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View Full Version : BH5H Bitmo triple bypass mod installed


The Boathouse
09/11/08, 07:13 AM
Success!

I installed the mod about 2 weeks ago. My favorite of the three selections on the switch is the middle, which gives me an absolutely absurd level of clean headroom. The bottom selection adds a hair more gain, and the top selection adds a fairly large amount with a sort of dark sound to it. I've found that the mod allows the EQ to function more sensitively and reasonably. I had qualms with the EQ for a time on the Blackheart Bh5h, but had grown to adjust to it. The treble, I felt, reacted harshly, and often seemed too cutting. The mod mellowed the highs out, making them more bell-like and less volatile in the mix. The bass has been evened out a bit, which could at times get boomy at higher levels.

Anyway, onto my in-depth analaysis of the middle selection...

The clean headroom on 3 watts rides fully to the end of the volume knob when using my middle pickups and neck pickups on my Gibson Nighthawk. I suspect Strats and Teles would react similarly in similar positions. The two bottom selections break up a bit before the end of the knob, though only slightly, and not nearly as much as I had encountered before I installed the mod. I consider this a huge step forward for the amp, as I have often felt that there was too little clean headroom, and that the gain gradually grew overpowering, with the volume knob seeming to function less and less, with it translating into more of a "gain" knob, instead of growing louder, only breaking up more. I understand that 5 and 3 watts are limited, but I would have preferred volume to extend farther around the knob. With this mod, I have that.

The 5 watt mode breaks up before the end of the dial. This is fine and expected, as it is a higher power channel, and preceding the mod, would breakup earlier than 3 as well, and get considerably ballsier as it broke up. The 3 watt sounds significantly more compressed, in that glorious, tube amp fashion. Rolling back the volume on my guitar on the 5 watt setting seems to chill the breakup a bit, letting me dial in cleans at higher volumes.

This mod, accompanied by a JAN-Phiips 12-AT7 in place of the 12-AX7 generally found in the preamp, has lowered the gain, sweetened the tone in all spectrums (though not previously mentioned, the mids have mellowed as well, making them less abrasive and warmer), and given me SUBSTANTIALLY more clean headroom. If you're concerned about dropping $150+ on the point-to-point turret board mod, or just too poor at the moment, this mod could easily hold you over until you can get the cash together for that one, which was my plan.

Instructions: Clear and concise - 8/10
Parts provided: 10/10
Functionality: 8/10 (I do not care for the top setting, but that's more personal preference than a mod problem)
Value: Now knowing what the parts list is for the mod, without the instructions, it would be unfair to pay such a pricetag on the mod, but with the fellow's instructions, I can deal - 7/10
Overall: 8/10 - Recommended!

patrickhowell
09/11/08, 08:50 AM
+1 on the 12AT7, that's the tube I have in my Valve Junior. I'd really like to get ahold of a 5751 and try that out, too.

The middle switch, the one that gives you way more cleans, is that Negative Feedback? (Signal from the output transformer re-introduced before the power amp)

Also, the "volume" on your amp is the same thing that is labelled "gain" on most amps. It's a variable resistor between the two gain stages in your preamp tube. Adding a "master volume" is fairly simple, but also mostly useless in single-ended amps. If you want more clean headroom after installing a negative feedback switch, you really just need a more powerful amp.

The Boathouse
09/11/08, 08:59 PM
Yea, it's the negative feedback switch, I'm fairly sure. I knew about how my volume is effectively just a gain knob, and that I just really need a bigger amp, but I've been trying to squeeze as much out of my dear blackheart as possible before making that jump. I love the clean tone it does get, so I've been trying to sort of make it a Hanukkah lamp of cleans, lasting longer than logical sense allows.

patrickhowell
09/11/08, 09:44 PM
Yea, it's the negative feedback switch, I'm fairly sure. I knew about how my volume is effectively just a gain knob, and that I just really need a bigger amp, but I've been trying to squeeze as much out of my dear blackheart as possible before making that jump. I love the clean tone it does get, so I've been trying to sort of make it a Hanukkah lamp of cleans, lasting longer than logical sense allows.

Haha, you could try going to Eurotubes.com and ordering a new EL84. They measure each tube that they sell and they can sell you one specifically for more clean headroom. Also, you could try playing through a more efficient speaker setup. What speaker(s) are you playing it through now? If none of that works, you could try doing an octal tube mod and running an EL34, 6L6, or any other "big tube" in your power amp. I'm not really finding much info on that for the Blackheart though... Maybe upgrading the Output Transformer would give you a little more clean headroom too.

The Boathouse
09/12/08, 10:10 AM
I was thinking of one of those specially measured power tubes, can't really hurt. I've read a bit on the OT, and most people have said it "isn't worth replacing," as it's apparently fairly good. I figure I'll end up changing it out for a new one within the next 6 months anyway, just to see what can be done. The octal mod is enticing, so I'll post if I end up throwing that in there.

patrickhowell
09/12/08, 12:14 PM
I was thinking of one of those specially measured power tubes, can't really hurt. I've read a bit on the OT, and most people have said it "isn't worth replacing," as it's apparently fairly good. I figure I'll end up changing it out for a new one within the next 6 months anyway, just to see what can be done. The octal mod is enticing, so I'll post if I end up throwing that in there.

The OT might be fine, but you might be getting some OT saturation and losing some of your cleans at higher volumes. Also, you could try a conjunctive filter or presence control to smooth out some of the harshness you get from a single-ended class A amp. Either of them would be really simple. The CF is just a capacitor and resistor across the primary side of the OT, and the presence just takes your NFB and bleeds some of the highs to the ground. And you could clean up a little bit more with a LO-Z input too. The BH comes with a HI-Z input, and the VJ comes with a LO-Z input. I have both on my amp (Like the #1 and #2 inputs on classic Fender, Marshall amps). Here's a schematic for an SPDT switch: http://www.sewatt.com/files/sewatt/impedance%20switching%20-%20SPDT.GIF

The Boathouse
09/12/08, 05:51 PM
Thanks man!

Pythagoras
12/27/09, 07:31 PM
One way to increase gain with the BH5H is to get one of the Bitmo 10-Uattor units which you can connect to the speaker output. They have a line output jack (with a level pot) which you can chain to another amp. I run the BH5H the the 10-Uattor into a 100watt solid state 2x12 Gibson/LabSeries L5 amp if I want a lot of volume with the tone coming from the Blackheart. I'm rebuilding an old Fender tube amp that has six 6L6's in the output section to get a high power all tube rig (been sitting in my garage for 15 years with bad caps), that particular amp has no usable overdrive so the Class A BH5H supplies the tone and the other amp drives the speakers. You can hook up the BH to a 12" speaker or something so it has a dynamic load to push against at the same time as the signal is chaining to a bigger amp. Next decision the P2P turretboard or the Btmo triple, this thread was helpful info, thanks.