Got a Blackheart BH5H for cheap not too long ago. NAD thread here. I got it specifically to mod it. I had already modded my Marshall DSL15H a little bit. But, wanted to go a little further on the Little Giant, and make a good Amp better. The goals were to fix the small weaknesses in the amp, change the tone into the Marshall camps, boost the gain a little, make it more versatile, and reduce the noise. WARNING - Modding an amp like this can be dangerous. Lethal voltages can be found in the caps and kill you. The BH5H will normally drain the caps via the bleeder resistor r13, after the amp is disconnected from power. But, you should double check with your meter on both sides of R14. IF r13 is damaged or becomes open, it may not be draining the charges. In that case one can make a simple discharge tool (some wire, alligator clips and a large ohm ( > than 100K ) and high voltage ( > 250V) resistor. SO, Replaced the existing on/off switch with a 3-way switch to add a Standby mode. Lot of the components are rated at the no load voltage off 400V. But, the voltage drops once the tubes are heated to as low as 283v at the preamp caps. So, Standby switch will help lengthen the life of the amp. Lot of folks convert the amp to just pentode or triode mode and use the switch to do standby. But, I wanted to keep the pentode/triode, because the two modes are noticeably different in tone. With the other mods, wanted to keep that. So moved it to the back, and fitted a Carling, double pole, triple throw switch (off-one on-both on) as standby. You have to just reroute the 0 volt wire from the mains to the plug socket, run the hot wire from the outlet and the 120v tap from the main to circuit 1 of the 3 way, disconnect the High Voltage AC Ct wire from the board, run it and a new wire soldered to that spot to the lugs of circuit 2. I Replaced the Output tube’s grid leak resistor R9 with a 500K pot with a 470K resistor across the sweeper and ground side of the pot (to protect the el84, if the pot goes) for a Master Volume. Provides a master Volume of sorts. It does affect overall output volume. You can dial up the old volume to full and get the max preamp distortion, and dial volume down. Stock, that gets you some crunch at lw volume. But, with the original volume pot, it also allows for mixing and changing amounts of preamp and output tube distortion for a lot of tone variance. Really like some of the different dirt tones you can get this way. Still, really need VVR mod, or attenuation to get the best of that. Or run loud Likely will add a VVR at some point. But for now, works fantastic with my Badcat Unleash. Moved the Pentode/triode switch to the back of the amp to make room for that MV. Cut the Europe leads from the mains transformer, at the transformer. They won't be used, and were parked onto an unused, and unconnected tabs on the board. They added a lot of noise to the amp. I also moved the othe transformer lines away from the board as best I could and hot glued to the chassis, to also reduce noise. I also re-hotglued Electrolytic caps I changed, and some axials I added that were soldered on only one leg, to reduce vibration effects. Went with the 'large cap mod' for the EL84 cathode bypass cap C7. Went to 1000uf. Did to keep the bias from drifting, block cross-over distortion (buzziness) and tighten up the bass after the other changes, and keep the low end fartiness away. Changed the Mid and Bass filter ,022uf caps to better quality Mallory 150 caps. Same for the coupling cap from the 2nd preamp stage to the output. Now on to the tone and gain related changes. First, lowered the V1B, or 2nd preamp stage's, cathode resistor from 1.5k carbon film, to a 680ohm metal film resistor. This biases the the V1B stage a little warmer, more ‘marshally’ on the clipping, and reduces noise with the metal film. Changed the V1A and V1B cathode bypass Caps C1 and C5 to 2u2 electrolytics, to cut some, and thus tighten up, bass, as it also boosts the lower end gain, This brings both more in line with typical marshall values, with a little more marshall mid boost as well. Changed R4 and R8, the two preamp plate resistors, to carbon composites to sweeten the tone a bit. Lot of debate out there on the benefits, if any. But some Gurus I respect, adhere to them sweetening tone when used in proper spots like plate resistors. Due to their high voltage coefficient of resistance, their resistance varies with the voltage across them. The effect of this is they distort, with pure 2nd order harmonics. In other words, they distort in a way our hearing likes. Don't really hear the distortion. What it sounds like though, is a vintage 'sweetness. But, have to use them in the right spot, as they bring higher drift and noise as well. Plate resistor is a perfect spot. I tried low noise metal filters in their (stock were carbon film). Tone was definitely more 'clinical'. I definitely like it better with carbon comps. I added some liquid shielding to the resistor wires to reduce their added noise a little. Not that it will do much, as most of the noise is from inside the resistor and how it's built. Lowered R5, the slope resistor in the tone stack to 33K. This put it in marshall Territory. Moved the mid cut/attenuation frequency up from 300hz to 550, and lessened the attenuation by 6 db. Basically added more lows, low mids and mids. Also an overall gain boost. Changed to lower noise metal film. Stock, was a mix of Fender and Marshall values in the stack. Also, lowered the Treble cap to 330p for two reasons. One was to take a little bit of the top end harshness/beaminess out of the amp. Also wanted to adjust the mid attenuation a db or 2, so that stock tone was JTM45ish, generally speaking. But I could still give a mid and gain boost with another mod and have a more Plexi setting. While I was at it, I replaced the ceramic with a silver Mica to get rid of graininess. So, the basic stock changes, made the tone stack go from factory (Green) to the yellow. Can see the boosted lows and mids, and overall increased gain. I also added a Bitmo Triple bypass. It has one position that is stock, middle which bypasses the tone stack for the most part, and replaces with a basic Princeton tweed like tone circuit, and a third that boosts the mids and adds a little more mid gain, at the expense of reducing the effect of the mid and treble pots. Tone stack on this amp really eats gain and volume. Ergo the two bypass modes. So, the end result gives the stock at a somewhat hot rodded JTM45 territory, the Bitmo mid boost adds to the other mods, to bring the tone into the Plexi area. And have the tweedish setting as well. Overall, the amp is extremely responsive. The overall tone has the harshness removed from the top end, smoothed out the distortion and is now very, very versatile. And that is just on the pentode setting. Amp sounds fantastic with multiple different classic rock dirt tones. Very happy with the tone, noise and performance. Not as happy with some of my water slide decals I created. Might redo those. Now the pics.