1978 Music Man 115-RP

The Music Man instrument comapny was started in the 1970’s by Leo Fender after he sold Fender to CBS in 1968. He was head of the company in every way except on paper as he signed a multi-year Non-Compete deal with CBS. Leo Fender and team designed these amps to be cutting edge and to continue his pursuit of the cleanest and highest-volume/highest-wattage amplifiers possible. These amps can sound a lot like Fenders but the main differences are: They are made with vintage style PCB’s and some hand-wiring, they are hybrid amps that use all analog solid-state preamps and effects circuits, the power amps use 6CA7 power tubes (later models use 6L6GC’s) with a mix of Transistor cathode bias and fixed biasing on the grids, and they use extremely high plate voltages (700+ VDC!!) on the power tubes resulting in even more pristine clean tones that are suitable for guitar, lap/pedal steel, and bass. These are some of the only hybrid amps I like - The reason being, that with a solid-state preamp and tube output section the all important Output Transformer is kept which is one of the biggest reasons tube amps sound good for guitar/bass instrument usage. Almost all modern Hybrid amps do the opposite - they use a tube preamp section with a solid-state output section. Companies switched to this design not because of tone or reliability, but simply because of the huge cost savings in getting rid of the OT and power tube/high voltage requirements. This amplifier also sports something even more unusual - a completely analog Phaser effect built right into the amp. It sounds great and has a design that is very similar to the MXR Phase 100. This and the Spring Reverb make this amp something special. I think they are currently very under-valued in the vintage market - both in tone and price level.

The amp came in working but un-played in 30 years and needed a complete restoration. All filter/bias/bypass caps were replaced with upgraded voltage and temperature rated F+T/MOD/CE/Vishay/Nichicon brand electrolytic’s. New 2 Watt Metal Film/5 Watt Cement power dropping resistors were installed for better reliability and lower noise floor. The cathode ballast resistors for V1/V2 were replaced with 3 Watt Cement type units due to heat damage and also the same reasons as above.

The original tubes tested OK but were not the right model for this amp. Although the EL34 is a compatible tube with the 6CA7, there are differences in tone and biasing that make 6CA7 the better choice here. After all it is the tube this amp was designed to use - I’m sure Leo Fender knew what he was doing. The tubes were replaced: V1-V2 = JJ 6CA7 Matched Pair. These were picked for best tone and reliability. The 6CA7's Bias was set to Factory Spec of 25mvDC across each 3.9ohm ballast resistor. All of the original TL082 Op-Amps in the preamp circuits and Effects circuits were replaced with new Texas Instruments TL072 Op-Amps. This was done to circumvent the common issue of 40 year old Op-Amps in these types of MusicMan amplifiers getting noisy or failing. The TL072 is a lower noise-floor replacement for the TL082 and was more commonly used in all of the MusicMan amp lineup. All tube sockets were cleaned with De-Oxit and re-tensioned. The pots were sprayed out with De-Oxit and the amp was cleaned inside and out. A new 3 prong AC cord was installed to replace the worn out original and the Death Cap was deleted rendering the ground switch deactivated. Amp now functions well.