Ready to hear your headphones erupt in a prismatic spray of golden tones? The MG Head OTL is your ticket. It sounds amazing, looks cool, and best of all is quite affordable. At $350 it has few, if any, peers. For best performance, potential owners of the MG Head OTL should keep the following two guidelines in mind: (1) Use high impedance headphones and (2) Replace the tubes. Suitable high impedance headphones include the popular Sennheiser HD580 and HD600 headphones at 300ohms each. As for upgrading the tubes... it's a snap if you know what to look for. 'Tube rolling' as simple as changing a lightbulb. Just as different lightbulbs can portray romantic, serene, or studious moods within a room, so will different tubes affect the overall sound of the MG Head OTL. To make tube rolling work its magic for you, simply collect a few tubes, swap them out, and keep the ones that sound best. The results can be dramatic! ROUND ONE - FIRST IMPRESSIONS Two 1/4-inch headphone jacks are located on the front panel of the MG Head OTL: One marked HEADPHONE and the other OTL. Only one jack can be used at a time. The HEADPHONE jack amplifies the signal using the internal transformer, while the OTL jack (Output Transformer-Less) bypasses it for an "all  tube sound". Two amps in one! ROUND TWO - TUBE ROLLING THE MG HEAD OTL The MG Head OTL uses three tubes: two tall EL84 power tubes and a smaller 12ax7 signal tube. I swapped out the Sovtek brand EL84's first, using a pair manufactured by JJ Electronic and another pair by Ei Yugo. The JJ's were first. The change was subtle but noticeable. A layer of thinness was lifted from the music, leaving a slightly more full bodied presentation in its place. The top frequencies also gained a little sizzle. Drumsticks snapped with a pleasant *thwack*. I was pleased. Next, the JJ's were swapped for the Ei Yugo EL84's. The improvement over the stock Sovtek tubes was similar, but the emphasis favored the lower octaves this time. More bass, less sparkle. Both pairs of replacement tubes delivered better sound than the stock EL84's. I decided to keep the JJ Electronic EL84's and send the Ei Yugo's off to eBay. The Ei's sacrificed too much high frequency sparkle for my tastes. ROUND THREE - ROLLING THE CENTER TUBE This is where tube rolling the MG Head OTL pays off big time. The center tube has the greatest effect upon the overall sound. This is where the magic happens. My MG Head OTL was supplied with a JJ Electronic ECC83 installed in the center socket. Although I am a fan of JJ Electronic's tubes, their ECC83 isn't one of them. It's a fuzzy, uninspiring tube that ranks near the bottom of the heap. There's nowhere to go but up. WAY up. Out went the JJ, and in went a Svetlana 12ax7. Big difference. The midrange and bass frequencies were deepened to thunderous levels. It was overwhelming. The highs also lost a little sparkle. Cymbals sounded like they were being struck with drumsticks made of felt. No thanks. Neither of these tubes are remarkable. The JJ is uninspiring, and the Svetlana is skewed too heavily towards the bass frequencies. After reading "Joe's Tube Lore", I ordered a batch of 5751 tubes. They are a low noise, compatible version of the 12ax7. ROUND FOUR - SECRET AGENT 5751 AT YOUR SERVICE My first shipment of four 5751's arrived. Each tube was manufactured by a different company: G.E., Raytheon, Arcturus, and RCA. I tried the G.E. 5751 first, swapping out the old Svetlana in the process. The volume knob had to be ratcheted up a few steps due to the lower gain of the 5751. This was a good thing, because there was now more "play" in the volume knob, leaving room for making finer volume adjustments. The result? Everything improved DRAMATICALLY. All frequencies were rendered with an entirely new level of clarity. Everything was better... lows, highs, clarity, details, you name it! This was the breakthrough I was looking for. Bass was deep and taut, the midrange exuded lush tube goodness, and the highs were clear and exciting. Score! Compared with the previous 12ax7 tubes, the 5751 is in a different league of performance altogether. Physically, the G.E. 5751 was marked JG-5751 and had black plates with 3 mica spacers inside. The RCA 5751 was next. It presented a mellower character than the G.E. Cymbals and high notes had less attack than before, but was still acceptable. "Warm" and "lush" are perfect adjectives to describe this tube. Classical music sounded best with it. The RCA 5751 had two black plates and two mica spacers inside. The writing was rubbed off, so I couldn't tell if it was a Command series tube or not. Remember to handle them gently to avoid rubbing off the label. Next came the Arcturus 5751. I snagged it from eBay and haven't seen this wacky brand for sale anywhere else on the internet. No matter, it was an unimpressive tube. The Arcturus was slightly better than the original JJ ECC83, but that's about it. Nothing to write home about. The final 5751 was the Raytheon which proved to be the most spectacular by far. Everything the G.E. and RCA 5751's could do, this one did it better. Top end sizzle was crisp, midrange vocals were emotional and realistic, and bass notes arrived in just the right amount of tight, accurate slam. A righteous tube! The Raytheon 5751 has two black plates, two mica spacers, and a getter at the top that looks like a miniature fan. If you see one for sale, grab it! ROUND FIVE - ODDBALL FROM EBAY I ordered another 12ax7 variant called the 7025. It was an ITT brand tube, which was probably manufactured by another company and re-labeled as such. It had the typical appearance: two grey plates, two mica spacers, and a round getter at the top. Surprisingly, the ITT 7025 is a very good tube. It is respectably similar to the incredible Raytheon, but lacks that last ounce of finesse and tonal balance. If you can manage to find this oddball, pick it up! This one was new and only cost me $4... well worth it. ROUND SIX - THE ELITE 5751's At the top of the recommendations list in "Joe's Tube Lore" is the Sylvania 5751. It is a triple-mica, black plated beast that is supposedly the creme de la creme of 5751's. I netted one from an eBay auction along with another recommended tube, the Tung-Sol 5751. Was Joe correct? Absolutely. The Sylvania is the best 5751 I own. It is marked JHS 5751WA with yellow lettering. I have also seen other ones with gold lettering. This tube is similar but slightly superior to the Raytheon, adding a further touch of midrange magic to the mix. Find it and know the joy. As for the Tung-Sol 5751, it has a character all its own. With its large twin internal grey plates, it resembles no other 5751 tube I have ever seen. I consider it the big brother of the RCA... sounding similarly "lush", "warm", and occasionally "syrupy" but to an even greater degree. It has that traditional "tube sound" in spades. The Tung-Sol would be the ideal choice for an evening with Pink Floyd... launching your brain directly into outer space. WRAPUP Tube rolling the MG Head OTL was a time consuming process but very much worth the effort. It is amazing how different tubes can transform this affordable little amp into a performance monster. Here's what I recommend of the ones tested: SUPERIOR - Sylvania blackplate 3-mica 5751 (marked JHS or CAA), Sylvania Gold Brand 5751 (look for the gold pins!) according to Joe's Tube Lore, and the Raytheon blackplate 5751. EXCELLENT - ITT 7025 and Tung-Sol 5751 (has unique long grey plates). Choose the ITT for all-around performance, or the Tung Sol for a lush experience. VERY GOOD - G.E. blackplate 3-mica 5751, and RCA blackplate 5751 (many different types of RCA's out there... try a few different ones for yourself). All are quite nice and give up little to the above. eBay is a good source of NOS (new old stock) and used tubes. A Yahoo search may also turn up a handful of audio equipment dealers who may have some vintage tubes for sale. You should also check with your local TV repairman. He might have some forgotten gems sitting around on the shelf. Happy hunting! Feel free to ask any further questions at one of my favorite hangouts... Head-Fi.com!