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Ed. note: The following is excerpted from the Hoffman Amplifiers forum. For the originals, please visit the following links: http://www.el34world.com/Forum/index.php?topic=4360.0 and http://fydamps.com/photo4_1.html Originator info: Dan Lurie / Tube Amp Repair (802) 863-9525 South Burlington, Vermont
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Blackheart conversion
Mojo kit & Mercury Magnetics Kits
I got the Mercury Magnetics (www.MercuryMagnetics.com) XLG Upgrade Kit in for the amp. The kit is really designed to modify a stock amp with the PC board [ed. note: This Blackheart was built around a Mojo point-to-point mod kit www.MojoMusicalSupply.com]. Besides the power transformer, choke and output transformer, it has a few parts to modify the board slightly.
One interesting note: The Mercury power transformer does not have a winding for the tube rectifier. I spoke to Mercury and they explained it just had too much flab on the low end (I understood and do agree with that).
The kit comes with a CD
that has all the instructions to do the install and
mods. It provides schematics and photos of each step.
Very precise. Of course, me being an experienced tech, I
don't need no stinkin' instructions, so I threw out the CD
(kidding!).
Next... The output transformer swap and
comparison.
OT swap only
Last night we did an
A/B blind swap test with the original Blackheart
output and the
Mercury Magnetics
output. The Mercury Magnetics OT won! The tone of the amp got fuller and there seems to be more
definition or note separation. I am impressed. Can't wait to do the complete conversion and add the
power transformer and
choke.
How much was the
Mercury XLG Upgrade
Kit ?
Every penny. Wow! The tone of this amp is
chimmy and full bodied. It's got tons of tone. Possibly
one of the best sounding amps I've played. I'm a believer! The
tone controls provide a full array of tones. When cranked the
amp sings.
Check out the pictures (click
on either for a larger view)....
How much does it come down to (money wise) to do such a project?
I did double work on this one. I converted to the Mojo P.T.P. board and buttoned everything up. Then I disassembled EVERYTHING and installed Mercury's XLG Upgrade Kit. Probably wasted a good 1-1/2 hours with the extra steps. Many hours to complete.
Amp head: $250 (check the web it will go down)
Mojo board: $ 90 unloaded ($150 loaded)
Mercury XLG Upgrade Kit: $270
D.I.Y.: $610.00 (worth it)
It is truly a boutique amp now. I played
it all night. My wife came in and didn't tell me to turn
it down but did tell me it sounded really nice (she
never did that before!!).
One more comment: I've been
using my EVM-12L loaded shop speaker during the entire
project. When we hooked up the stock Blackheart speaker
cab we were extremely disappointed. That stock cab has
NO tone.
Interesting report from the local music store: The owner of the amp brought it to the music store (I was not present). The word is the amp is one of the best sounding amp they ever heard and played. -- NO KIDDING!!!
It that cool, or what?
I setup a page on my website: Blackheart amp conversion -- http://fydamps.com/photo4_1.html
Great project!
For more information, assistance, quotes
or inquiries:

9167 Independence Ave. • Chatsworth,
CA 91311 • FAX (818) 998-7835
Info@MercuryMagnetics.com
•
www.MercuryMagnetics.com
PRICE LIST / CATALOG
(818) 998-7791