole for sure

I got JJs just because they’d arrive at the same time as the amp but I’d like to find NOS tubes. Good to know regarding v1 havingthe biggest impact - thanks for the info!


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[lawson-stone]

I got JJs just because they’d arrive at the same time as the amp but I’d like to find NOS tubes. Good to know regarding v1 havingthe biggest impact - thanks for the info!


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The hilarious irony is that you can spend more on the tube rolling than you spend on this amp! But it's so much fun. Something about this amp just makes me want to experiment.

[Longways to Go]

That is very true! Some dudes seem to get addicted to it.

I kinda stumbled into tube rolling because I bought a couple of pawn shop amps that just happened to have expensive NOS glass in them. I eventually sold the amps, but kept the good tubes! When I had a VHT Special 6, I really got into trying out the various sounds. Eventually, I got tired of piddling around and got back to putting my time into practice. But I did discover the NOS 5751 along the way. It's been my go to ever since. The amps may come and go, but I don't sell my favorite tubes.

[rio]

The amp arrived today - schools and many businesses were closed due to snow but UPS not only delivered but delivered early.

This amp has no right to sound this good at this price and that’s even before the tube swap. The replacement tubes should arrive before the end of the week and I think I’ll have a chance to record with it on Sunday but so far just in my living room I am THRILLED with how it sounds with my L5.


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[lawson-stone]

The amp arrived today - schools and many businesses were closed due to snow but UPS not only delivered but delivered early.

This amp has no right to sound this good at this price and that’s even before the tube swap. The replacement tubes should arrive before the end of the week and I think I’ll have a chance to record with it on Sunday but so far just in my living room I am THRILLED with how it sounds with my L5.


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That's a common reaction judging from other forums I've cruised reading discussions about this amp. All your tube replacement will do is buy you some more headroom and the 5751 gives a sweeter tone somehow, hard to describe (might be my imagination). For a "Fender" vibe turn the EQ mid knob down to 1 or 2, bump the T and B up, put the tone knob on about 6 and find the spot on the gain where the break-up comes when you really dig in. It's a pretty decent tone. Not a 65 Princeton Reverb, for sure, but a very fine and respectable warm, tube-clean tone.

[murrayatuptown]

I thought I posted here, but maybe there is another Monoprice thread.

A friend asked me about this, and after replying with a bunch of crazy ideas about buying TWO, one for a 'control sample', and one for lab rat experiments, I calmed down, said there was a one-year warranty, to let it live in peace for a year, and ordered ONE (he had already moved on to other amp shopping research).

While awaiting it, I contacted someone for a reminder what beefier iron higher-fi OPT I had discussed with him a year or so ago. He mentioned one aimed at being a replacement for Dynaco ST35, with UL PP EL84. He had a specimen with the UL taps incorrectly located, as I didn't intend to use the UL taps. They are labeled & taped off & the transformer is en route to me, arriving two days after the Monoprice victim (I mean amp).

I only listened to the noise level with no instrument, and note that it is better than the Vox-Bruno TB35C2 I dragged in last week (retired, looking for a new 'job' in the house).

I think I will let a friend use it for a while to see how far it falls short for him of his late 60's Princeton grail tone. I always wanted to see how close actual pentodes could get instead of 6V6's (really only because the sockets are already there). I have another amp of his I got side-tracked from modifications of so a loaner would be a polite thing to offer.

There is plenty of room for the larger output transformer. I thought there was a filter choke on the schematic but I didn't see one quickly looking inside with a flashlight. I have a suitable one I might consider adding...eventually.

I should probably figure out why the Vox-Bruno is so noisy before tormenting the new arrival, since that doesn't involve violating a warranty. I like to type the name Stage (F)right incorrectly and hope I have to apologize for the insult.

I see the schematic for this has two different cathode resistors (1500 and 820 ohm) on the first 12AX7 preamp, in a configuration books often call a differential amplifier if both are used. Some amps do not use the 2nd one, and just ground one grid. At first glance, I am not sure I can name an amp that has this configuration but I look at the schematics pretty quickly & save them somewhere, never to be seen again. Some Marshall's parallel two triodes with one having a cleaner configuration (lower value cathode resistor) and the other looking like a 'cold clipper' (higher value cathode resistor). I'll have to revisit this & see if it's a subtler form of this approach.

I haven't looked much at Blues Junior circuitry because my friend has the Pro Junior, and doesn't like the Blues Junior. So all my study of the PJ schematic has ignored the Blues Junior. Someone mentioned that somewhere in comparisons (possibly for lack of other things to compare to).

Interestingly, the manual says when changing tubes/valves, to use the same type, but there are no markings on any of them other than likely date codes like a T048 and a (forgotten) letter and 018. The 12AX7's look 'stubby' to me, but I didn't have a marked on in hand to compare.

Murray

[murrayatuptown]

My mistake...too many schematics on the table & not enough sleep.

The Laney 12R does NOT have dissimilar cathode resistors in a diff amp configuration at V1. That is in the Vox-Bruno TB35Cx.

The Laney 12R (and Monoprice, by visual inspection) do NOT have a filter choke in the power supply.

My Monoprice/SR 15 W has plenty of hum to know it's working and I do not detect any reverb effect with a 'cheater' footswitch (a 1/4" TR cable plugged in and center of plug open or touching ground).

The amp doesn't seem to have a lot of gain...or I have a low output humbucker on the guitar I had in the living room. More evaluation needed.

[murrayatuptown]

Kind of like a girl you enjoy dating but likely wouldn't marry...

Or vice versa...

[murrayatuptown]

The amp I got on a stack of whims sounds fine, but I can't engage the reverb by trying to 'fake' a switch by grounding an extra guitar cord plugged into the reverb footswitch jack. I do not hear any reverb. I'll try to find a footswitch and 1/4" T-R plug in the basement.

Meanwhile, I wrote to Monoprice tech support to confirm what the correct location of the red and white connectors on the reverb tank are (to make sure mine weren't assembled reversed). They didn't know but will find out.

Time elapses...

I bought a cheap foot pedal today because it made more sense than what my Plan A. was. The reverb works. It's subtle, which is good enough for me. Maybe it's signal-dependent and playing with more dynamics (& confidence) would produce more effect. But subtle I prefer.

[bluenote61]

Fwiw, this amp is available in Europe at Thomann under his own brand "Harley Benton". But as always with those cheap mass products, you can get a good one as well as a bad one...