Rocktron starts buzzing when I play it on keyboard

Try different cables. That would be the most simple and cheapest fix.

Are all the tubes lighting up? they should glow like dim light bulbs. If not, replace them with the same model type (12ax7, or EL34 for example).

Often there are two fuses, one to protect the speaker and another to protect everything, it sounds like the latter fuse may be burned out. take it out and take it to radio Shack for exact replacement.

Start by unplugging anything attached to the amp to eliminate simple things such as a broken shield on an input cable.
If you still have the pronounced hum with nothing connected, then the amp's power supply may have a failed filter capacitor or diode bridge. Either of those would have to be sought by a tech with the right gear.

All amplifiers make a little bit of noise (hiss) but it is normally slight and drowned out by playing. However, assuming that this is not normal system hiss, here are a few simple steps to try and locate the source of the problem by process of elimination.

1. SAFETY FIRST - a common cause of a humming or buzzing sound can be a lack of earth (grounding) on the mains supply. With a 240volt AC supply this hum will be at 50hz (in the UK) - frequency may vary in other countries but should be similar. Check the earth first because of risk of electric shock. Until you are satisfied that this is not the cause of the problem DO NOT touch any metal parts of the amp. Remove the mains lead and try a different one. Try plugging the amp into a different mains outlet socket (preferably one on a completely different circuit).
2. Turn off other electrical equipment in the vicinity that may be causing interference. Move the amp a bit, try rotating it by 90 degrees to change relationship to things like mains electric cables in the floor.
3. If you are using the line-out socket to give a feed to a mixer, slave amp or p.a. system unplug this. Sometimes double earthing (through the mains lead of your amp AND the mains lead of the MIXER / PA) will cause an 'earth loop' due to a different resistance at each end. Putting a DI box with an 'earth lift' in between may eliminate this problem. Alternatively there are little gadgets you can buy to do this (I found one intended for car audio systems on Amazon that works very well)
4. Unplug any instrument leads - to eliminate possibilities of interference affecting cables, effects pedals or guitar pick-ups. Also unplug the foot-switch.
5. If that stops it plug a lead in without a guitar on the other end - does the noise return? If yes change the lead. If no plug the guitar in.
6. Try moving the guitar in relation to the amp (turn it around 90 or 180 degrees) - this will be pick-up to amp power supply interference.
7. Does the sound get better or worse if you touch metal parts of the guitar with your hand? This may be a screening issue within the lead or the guitar itself.
8. Try turning all the individual channel tone and gain controls to zero, turn off any effects on the amp panel. If that eliminates it only turn up the controls on channels that you are actually using.

You say the "tubes are fine" I take it that you have either replaced them with new or used a very sophisticated tester on them. A heater-cathode short might cause the symptom. There are a bunch of tests I would want you to run alnd get back to me with the results.

Heat up the amp but DO NOT play anything into it for the usual failure time or more and they start to play i... did hum occur WITHOUT playing? With all volume controls down does the hum occur?

The right tools is an oscilloscpe to fing out if the filter caps are good. These are C31, C33, C35, C36.

With hum present in failed stater, plug in a grounded plug into the power amp in jack... if hum is stiil there, check the +/- 16 volts regulating Zener for ripple. get schematic here:

http://elektrotanya.com/fender_hot-rod-deluxe_sch.pdf/download.html

You are probably very near a powerful AM transmitter. This is a shielding problem and use of a better quality audio cable between the keyboard and the Talk Box might help as well as CHANGING the length of the cord. Length afects how good an antenna the cord is.

One could put a bypass capacitor in the Talk Box as what you are hearing is "rectification" of the radio station in the high gain of the inout circuit of the talk box... one or two capacitors would likely fix it... I would try 330 Pf caps first right where the cord comes into the box between the signal and ground points.

If the amp is quiet with cables unplugged at the same settings as observing the buzz, the amp is OK.

In this case, cables and/or shielding and wiring in the guotar is suspect.

Guitar pickups are sensitive to magnetic fields and you can search out these fields by moving and orienting your guitar to find maximum buzz.

If the amp has objectional buzz with teh cables UNPLUGGED then the amp needs servicing. Filter capacitors among other things are suspect.

If you unplug the guitar cable and STILL get the hum, the unit has a defect... return under warranty.

If the hum goes away when you unplug the cable, replace the cable and see if new cable fixes the problem. If it does, the cable has a bad shield.

If the cable didn't cure it, then the guitar has a defect. Remember that some guitar pickups are sensitive to the magnetic fields from the amps... only cure is to either use humbucker types or be a distance away from the amp.

First and foremost , check your signal chain. By that, i mean put the pedal aside, ...just unhook it and take it out of your signal path. Using the same cables , guitar , amp, other pedals - borrow a friends MT-2 if you can get one , and try THAT to see if THAT works , OR any other kind of distortion pedal. If another one works ok , it's YOUR MT-2. Boss pedals are pretty rugged , but sometimes the little actuator (on/off switch) underneath the treadle (where you push your foot down) will become faulty. That's a high-gain pedal - are you using a basic Strat or other single-coil pickup guitar? If so , are you playing close to any flourescent lights? SIngle coils are noisy around those lights. Will cause a hum / buzz if using a heavy dist. pedal. You can check that by moving around as you play.

If the buzz disappears when you unplug the cable from the amp. check your cable.
If the buzz disappears when you unplug the cable from the instrument, there's something thay may have come loose inside the instrument.
If you unplug the cable from the amp., and the buzz persists, you'll have to have a competent tech. check your amp.