M - MA 230
This modification may be incorporated in MA 230
units to increase the overall gain.
This modification may be incorporated in MA 230 units with hum introduced when the H.F. filter switch is depressed.
Installation of a 4 section volume control.
M - MI 2
To eliminate any shape other than a dot when in the "TEST" position.
M - MI 2 & MI 3
Power transformers have failed in some M1-2/M1-3 units due to intermittent
shorts in the 6W4 HV rectifier tube. These shorts are caused by cathode flaking in the 6W4.
M - C 8, C 11, C 22
Replace the selenium rectifier with silicon rectifiers. These silicon rectifiers have much longer life.
M - C22
To insure long life of festoon pilot lamps, always replace them in pairs in the C22. The two lamps are connected in series. As the lamps age their resistance increases. If only one lamp is replaced the older lamp will have higher resistance than the new lamp. This will cause more voltage to be present across the older lamp. The higher voltage will cause the older lamp to burn out more quickly than it otherwise would.
M - C 24
Some controls have developed a noise when rotated. Adding the springs to ground the shafts prevents this condition.
Adding four grounding springs to the shafts of the Volume, Balance, Bass and Treble controls.
M - MA 230
Tightening the transformer mounting screws to eliminate buzzing.
M - MR 65B, MX 110, MR 67
To allow adjust control for instant correction of tube and circuit variations. This will insure proper MPX indicator light operation.
M - MR 71
This modification increases stereo separation on MR 71 tuners to better than 35 db separation.
M - MX 110
Popping noise from the speakers when the switch controls on the MX110 are operated can be caused by "leaky" .1 MFD disc ceramic coupling capacitors.
M - MAC 1500
To increase audio gain in all input positions. This modification changes the volume control taper to give about 8db more gain. (It does not increase the gain in the full volume position.)
M - MX 110 Z and X series
This modification eliminates both the "opening" of the tuning eye after warm up, and the muting threshold change with tuner warm up.
M - MC 2505
Although the MC 2505 is rated at 50 watts (sine wave) per channel, it will normally put out at least 75 watts per channel. However, it is possible to drive the amplifier even harder than this. The following modification will improve the power output capabilities when the amplifier is loaded with a mis-matched load. It will also eliminate the possibility of any noise from the power supply being heard through the speakers when the amplifier is turned on and off.
M - MA 5100
The modifications described will increase the RF suppression capabilities of the amplifier.