Music Man RP 65: Repair, analysis, bias setting and sound demo 

Wow, that phaser at 25:20 is just right! The sound of the 70s.

Thanks for sharing. Great to have more info about these amps.

There was one of these in a rehearsal space I used to frequent. Favourite amp ever.

I just stumbled across your channel. Nice to see a fellow tech giving MM amps some love. I think they’re wonderful. I got one just because of Johnny Winter. He said in an interview once that he always kept the Bass and Middle controls on zero, and the treble turned to 10 on his MM amps. That’s insane.

I had one of those in the early eighties. I loved it. Worked great with the few pedals we had then. Very loud. Durable, never let me down, not once. Very well made. Wanted a Marshall, got a Marshall. Loved that Amp though. 30 years later I got another one. It's here now next to my Marshall

Your guitar playing didn"t torture my ears, all th opposite. Very pleasant, well done, sir !

Nice work, glad I found your video 👍🏽

First time viewer here, thanks for putting this up. Not many tube amp guys want anything to do with op amps or transistors.

Thanks for this! A MM RD210 2 x 6CA7 and square Eminence 10" were my first "real" amp and served me well through many recordings and occasional live performances. I often recorded in my flat and had to play quiet but the built-in distortion circuit did a great job to mimic a "swetting" amp, at least in my recordings.

I have this exact amp model and the original speaker had a blue/silver Music Man logo on the sticker, so the Celestion one is a replacement for sure.

Clapton played a Musicman HD-130 reverb modded for a bit more gain than stock. The early version had a 12ax7 phase inverter tube and no reverb, like a fender bassman. I have both, the earlier one sounds better to my ear. They came with sylvania 6CA7 output tubes.

My first real amp was a RP 100 head- wish I still had it

I have one of these. It’s worthy of being a collector.

I had 2 Music Man amps back in the day (mid 80's). A 65 Reverb head and an HD 130 head . Both were crazy reliable and sounded great thru my 4x12 marshall cabs. I wish I still had them.Today I have a Mesa Boogie V combo and a Fender Blues Jr.

Hey Martin, good to see a MM maintenance video, they are quite unique and fantastic pedal platform amps nowadays at a still accessible price on the used market. MM's never came with Celestions. Early on they came with Ceramic Jensen's. Then Ceramic square back eminence (most common). Sometimes with Eminence alnicos. The JBL DF's and EV 12L were available as upgrades. They would buy these speakers as OEM and slap a music man sticker on them usually. If you goto reverb and search up music man combos, you'll see the array of speakers they came with 👍

First time at your channel. Thanks for sharing. I hit the subscribe button too.

Wow, that sounds gooood. :) thnx

I have owned two MM amps...both the 212 HD model....and I believe both were either 120 watt or 130 watt....mine had a huge amount of headroom and were impossible to push into distortion because they were so FKN LOUD....I eventually bought a Soldano 2 channel foot switchable pre-amp and had an extra input that sent the Soldano straight to the MM's output section.....both MM amps had broken reverb when I bought them...the first had the entire reverb unit and enclosure bag removed from the bottom of the combo enclosure.....the second had the entire reverb still intact , but I discovered that the reverb pan had a small half moon cut into it for some of the circuitry wiring to pass through.....the reverb pan itself was being hung on springs , my guess is to lessen stage vibrations from transferring to the springs carrying the guitar signal , but when the amps were in a bumpy van with bad shocks on the way to a gig , or being mishandled by idiots , the reverb pan would shake like a hammock on a boat in a storm , and the sharp half -moon edge on the side would slice the circuitry wire because they were being thrifty and used short wires that had tension on them....a longer wire without the tension would just get pushed aside by the swinging reverb tank....I then understood why the first one I bought had the entire reverb unit removed ....I bought an Alessis microverb that I patched in after the Soldano instead of rescuing the original reverb.....both amps had Celestion Vintage 30's in them .....this rig sounded absolutely amazing !

I have a 2-12-65 pre amp was a Leo design his last one 8m gold. But I've never seen any literature on that model.

I bought a really clean used. 112. 65 watt recently at a pawn shop for $150. Late 70s or early 80s. Speaker had been replaced with a cerwin vega. Loud and proud. A fender made better !!! Clean great for most styles. Clean lead amp

I had a 65 watt, 2X10 and it was the flattest sounding, most toneless amp I've ever owned.

I have this amp. Has a MM labeled Rola ceramic speaker.

Very nice video. 👍 I had a MM amp 20 years ago. It had a SS preamp with quite nice tremolo and a pair of 6L6 tubes as output stage. No phaser. It sounded very nice and balanced. I cannot recall the exact model number, or what speakers it had. AFAIK EL34 tubes surely can be run at those very high 800V plate voltages, and you can get almost 100W out of a push and pull pair, but they usually were supposed to run at almost pure class B and were used for example as PA amp output stage. The EL34 tube can handle that kind of voltages but bad quality or dirty tube sockets can't without arcing because of the pin order which is not optimal for ultra high voltages. 🤓

My mate had a 50w 1x 12...cream tolex though. Lovely amp heavy as, but built to handle the back of vans... Joe Strummer used em too. Nice job mate!

Brilliant amps had this model just got to heavy over the years 👍

I owned the 2x12 version of this amp. The salesman at the music store talked me out of buying the Fender Twin Reverb that I’d always wanted. I regretted that decision every single day until I finally sold it to buy a Marshall JTM30 30 watt 2x10 combo amp which absolutely blew the door off this amp.

Stanton-Gibsons were hybrid, 60's design I think. They're kind of neat, built in Maestro effect kind of phaser? Reverb tank too.

Interesting, and effective testing. I've got a Music Man 112 RD. Nice sound, but I always thought it had a bit too much self noise. After hearing how quiet you got the Amp on your bench, I think there's probably something wrong with mine.

I remember when they came out nobody wanted them. Marshall ruled the day.

Joan Jett's choice too!

The schematic that you showed is for a different amp that is using 6L6 output tubes. These can't be operated with plate voltages near 800V. The RP 65 runs the output tubes in class B, with 25mV across 3.9 Ohms the quiescent plate current is only 6.5mA. Did you measure the voltage at the cathodes? I bet it is at least +50V. So the output tubes are stressed lower than in class AB amps. By the way, the phase splitting is done by IC8, not by the cathode driver transistors. I own a MM HD130 (the early version with a phase inverter tube) since 1980, the original EL34s were labeled Telefunken.

I have one with 2 10" speakers

Peavey made hybrids before MM.

That soldering iron I would use for rain pipes on the roof

The Celestion is definitely not original. These came eminence custom order speakers.

Your job was ok, but your analysis of the power amp is wrong, sorry to say that. I am the owner of the model 2165 rp. It contains the pcb named "GP2". My amp was made in January 1980. The pcb of your amp looks different; it may be the "GP3" version. There ist not much difference electronically. I call these amps the "NEW", the "MODERN" MusicMan powerAmps. These amps are not anymore "hot", the powertubes are surprisingly "cold". These amps don't copy anymore the "Williamson" design, the basis of all the Fender and Marshall Power-Amps since the end of the 1940s. They use a new invention - a power transistor working as a "floating cathode resistor". The old Williamson design was used in the "early" MM Amps. These amps had a "normal" phase-splitting-design, featuring both triodes of a 12AX7 (ECC83). The splitted signals were fed into the CONTROL GRID of the EL34 (6CA7) or 6L6; this control grid had to be very negative (depending what type of tube was used) to control the "bias" (the current through the tube in idle state). The current through a 6CA7 or 6L6 in a typical "Williamson-Amps" is something between 30 to 40 mA. The new design is revolutionary different: The control grid is not used anymore. A positive voltage of +22 Volts is there (look at the 220 Ohm resistor, it is there for safety reasons). The signal is splitted by the two op_amps in IC8. The Motorola Power transistors JE 1692 act as "floating cathode resistors". The current through the Emitter-Collector path is "dancing" depending on the signal-voltage at the BASIS of these transistors. This was a VERY NEW design - possible because of the availability of these new transistors. The "bias" (the current through the power-tubes in idle state) is only between 6 to 7 mA (25 mA / 3,9). The "new design" is also found in amps with 6L6 power tubes - for example in my second MM Amp, the 2475-75 amp with two 12 inch speakers.

definitely not the original speaker

The voltage across the resistor (the bias setting) on ​​that and other Music Man amps varies depending on the master volume setting.