Popping sound from pre-amp tube socket.
Posted: Wed Feb 02, 2011 4:54 pm
Hey guys I just finished building a 100 watt amp. Has the LarMarr PPIMV
Pictures can be found here.
http://forum.metroamp.com/viewtopic.php?f=28&t=34312" onclick="window.open(this.href);return false;
BTW the selector switch is wired correctly I flipped the direction of it because I cut the wires too short so the green still goes to the 16 ohm pin etc.
Sorry for starting another thread but I figured my post in it wouldnt get looked at by as many people.
Okay So I flip the main switch and the light stays on constantly the main fuse does not blow and the pre-amp tubes glow.
Then I check the heater voltages and I am getting 3.5V AC on pin 7 and pin 2 from the output and pre-amp tube pin 4/5 and pin 9.
Then I check the bias at the 5.6k resistors and I get -50.1V so that seems good. I get that on each 5.6k resistor on the output tube.
Now I am assuming that the voltage chart in the kit instructions are taken with the Standby switch on, in other words HT running. Only the preamp tubes have been installed.
So I flip it from standby to on.
However after about 3-4 seconds I heard a pop like electrical sounding noise come from the v1 preamp tube socket. Then about 5 seconds later I hear the same noise in the preamp v2 tube socket.
Thats when I shut it off.
I checked both fuses with a continuity meter and they are good they have not blown.
I am worried to turn it on again that I might damage something.
Thanks guys for all your help.
Edit: I checked the pins on the standby switch and I am not reading any voltages. Hmm maybe bad connection.
Edit 2: I didnt select AC voltage I am getting 190 V on the switches.
Edit 3: I wired the bass and middle pots incorrectly. I connected lug 1 of bass to lug 2 of middle instead of lug 3
Pictures can be found here.
http://forum.metroamp.com/viewtopic.php?f=28&t=34312" onclick="window.open(this.href);return false;
BTW the selector switch is wired correctly I flipped the direction of it because I cut the wires too short so the green still goes to the 16 ohm pin etc.
Sorry for starting another thread but I figured my post in it wouldnt get looked at by as many people.
Okay So I flip the main switch and the light stays on constantly the main fuse does not blow and the pre-amp tubes glow.
Then I check the heater voltages and I am getting 3.5V AC on pin 7 and pin 2 from the output and pre-amp tube pin 4/5 and pin 9.
Then I check the bias at the 5.6k resistors and I get -50.1V so that seems good. I get that on each 5.6k resistor on the output tube.
Now I am assuming that the voltage chart in the kit instructions are taken with the Standby switch on, in other words HT running. Only the preamp tubes have been installed.
So I flip it from standby to on.
However after about 3-4 seconds I heard a pop like electrical sounding noise come from the v1 preamp tube socket. Then about 5 seconds later I hear the same noise in the preamp v2 tube socket.
Thats when I shut it off.
I checked both fuses with a continuity meter and they are good they have not blown.
I am worried to turn it on again that I might damage something.
Thanks guys for all your help.
Edit: I checked the pins on the standby switch and I am not reading any voltages. Hmm maybe bad connection.
Edit 2: I didnt select AC voltage I am getting 190 V on the switches.
Edit 3: I wired the bass and middle pots incorrectly. I connected lug 1 of bass to lug 2 of middle instead of lug 3