Blackheart BH-15 mods

This page covers the mods I’ve made to my Blackheart BH-15 valve amp.  Although as standard it’s an excellent, single channel all valve amp, there were mods available for it, and in some respects it was designed to be modified!

Here’s the blurb about it from the Blackheart website :

Designed and prototyped in a one car garage in Austin, Texas, by non other than amp savant, Pyotr Belov, the Handsome Devil evokes classic tube tones more than reminiscent of the great American and British, plug and play workhorses that laid the foundation for Rock and Roll guitar tone starting in the ’60s. Just like it’s predecessor and little brother, the Little Giant 5, the BHE Handsome Devil is overbuilt to last with features and components you’d expect on a hand built, much more expensive piece of gear. Both the head and combo feature dual power modes allowing the Gods of Rock to dial in responsiveness and headroom in either 15W or 7W output. Separate Master and Level controls put both awesome power and responsibility in the unwashed hands of mankind. 3 Bands of well-tuned EQ make for nearly infinite voicing. From big fat overdrive to plucky, just-about-to-squeal if you hit me a little harder grease, the Handsome Devil covers classic tube tone with as few knob turns as possible through a well thought out set of features in a tough as a tank package.

As expected, you get the simple elegance and robust component specs that mark BHE’s designs. From 1W, carbon-film resistors in the signal path to beefy, double sided pcb with 2 oz traces, 16 gauge, precision folded and welded chassis and mutli-ply, classically joined cabinetry, Blackheart is as serious about quality as they are about tone.

Available in a surprisingly compact head (BH15H) or single (but looking) 12″ combo featuring the specially designed 1216B Eminence speaker developed by Blackheart Engineering and Eminence Speakers.

Hear the B15 now for yourself!

Download the Owner’s Manual in PDF format here.

 

SPECS:

• » 15 Watts, Push-Pull, Class A
• » Outputs: 1 x 16 ohm jack, 2 x 8 ohm jacks, 2 x 4 ohm jacks
• » Preamps Tubes: 2 x 12AX7
• » Power Tubes: 2 x EL84
• » Solid State Rectifier with tap for future mods
• » Drive, Level, Treble, Mid, Bass and Presence controls
• » Pentode (15 Watts)/Triode (7 Watts) Switch
• » DC Power to filaments for super quiet operation
• » 15 ply (18mm) thick-void free plywood construction
• » 12″ Blackheart Model 1216A Speaker by Eminence with American Voicing, optimized for open back cabinet

 

It’s a 15W/7W combo which is built like the proverbial brick building.  Compared to the Marshall Class 5 which I had before it, the Blackheart is made from far better materials.  I’d confidently expect this combo to survive almost anything up to a nuclear blast.  It’s heavy, the steelwork is excellent and the PCB is very solid.

The mods I’ve made are:

1. Adding the Bitmo voicing mod  (gives it 3 voicing options)
2. Adding a valve rectifier  (thus giving it the choice of using sold state or valve rectification)
3. Adding a Carling Off-Standy-On mains switch.

 

1.  The Bitmo Dapper Devil vocing mod.

BH15 Handsome Devil – Dapper Devil Switch

This gives it 3 voicings – “Stock”, “Tweed” and “Over the Top Boost”.   (I’ve labeled the switch as STO)

Tremendously flexible and great sounding amp. Lots of clean headroom, crunch and overdrive, and a master volume control. Each setting reconfigures the tone stack and gain. Upgrades all coupling and tone capacitors.  You can  hear more about this modification here – where Bitmo Bruce demos his mods.

In fitting this mod, although the instructions suggested that you should cut the legs of the components being replaced  (capacitors mainly) and then solder the replacement higher quality components to the stubs of the legs this didn’t seem to me to be the best thing to do with them.  Instead I totally removed the components and soldered the replacements directly to the PCB, just as is done in the factory.  Although it was a slightly longer process, the payoff for me is that they’re installed properly with no chance of ever breaking down.

 

2. The Alnicomagnet Dual Rectifier Mod
I fancied using an EZ81 valve rectifier in this amp. Just to let my ears hear the differences between valve rectification and solid-state rectification.

The easiest way to do this was to install the mod kit supplied on ebay by Alnicomagnet.   The BH15-112 both use a mains (power) transformer which has a separate unused 6 volt secondary winding suitable for an EZ81 6.3 volt valve rectifier.  In fact, it seems to have been designed to permit after market modifications.

The beauty of a valve rectifier is the absence of any harsh “switching noise” that can sometimes plague solid state diodes. Also, it has an inherent “soft start” which is much kinder on the preamp and output valves. You can probably get away with not fitting a Standby Switch, IF you fit and use the valve rectifier at all times. (NOTE – I fitted an OFF-STANDBY-ON switch anyway…….)

Probably the major reason though for fitting a valve rectifier is to induce “vintage sag” or soft natural valve “compression” to the sound when playing loudly.

Unlike in a true Class A amp where the current flowing through the output valve(s) does not increase (much) with increase in output power, in Class AB the current flow does increase substantially with increase in output power. Solid state rectification is a low impedance power supply, whereas valve rectification is a high impedance power supply. So an increase in output power and corresponding increase in current draw will drop more voltage across the valve rectifier, thus inducing the phenomenen more commonly known as “sag”, or soft natural valve “compression”.

I have made it switchable with the stock solid state diodes, as a “failsafe” should the valve rectifier fail. Centre position is “OFF” and can be used as a “standby” position, enabling both the output and preamp valves to warm up fully before selecting either rectifier to power the HT circuit.

 

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