Swapping 110v to 220v Transformer on 65-212
Hi all,
I've got a pretty, mint condition 65 watt 212. Chassis is 2475-65. PI tube. It sounds amazing. It is my main rig. I'm from the US originally but have called New Zealand home for many years. I'm not planning on returning to the US, so it's time to swap out the Power Transformer as I'm not interested in lugging around an external one if and when I start gigging. To that end I've purchased the only replacement 65 Watt PT available today from Mercury Magnetics. The info below is for all those dealing with PT replacement and should be taken with a grain of salt in that: 1. I'm not an amp tech 2. I have yet to install my replacement PT.
The following is what I've gathered over the past few days about the Transformer situation with Musicman amps of this time period
History:
Musicman amps (like mine, ie mid to late seventies with a PI tube) had one type of Power Transfomer stamped 1-65 early on. This supplied Hi/Lo power, switched in the transformer's primary. Later they changed Hi/Lo switching to the Secondary. This later model transformer is stamped 100-65. This swap of transformer required rewiring the front switch to ON/OFF and the rear Standby become HI/Standby/Low and was detailed in Service Bulletin #4, available in the Downloads section of this site along with Schematics. Many people however (like the previous owner of my amp) never swapped the transformer. Why would you if the amp worked perfectly well?
Interesting to note: I used to jam with a guy in the late 90's who bought a 4-10 (don't remember 65w or 130w) that had undergone the rewire and swap. His amp had a metal badge stamped on the front switch that said 'On/Off' covering the old 'Hi/Off/Lo' markings. Same thing on the rear standby switch, with 'Hi/Standby/Low' printed there. Yet I've never seen another Musicman like it, ie one that has had the PT replaced and switches rewired.
What Musicman Transformers are Available Today:
Apparently Mojotone used to build replacement versions of the PT (not sure if they were 1-65 or 100-65!) but that ended years ago. Other threads mention TAD (Tube Amp Doctor) as a potential source - but unless they have products not listed on their site, the only Musicman transformer they build these days is at Output Transformer for the 2275-150 variant. They used to offer a PT for the HD130 (accommodated Hi/Lo switching) but not anymore.
Currently, in 2026, Mercury Magnetics offers both Output and Power Transformers for the 65 watt and 130 watt variants. It is important to note, however, that these have only ONE power setting available.
Mercury Magnetics website lists a 2275-65 Power Transformer (both 110v and Export) labeled 'Drop-in Upgdade!' - which is not entirely accurate. I have yet to install mine, but the first thing I noticed on arrival was there aren't enough wires to offer Hi/Lo switching. Oh well - I would have purchased in anyway. My main concern isn't Hi/Lo switching, it's not having to carry around an external transformer!
There is one main output voltage (red and red/yellow) on the secondary and it is 245V. There are also 2 oranges (labeled 'Accessory') and 2 green wires labeled 6.3V filament.
Also important to note, Mercury Magnetics also sell Output Transformers for both the 65w and HD-130w models.
Install:
At this stage I'm confident that I (or an amp tech, haven't decided yet) will get the new transformer installed and running. But this amp will always be in what used to be considered 'Hi Power' mode, ie 65 Watts. That's fine by me - though I'm not sure I'd want Hi Power mode in an HD 130 all the time! I've got an HD130 as well, which I may also convert at some stage but I may see if it's possible to use a PT meant for a 65w. Not sure if that will work yet. I'd prefer if the HD-130 was at the same output level as the 65w. Mysteriously, Mercury Magnetics spec sheet for the HD130w PT outputs a single secondary power tap rated at 265v. Not sure how that works as the 65w and 130w PT's are only 20V apart in their output!
Also important to note for those seeking to install a replacement PT (either 110v vs 220v) - you don't need to pay attention to Service Bulletin 4 as far as I can tell. Service Bulletin #4 was about moving Hi/Lo switching to the Secondary and the rear of the amp. No point if there is no Hi/Lo switching! Having said that, the most I've done on an amp is recap it!
It seems when Mercury Magnetics engineered the replacement transformer they decided to simply skip Hi/Lo switching altogether as the simpler alternative. So if you're amplifier, like mine, has a 1-65 OT and never underwent the SB #4 rewire, you can just keep your wiring the same more or less. Obviously the front switch has to be adjusted to on off, but the rear Standby can remain Standby.
The forum isn't terribly active at present as far as I can tell, but if anyone has a piece of advice or a suggestion to make before I proceed with the install I'd be grateful for it.