Saturday, July 6, 2013

Bogner Alchemist 2x12 Service Review












This service review is likely to be a little partial because I liked this amp so much and I was so impressed by the internal details I went out and got myself one by horse trading with a guy from over in Nebraska who needed something different himself.

The Bogner Alchemist is a 40w, 2 channel amp with digital reverb and delay onboard. It comes in three varieties-a 1x12 combo, a head and cabinet, and the one here which is a 2x12 setup. The speaker choice is at first a little odd, being a Vintage 30 Celestion below and a Greenback on the top. Reinhold Bogner, the witty proprietor of the Bogner empire says that it's for a reason. If you want to mic one tone, pick the speaker you want to mic. They're slightly different.

The amp's made in China in the Line 6 factory. Reinhold Bogner says that this allowed him to build something to his specifications, keep the price manageable and take advantage of the Line 6 broad based distribution and service network. He also says that a lot of the components in the Alchemist were brought in to China because some things were not locally available. The cabinet is made of birch plywood-no MDF here. Opening it up, capacitors from Sprague, Wima, Mallory, Nichicon, Xicon and Nippon Chemicon abound. The iron came from the Chuang Meei works in Taiwan and the transformers are well finished and beefy.

The chassis is constructed of .068 sheet steel, spot welded at the corners and powder coated. The circuit boards have nice wide traces and are well supported-no flexing when you push a tube into its socket. Another good touch is 4 plastic chassis screw guides that pop into the chassis and guide your attachment screws down into their mating holes.

And, except for the effects board there are NO surface mount devices like you find all over a Blackstar. That brings us to the subject of maintainability, and the complete build manual for the Alchemist can be downloaded here. The owner's manual is readily available too.

http://elektrotanya.com/line_6_alchemist_sm.pdf/download.html

That brings us to the power supply. The filtration is good, and all the power supply goodies are mounted on a separate circuit board, In fact there are six boards, each with their own function, connected by ribbon cables and hard wires. One thing's for sure-there is no shortage of fuses. There are the externals-a 2.5a slow blow 5x20 in the IEC socket, and an 0.5 a slow blow in the fuse holder. But it doesn't end there.  On the power supply board there are two more-an 8 amp 5x20 slow blow for the 6.3v filament circuit and a 1.0a slow blow for the B+ supply.

If you own an Alchemist make sure you order some 8a slow blow 5x20 fuses because they're not easy to find. Mouser Electronics has them.

Other nice touches include a shielded input with ferrite rings for noise suppression.

The glassware that came with the amp was a little odd. There were 4 Mesa 12AX7s and a Ruby marked 12AX7 which was nearly defunct. Out they went, to be replaced with 2 new RCAs and 3 BEL 12AX7s. After installation one RCA and one BEL were found to be a bit noisy so I subbed in a pair of 6681s.

I am running pretty short of my last ditch preamp tamer Philips 6681s I got a while ago, so I looked around and found a guy selling Penta Labs 6681s. The original 6681s were a premium mobile rated tube, very stable and quiet and just the ticket to tame an overly energetic preamp. These were something of a product test to see if they were anywhere near as good as the Philips items. So far, so good but keep your shirt on for a while.

The power tubes are Ruby 6L6GCMSTRs, and I decided to keep them because that's what I sell my customers and they've performed well for me. Another nice touch is that the power tube bias is individually adjustable for each tube via a pair of Bourns multi turn pots. No more worrying about mismatched tubes. I was able to dial the power tubes in to within .1 ma, which is pretty damn good.  I removed the cage around the power tubes, it's not needed and is probably there to satisfy safety regulator types. There is also a small trimmer on the power supply board marked R3 I think, no idea what it's for so I left it alone.

There are three qualities any guitar amp or bass amp must have to make it in the big wide world-it must be reliable and sound good or else it's a piece of crap, as Reinhold Bogner says, and I would add that it must be serviceable out in the world and follow the Donald Douglas rule of "How will it do in Peoria?". I have seen some commentary on various forums about the foot pedal plug being a dodgy proposition but I haven't tried mine and don't intend to bother with it. A number of people have talked about the Alchemist DOA syndrome which I suspect is traceable to the 6.3v 8a fuse-that was what was wrong with the one I worked on. Time will, of course tell what the reliability ends up being but for now it looks OK.

For now, I'd give this amp a preliminary thumbs up. The price is right and they aren't making them anymore, and it is a lot better built than a comparable Deville or Blackstar as well as sounding more smooth and well behaved in my biased opinion.

10 comments:

  1. Is 35 MA the right Bias setting for the Bogner Alchemist ?

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  2. Depending on your plate voltage and the method by which you measure bias current, that would be within the serviceable range. As you can see from the picture mine is running at 40.3 to 40.4 ma. I use the cathode current measuring procedure with a bias probe I built from parts from Hoffman Amps.

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  3. Hi Robert..

    Thanks for the pics and info. I live in Australia,.Mains Power here is 240v. I bought my Alchemist from the US and Wondering if the PT is tap-able from 120v to 240?, or would I need to get a new PT for 240v??..

    Many thanks..
    Jess

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  4. I would download the build manual that I provided a link to and then review it with your amp tech. If you have to have a different transformer it might be easier to use a step down transformer.

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  5. Hi Robert,

    Thanks for the article - can you tell me where on the board to measure the bias current?

    Thanks,

    Neil Glover

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  6. I use a bias adapter. I got the kits for them from Hoffman and built them. You can buy them ready made from any number of sources. The Weber Bias Rite is a good unit. There may also be a test point on the circuit board but to tell the truth I never looked for it.

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    Replies
    1. Many thanks for the advice, Robert. I'll give it a go!

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  7. It wasn't difficult to do, and you can get the power tubes nicely matched.

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  8. Is this amp still working well for you? Considering one but concerned about reliability.

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  9. I parted company with this amp a few months ago so I don't know how it's doing although it never gave me any trouble. I would say that in light of what you've mentioned I would have an amp mechanic give it a very careful going over before money changes hands.

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