[1000mp] feedback from rf or speaker in MH31 mike

[Bill D]

Hello; I've exhausted my capability to correct the problem of  feedback 
through the mike on 80meters when using more than 50 watts of power. I have 
tried adjustments on mike and can overcome feedback when positioning the 
mike gain at about 9 o'clock or less and alc meter shows little or nothing 
and PO meter is no longer accurate. I tried by passing (disable) tuner and 
still able to transmit with 1:0 or less SWR. Still the effect on the 
microphone and unable to increase power beyond 60 watts. Tried manual tuner 
and no difference. Tunes OK but mike feedback still a problem. Re-grounded 
unit and new balun. All looks OK, but not on 80 meters. Problem does not 
occur on other bands except when using the Ameritron 811H amp with manual 
tuner (3k Roller Inductor) I cannot get the power to the antenna from the 
amplifier and load and plate adjustments must be retuned each time I use 
amplifier.
Too much text, I apologize. But I've studied help sites on internet for 
1000mp mk V owners as well as read the manual  many times and still have the 
mike problem on 80 meters with more than 50 or 60 watts . Wonder if anyone 
has had this problem and how it was solved? Thanks much