I'm trying to figure out whether my Music Man amp is a 112-65 or a 112-75. The badge on the grill cloth says "112-75 // Seventy-Five", but the badge on the chassis with the model/serial numbers says "MODEL NO. 112-65 // CHASSIS NO. 2275-65 // SERIAL NO. BN12592". Since the only tubes I can see in the back of the amp are a pair of 6L6's (thus no preamp tubes), I'm guessing that this is a 112-75. But it just seems weird that the model number would be incorrect. I haven't seen anything written on the chassis/transformer (although I've never taken the chassis out of the cabinet before), so I don't really know what else to go on here. Also for whatever it's worth, this amp has a phaser circuit instead of a regular tremolo.
I got this one from someone on craigslist a few years ago, so I don't really know anything about where the amp originated.
Here's another image of the
Here's another image of the front to show what I mean.
112-65 or 112-75
Looks like maybe a112-75 since you say it has a phaser... in a mislabelled 2275-65 chassis? Did you confirm the tubes are 6L6?
Hmmm...
Based on your photos here and in your Reverb ad, looks to definitely be a 65 chassis. The Model #, Chassis #, Output #, and Tremolo labeled RCA footswitch jack all point to a 65 chassis.
The 65s ran on 6CA7/EL34 tubes, the 75s used 6L6s. If your tubes are 6L6s, could be someone plugged in the wrong tubes.
Are you sure you have a Phasor? On a 75 the Speed control knob can be pulled out to stop the sweep of the filter. Could it be that you actually have Tremolo that is badly dialed in, so is doing the doubling thing it does when normally turned up past 5?
Is your footswitch labeled Reverb and Tremolo or Reverb and Phasor?
The 65 and 75 cabinets were identical in dimensions, so it's entirely possible someone installed a 65 chassis in a 75 cabinet
Or stuck a 75 model plate on the front of a 65 amp cabinet.
Let us know what you find so we can solve this mystery!
I just reexamined the phaser
I just reexamined the phaser circuit, and it turns out that the speed control is indeed a push/pull pot that does the manual filter sweep like you said. And no, it doesn't do anything like what you described when either the speed or intensity is turned up past 5. The footswitch input on the amp is labeled Reverb/Tremolo. Regardless, though, it certainly doesn't sound like a tremolo.
Well then...
...if you have a Phasor (assuming it came from the factory that way), it should be a 112-75. Certainly possible someone grabbed the wrong chassis or wrong chassis back label when it was being built.
A less likely possibility is that someone put the guts of a 75 amp into a 65 chassis. Or added a phasor circuit to a 65 amp (is that even possible)?
Recap it, clean it up, and enjoy it!
Well then...
...if you have a Phasor (assuming it came from the factory that way), it should be a 112-75. Certainly possible someone grabbed the wrong chassis or wrong chassis back label when it was being built.
A less likely possibility is that someone put the guts of a 75 amp into a 65 chassis. Or added a phasor circuit to a 65 amp (is that even possible)?
Recap it, clean it up, and enjoy it!
Interesting!
A bit late to the party here. Would you mind posting a few more pictures of this unit? I'm interested in the speakers from behind and if it's not too much trouble some pictures of the PCB inside. I understand completely if you don't want to take the chassis out of the amp though. It's more than likely a transition model: The actual metal chassis is identical between 2275-65 and 2275-75. Does your amp have a tube chart inside?
Thanks,
-Lars Verholt