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Positive Feedback ISSUE 22
november/december 2005


Marantz 10B FM Tuner Compared to Magnum Dynalab MD 108: Tube Rolled!
by Robert H. Levi


You thought you had heard the last word from me, but no! The 108 will chase a 10B down the block and back again, and only if, you tube roll. Here’s the skinny.

I tried the Sovtek 12AX7 WXT, Mullard 12AX7, the Telefunken 12AX7, RCA Blackplate 12AX7, and the GE 5751 1970s production. The order in which I preferred these is as follows:

1. GE
2. RCA
3. Mullard
4. Telefunken
5. Sovtek

Surprised? The problem with the exotic Euro tubes is a tendency to stridency in the circuit. The performance of the 108 was just not involving with these $100 NOS beauties in the circuit. The Sovtek, as supplied by MD, was just as edgy and even less textured than all the others. Fully warmed up, the Sovteks became useable, but that was about it. The RCA was very close to the GEs though they were a bit hard sounding in this circuit. Once again, the magic is one uses the 5751 variant, which has a bit lower output and because of that, is much more complimentary. Perhaps any 5751 variant would be excellent, though the GE is killer. I could find no 12AX7 that was competitive, and I had no other 5751s to try …sorry.

The good news is the GEs are the cheapest tubes around at about $25 each for NOS low noise. They are used by many manufacturers, so you better stock up now while they are fairly inexpensive! Compared to the stock Marantz 10B tweaked to perfection, the 108 has superior bass slam and a bit more sparkle and snap. Overall definition is very similar. The Marantz is more textured in the mids with a bit more depth. The 108 is faster and slightly brighter, but similarly smooth and realistic. Bottom line: the Marantz 10B sounds like great phono cartridge, the 108 like great CD player. The Marantz exudes warmth and textural layering while the 108 suggests these virtues and adds more of  a "stage forward" definition. I surfed back and forth and enjoyed both tuners immensely. It’s hard to communicate my joy of the 108 with the GEs on board. What wonderful fun!

Summary of Tuners Compared in order of preference:

1. Marantz 10B Stock but perfectly aligned and retubed
2. MD 108 with NOS GE 5751s and using balanced outputs
3. Day Sequerra Reference Tuner updated in 1999 using balanced outputs
4. Mac MR 78 tweaked by Audio Classics

The 108 nearly equaled the overall performance of the 10B in most respects, but clearly outperformed the Day Sequerra—two tubes are better than no tubes at all. The Sequerra was very clear and smooth, but obviously less textured and warm than the 108. I missed that texturing from the moment the Sequerra was in the circuit. The bass was the only area equaled by the Sequerra when compared aganist the 108, but the 108 was clearly superior in all other ways!

The Mac is not in the same league as the other three tuners. Its sound was colder and less refined. I just don’t get it and am very disappointed. It sounds like it is; an older transistor design. It was not very musical or involving and decidedly a step or two behind current quality solid state designs on the market—at less money.

Until or if I acquire some different 5751s to try, that’s all for now. The GE 5751 is a bargain and MD should supply them in all 108s! Of course, with 19 tubes, the 10B is ripe for tube rolling, too. Not!

The Marantz 10B FM Tuner and the Magnum Dynalab MD-108 Reference Tuner: Forty Years of Progress, Sort Of!


Final Notes - The Marantz 10B FM Tuner and the Magnum Dynalab MD-108 Reference Tuners