Popping sound from pre-amp tube socket.

[harkkam08]

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

[harkkam08]

Hey guys I got it too work.

It sounded great, the Larmar worked perfectly, I played for about 10 minutes, and engaged the fuzz pedal and about one minute later the amp died. No sound no hiss.

I then turned treble middle and bass to half way and then heard no hiss like I was before I started playing.
It kind of faded out with the volume getting lower and lower and the nothing in a mater of 2-3 seconds



Help needed I hope my amp isnt dead.

I took some voltages and here is what I got

V1:
pin 1= 190
pin 2 = 0
pin 3 = 1.479
pin 4/5 = 3.35 AC
pin 6 = 198
pin 7 = 0
pin 8 = 1.4
Pin 9 = 3.35AC

V2:
pin 1 = 8.4
pin 2 = 3.5
pin 3 = 2.7
pin 4/5 = 3.35AC
pin 6 = 306
pin 7 = 8.4
pin 8 = 12
pin 9 = 3.35

V3:

pin 1 = 231
pin 2 = 25.5
pin 3 = 41
pin 4/5 = 3.35 AC
pin 6 = 227
pin 7 = 26.7
pin 8 = 41
pin 9 = 3.35

V4:

pin1 = 33.4 mv
pin2 = 3.35AC
pin3 = 499
pin4 = 495
pin 5 = -46
pin 6 = 498
pin 7 = 3.35AC
pin 8 = 33.4mv

V5,V6,V7

had almost the same values for each pin.

For V5, V6, V7 pin 1 and 8 did read 33.4 mv as well.


I think v2 might be bad getting only 8 volts on pin 1

[harkkam08]

Okay got it working again.



Turns out to be just a bad V2 tube. Plugged in another and now she is singing. Played her for half an hour channels jumped, dimed on both channels using the Lar/Mar

She sounds so good wow. Threw a fuzz pedal and just sounds amazing.

Now to test my neighbors patience and figure out how loud is too loud

[54strat]

V-2 spot is rough on new production tubes because of the higher voltage in that position. Most Russian stuff can not handle it. JJ/Chinese/or NOS your safest choices there.

[harkkam08]

V-2 spot is rough on new production tubes because of the higher voltage in that position. Most Russian stuff can not handle it. JJ/Chinese/or NOS your safest choices there.

Well whats ironic is that the JJ was in V2 the one with the kit but i swapped it out with a electro harmonix russian so we'll see what happens. I am gonna record some clips and hope to get some feedback

[harkkam08]

Just curious guys if I wanted to increase my plate voltage to 550 or > 500 how would I do that?

IS that even possible?