So!
I've been testing this amp all day. You know that semi-wasted feeling you get when you have been noodling and tweaking all day? (raises hand) Mix that with the smell of new tubes and mexican paint burning in, and this has been a pretty good day. The last day of vacation.
I have the 5150 on top of my Ironheart 60H, with the Peavey XXX cab in stereo 8Ohm. The 5150 is feeding one side, the IRT60h is feeding the other side. This is a pretty fair test as both amps are 2x6L6. I'm trying to figure out if one amp blows the other away, if the new amp has better sounds or utility than the old amp, etc. Euge Valorvita, in his review of the Ironheart 60H said that it sounded like a 5150 to him and I didn't understand that at the time, but the amps have some definite similarities but also some differences.
When I was testing earlier with the 5150 as a preamp into the Ironheart, I noticed that both amps have about the same "size" and presence. That is to say that neither amp feels bigger or smaller than the other, and the presence knob on both amps seems to have about the same range of adjustment and effect. IOW, when I would run the 5150 preamp into the Ironheart power section, I would have to set the presence about the same to get the same sound.
Note: I have to give this review relative to my current amp because thats the best way to describe the strengths and weaknesses, given that I will be using them the same way; as a lead guitar amp and as a hard rock/metal rhythm amp.
So what I've been doing for the past three hours is plugging my Guitar (Ibanez with Steve Vai Evo HSH set) and SD1 into one amp. Then putting it on standby and plugging into the other amp. Back and forth, back and forth. I've been trying to get the absolute best lead guitar sound on one amp, then trying the same on the other amp. Then I've also tried to emulate each amp with the other. I've been doing this on the red/blue channels and the lead/rhythm channels on both amps. So four channels in the comparison.
The first main caveat, is that if I was unable to use a boost, I would sell the Ironheart and the 5150 would be the clear winner, end of contest. But the second caveat is that after testing, I found that the 5150 also benefits from the boost for tone shaping and I prefer the 5150 with a mild treble boost from the sd1 and just a touch of gain. So its not a cut and dried win for the 5150 because I would be using a boost with either amp.
I was able to find the SD1 setting that works well on both amps. With the Ironheart, I'm running it at its maximum practical gain, with some extra gain and tone shaping from the SD1. With the 5150, I use the extra gain and tone shaping from the sd1 but back off the gain (to about 10 o clock) on the red channel (blue channel near max gain.)
Each amp has something I'm striving to get more of. The 5150 needs more controlled aggression. The Ironheart needs a bit more saturation. So now let me focus on the 5150.
The 5150 actually doesn't seem like it's voiced for metal. It has a smoother top end than I anticipated (that is similar to the Ironhearts lead channel, but lacks the british rawness of the irt rhythym channel.) Both the red and blue channels have similar smooth top, and in fact when tremolo picking its easy to imagine Eddie's fast picking in Eruption solo. The XXX cab is a smooth top speaker, so I think the evh cabinet or G12T75 marshall cab would give some extra bite. But neither the blue or red channels have Marshall rawness. (The Ironhearts "rhythm" channel does have the aggressive "british" top end.)
The amp has an overabundance of mids, in fact on the red channel it almost seems designed to cut the mids, and it will still sound "up front". (In general I found that cutting EQ works best and most of the controls are south of noon.) So on the red channel, the mids are close to zero and the treble and bass are somewhere in the 3-5 range. Mids can be boosted, but it will give some honk and maybe undesirable qualities. It doesn't need much mids though.
There is good interplay between the presence and treble and you have to decide where you want the presence, you can trade some bite for some openness.
The blue channel is a little different. It seems to be designed that when you boost the mids it gets fuller but not the same honk. Like maybe it has a broader push. This is a smoother channel and the eq seems to have more freedom. With extra gain from a boost, the blue channel can be made to sound virtually identical to the red channel. The red and blue channels have a similar top character, but the mids/eq are voiced and work different.
Both channels have an "up front" effortless quality, even when you lower the gain. These channels have a mid push or mild compression that puts everything in the foreground, even if you lower the gain. So on both blue and red, by lowering the gain you can get some in beween, note bleed rhythm sounds. My opinion, is that even without a boost, the 5150 doesn't respond as well to volume knob as did the Friedman IR-X, but, you can get a variety of gain levels by switching to single coils and/or just changing the channel gain.
Overall, the 5150 has that ultimate saturation for lead guitar that makes it liquid and fluid, but it doesn't sound quite as articulate as the Ironheart. And the Ironheart has a mid character that is more aggressive or "marshally", but could also sound thinner or not as pushed. With the 5150 the high end notes are thicker, but don't have quite as much edge or "zing". But take the boost pedal away from the Ironheart and this isn't even a competition. But as I said, I prefer the 5150 with the SD1. The 5150 gets some extra zing and tightness from the boost, the Ironheart gets more saturation.
The 5150 has an exceptionally low noise floor. Boosting the Ironheart with the SD1 does not create a ridiculous Ola Englund level of "will it chug" noise, but it is more than the carefully manicured 5150. But this is probably because some of the upper frequencies have been tamed in the 5150, and why I am generally seeking more aggression.
The Ironheart has more features, a wattage/mv, front mounted res/pres, front power/stdby, switchable clean boost (which is invaluable for when you have an "always on" boost like the SD1) toggle switches for all selections, and a more versatile eq section with push/pull pots. The Ironheart lead and ryhytm channels are a good bit different than the blue/red on the 5150, with the rhythm channel having that british aggression you don't get with the 5150. It doesn't have any midi and imo it needs something like a Voodoo labs midi switcher.
The 5150 has the best noise floor, and doesn't need a boost pedal for liquid gain. There are compromises in the layout and front panel buttons, but it has midi which makes up for some of the compromises, and the 5150 could be integrated into a 4cm mfx rig with different boost levels synced with midi channel switching. It has a smooth top that reminds me of Eddie's tremolo picking in Eruption, so to my ears, it has rock guitar voicing even though I know its a metal staple. It probably would probably get more aggro with different speakers, but it will probably never have the Marshall kerrang.
After a full day of testing I am happy with it but not blown away. I think the pushed/compressed notes lend themselves to better lead guitar playing, but its also lacking some top aggression and eq control that I am used to. Also no master volume.
I will probably play it throughout the week and see if I have any epiphanies. It just sounds good without a boost and is more of a plug and play kind of amp. I know the Ironheart well and how to coax the needed saturation out of it, but ultimately it doesn't do it quite as well. I need to convince myself of this before I am completely happy with the 5150, but the 5150 just is missing some rawness and flexibility that may take some time to adjust to.
may I suggest reading the manual? Lol. 
