Hey all,
I just finished assembly on a little m49 clone that I built into an mxl 990. Been getting into these mxl mods lately!! Fun format... Anyway, i am having some spitty noise in the design. Sounds like bad Hi-Z section or a bad tube... I cleaned all the high z parts with 70% ipa (except the styroflex).
I am curious if the relay I used to cut the back diaphragm off in cardioid is giving me issues. I used DS1E-S-DC6V relay. I have a diode between +/- coil terminals. I have the common terminal jumped to the point where the back capsule should be connected to the circuit on a ptfe isolated turret... The Normally connected pin is connected to the rear diaphragm and the Normally open pin is floating. When the relay closes it switches the common terminal connection to the NO pin and disconnects the NC pin. The common pin, NC and NO pins are all floating. The only soldered pins are the coil pins. Is there anything else I need to consider with this implementation?
Another potential issue is that when installing the tube, I did not heatsink the tube leads when soldering. I was very very quick and careful when soldering to the pads... but perhaps I introduced a micro crack in the glass...
I can test the relay theory by simply removing the floating bus wire between the common pin and the ptfe turret leading to the grid through the 1000pf styroflex...
Testing the tube? Well I am going to let it burn in a bit longer before checking with the noise... I could always swap it out for a different tube as well...
Thanks for any advice…
CHEERS, Eric
. 
I just finished assembly on a little m49 clone that I built into an mxl 990. Been getting into these mxl mods lately!! Fun format... Anyway, i am having some spitty noise in the design. Sounds like bad Hi-Z section or a bad tube... I cleaned all the high z parts with 70% ipa (except the styroflex).
I am curious if the relay I used to cut the back diaphragm off in cardioid is giving me issues. I used DS1E-S-DC6V relay. I have a diode between +/- coil terminals. I have the common terminal jumped to the point where the back capsule should be connected to the circuit on a ptfe isolated turret... The Normally connected pin is connected to the rear diaphragm and the Normally open pin is floating. When the relay closes it switches the common terminal connection to the NO pin and disconnects the NC pin. The common pin, NC and NO pins are all floating. The only soldered pins are the coil pins. Is there anything else I need to consider with this implementation?
Another potential issue is that when installing the tube, I did not heatsink the tube leads when soldering. I was very very quick and careful when soldering to the pads... but perhaps I introduced a micro crack in the glass...
I can test the relay theory by simply removing the floating bus wire between the common pin and the ptfe turret leading to the grid through the 1000pf styroflex...
Testing the tube? Well I am going to let it burn in a bit longer before checking with the noise... I could always swap it out for a different tube as well...
Thanks for any advice…
CHEERS, Eric
. 
