I just got my David Allen modded SF head back last Friday. I sent it out the previous Friday so the turnaround time is amazing. It cost me $330 for the basic mod, mid boost on the normal channel, new filter caps, 2 TAD 6l6s, a 12at7, and shipping. He also did a few extra things to clean up the amp free of charge. The work looks first rate and is done with total respect for the vintage aspect of the amp (he left all the blue mallory caps intact and all mods are reversible). OK so what you really want to know is how does it sound?. Keeping in mind that I'm in the honeymoon phase and I haven't gigged it yet I would conservatively say that the Bass channel is...FANTASTIC! With the volume on 7 the thing growls like an old Marshall. In fact David told me that his circuit actually has MORE gain than an original plexi. It easily cops AC/DC gain and tones from humbuckers and a boost or OD pedal can put it into EVH land. Id love to a/b this amp with the Fender Tweed Bassman or Marshall JTM-45 reissues. I have a feeling that it would easily hold its own. Both settings (tweed/plexi) are useful with the Tweed setting having a fuller bass and slightly more gain and the plexi having a more punchy, focused midrange tone. I like the tweed sound at lower volumes and the plexi setting when the amp is cranked (although the extra bass in tweed mode never really gets flabby like a fender can). The normal channel is a clone of the stock AA864 BF bassman normal channel. Its got the classic punchy attack, scooped midrange and chimey treble that we all know and love. The only thing I dont like about it is that it seems VERY bass heavy (I have the bass on 1). I may modify the tone stack on this channel to reduce the low-end and have been in contact with David about this. The mid boost is a great feature that replaces the absolutely useless (IMO) bright switch. It increases the gain slightly, thickens the tone and cuts treble. All of this works wonders with the bridge pickup on my Tele and Strat although it can sound a bit dull on other pickup positions. All-in-all the amp now has a new lease on life. It sounds great, is way more versatile, and will now last another 30 years with only basic maintenance.