Instrument Resources

Although similar to 16s and 16Bs in appearance and size, the Marantz 14 and 15 amplifier is completely different. The 15 is basically a discrete differential amp design with current amplification, it has few components and is of extremely high quality. It has a transparent sound not found in most bipolar amps. In my opinion, it is one of the best little amps and one of my personal favorites. It uses a healthy power transformer and the heat sinks provide adequate cooling for three times its power. The third design was so successful, it continued in the model 18 and 19, of course without the light bulbs and had a few value changes. To the best of my knowledge, there are three different designs of the Marantz 15.
The first design uses series regulators for current limiting and no speaker protect relay. Using a speaker fuse or external relay circuit is recommended, in case this amp lets go. This will prevent further amplifier damage and protect the speakers.

The second design uses the same series regulation for over-current protection, but now incorporates a speaker protect relay. This relay needs attention on every 15, 18 and 19 that I have seen. There is a high silver content on the contacts with small surface area and low tension. They sulfate easily and should be cleaned on a regular basis. In addition to this, I have seen a few relays where the contact is not peened hard enough on the metal, and no matter how hard you clean it, it doesn’t help. I can rectify this situation with the original relay.

The third design eliminates the series regulation for current limiting. It uses a conventional protection method on an additional board. This third design also uses the speaker protect relay. The series regulators [TO-66s] on the heat sink are eliminated. The current limiting board is located behind the transformer. This board is secured by one screw. A few capacitors have been eliminated on this board for a few serial numbers midway through this design. Then these capacitors reappear on some of the later serial numbers.

The drawbacks are, (like every amp that has trade-offs) a poor relay in later designs, no relay in the early design. The lamps should have been soldered in. The first two designs should have had additional protection circuitry in case the lamps opened. The last design won't destroy the transistors when the lamps open, it will just burn one or two resistors.

This amp benefits when Q102 and Q103 are carefully selected and matched. Also to its benefit, but to a lesser degree, matching the output transistors, Q110 and Q113 helps. I like to keep the beta ranges on these transistors on the low side.

I have designed, redesigned, modified, and repaired audio equipment for over 50 years, and specialize in Marantz 7T, 14, 15, 16, 16M, 16B, 18, and 19. Shown below are a few of the Marantz 15s (3 versions), 16s, and 16Bs that have been restored and/or modified. Also shown is a 15 and 16, specifically used to test new types of components. These are a few from my collection.