Caring for Your Marantz 10B FM Tuner
by Robert H. Levi

You probably noticed I love writing about the famed Marantz FM tuner, primarily because, as vintage gear goes, it just does not let you down. When it misbehaves, it is easily repaired and then sounds as good as ever. I recommend Brooks Berdan, LTD in Monrovia, CA, for great repair service at real world prices. What's new about all this, you ask? I just received my tuner back from its annual service checkup, and it has taken a sonic leap surpassing its previously excellent sound quality. If you own one of these beauties, read on.

I began having trouble with adequate right to left separation and an occasional switch to mono sound even though it was on a stereo channel. My interconnects were also coming disconnected from the old tin vertical RCAs on the chassis. I had no idea how repairing these two problems would transform the 10B into a tuner far superior to what I had though quite fine and world class.

Once returned and warmed up, I compared it to my Day Sequerra Reference and Magnum Dynalab 108 Reference tuners. It magnificently trumped both for definition and charm. There was a remarkable increase in clarity with an entire veil of grunge and overly ripe tube warmth completely eliminated. The exquisite definition and organic sound was dramatically enhanced, depth and stereo separation was as good as my best CD sources, background was dead black quiet, and I felt quite stunned by the overall results. When I had 18 tubes replaced last year, I did not get this kind of improvement. This was new tuner sound…it was again 1967, and I had just fired up my new Marantz FM tuner! What gives?

Here's what I did. The very smart repair specialist checked it out and announced that my opto couplers needed replacing with new specially built units. In addition, the old tin RCAs screw into the chassis and can be replaced, without auguring holes already there, with much better gold Tiffany connectors. You would have to drill the chassis for Cardas RCAs and there was no way I would do that. The Tiffany connectors screw right into place [I saved the old ones for future whatever.]

We went on EBay and found a seller who builds opto couplers for a hobby for 10Bs. I guess there's someone out there that does just about everything. The old couplers and most NOS units crack from age and leak light whether used or not. I'm told they are not difficult to build from scratch and they only cost me $150. This is very advanced engineering for 1967, but easy as pie today. Anyway, the three new, well-made opto couplers were installed along with the Tiffany connectors. All other parameters were adjusted and all tubes checked, but none needed replacement.

The results: flabbergasting! The precise, highly defined, gorgeous definition is new. It sounds new! I don't know how much of the dramatic improvement is the connectors and how much is the opto couplers, but my technician suggested it was mostly the opto couplers that I was hearing. I am mightily impressed. So much so, that I recommend you replace your 40+ year old opto couplers and the tin RCAs, whether you need it or not, as soon as you can! Eighteen new tubes made less of a difference than the couplers and the connectors!

With these replaced and all other things working properly, you, too, will have the same jaw dropping experience I just had. I always wondered what the Marantz sounded like brand new. Here's your chance. You don't even need a time machine. Just a hand full of parts will do. Happy listening and continue to enjoy free FM!