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I received a new Laney Ironheart IT120H Guitar Amp that had steady Static Noise coming out of the loudspeakers. I’ve never been inside one of these. I downloaded the Owner’s Manual, which had a block diagram to work from. I found after working the front panel controls, that none of the controls appeared to be involved
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I removed the chassis from the cabinet, and set it on my service cradle, somewhat precariously balanced on the edges of the cradle. After removing the driver tube V4 from the chassis, I still had this static noise, so concluded the source of the noise was NOT from the preamp circuits, unless being coupled thru the power supply.
I next powered down, let the power tubes cool down, and decided to remove one pair of the output tubes. That’s when I found the tube clamps were EXTREMELY stiff, and usually, one can depress the clamp wings with my fingers while using my other hand to carefully remove the tube. NOT SO with these clamps. These were so tight, I’d really need a second person to assist in order to get the tubes out. But, I didn’t have anyone about to assist, so struggled the best I could. Finally got the outside pair out, leaving the inside pair of tubes in place.
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The static noise continued. I then replaced the inside pair and put the outside pair back into their outside sockets. No longer had the static noise. I moved the left tube V12 over to the V11 socket, and again had the static noise. I marked that tube and then struggled to get that tube out to try the one from V9 in that socket. I had the noise again, from a tube that was NOT yielding that static noise. That seemed to point to the V11 tube socket and/or components. 1.5k 1/2W CF Grid Resistor, 470 ohm 5W bathtub screen resistor, and wrapping around that tube socket were three 1N5408 3A/1KV rectifier diodes (reverse biased from GND to the Plate circuits).
Just to be sure the other tubes weren’t the source, I went to remove the tube installed in V11, when the chassis slipped off the service cradle and broke the other pair of Ruby 6L6GC power tubes (matched set) sitting below. Sigh………..
That ‘accident’ was caused by these extremely stiff tube clamps, having so much effort needed to release the tube from that V11 socket. I removed the power tube PCB, replaced the 1.5k grid resistor, as well as the 470 ohm screen resistor. I debated replacing the 1N5408 diodes. Now, only having one pair of output tubes, I had to go fetch a matched set of J/J 6L6GC’s from the Guitar Dept.
Also, with the clamps removed, I did my best to try and reduce the holding force they were exerting on the tube bases and did manage to weaken them enough to install the replacement tubes with the new tubes.
The replacement J/J tubes I re-biased for 30mA ea, and no longer had the static noise. I still suspect the 1N5408 diodes, though the grid resistor body was in contact with one of the diode bodies. I also unsoldered and re-soldered the tube socket in question, having tracked the noise source to that socket and perhaps the support components.
I didn’t see any mfgr name on the clamps. I looked at what the Belton clamps look like, but those have a slotted hole, while these did NOT.
The amp is back together and no longer making that static noise. Not sure if it was from the grid resistor or from solder joints on that tube socket. Problem solved for now. No idea WHOSE tube clamps those are, but sure not a fan of these! This clamp is similar to what's installed, but NOT as stiff. I should have looked to see what the metal thickness was, but it is THIS style, and I'm sure I've come across them before, I think in Mesa amps. Definitely hurt your fingers trying to get a tube removed.
I removed the chassis from the cabinet, and set it on my service cradle, somewhat precariously balanced on the edges of the cradle. After removing the driver tube V4 from the chassis, I still had this static noise, so concluded the source of the noise was NOT from the preamp circuits, unless being coupled thru the power supply.
I next powered down, let the power tubes cool down, and decided to remove one pair of the output tubes. That’s when I found the tube clamps were EXTREMELY stiff, and usually, one can depress the clamp wings with my fingers while using my other hand to carefully remove the tube. NOT SO with these clamps. These were so tight, I’d really need a second person to assist in order to get the tubes out. But, I didn’t have anyone about to assist, so struggled the best I could. Finally got the outside pair out, leaving the inside pair of tubes in place.
.
The static noise continued. I then replaced the inside pair and put the outside pair back into their outside sockets. No longer had the static noise. I moved the left tube V12 over to the V11 socket, and again had the static noise. I marked that tube and then struggled to get that tube out to try the one from V9 in that socket. I had the noise again, from a tube that was NOT yielding that static noise. That seemed to point to the V11 tube socket and/or components. 1.5k 1/2W CF Grid Resistor, 470 ohm 5W bathtub screen resistor, and wrapping around that tube socket were three 1N5408 3A/1KV rectifier diodes (reverse biased from GND to the Plate circuits).
Just to be sure the other tubes weren’t the source, I went to remove the tube installed in V11, when the chassis slipped off the service cradle and broke the other pair of Ruby 6L6GC power tubes (matched set) sitting below. Sigh………..
That ‘accident’ was caused by these extremely stiff tube clamps, having so much effort needed to release the tube from that V11 socket. I removed the power tube PCB, replaced the 1.5k grid resistor, as well as the 470 ohm screen resistor. I debated replacing the 1N5408 diodes. Now, only having one pair of output tubes, I had to go fetch a matched set of J/J 6L6GC’s from the Guitar Dept.
Also, with the clamps removed, I did my best to try and reduce the holding force they were exerting on the tube bases and did manage to weaken them enough to install the replacement tubes with the new tubes.
The replacement J/J tubes I re-biased for 30mA ea, and no longer had the static noise. I still suspect the 1N5408 diodes, though the grid resistor body was in contact with one of the diode bodies. I also unsoldered and re-soldered the tube socket in question, having tracked the noise source to that socket and perhaps the support components.
I didn’t see any mfgr name on the clamps. I looked at what the Belton clamps look like, but those have a slotted hole, while these did NOT.
The amp is back together and no longer making that static noise. Not sure if it was from the grid resistor or from solder joints on that tube socket. Problem solved for now. No idea WHOSE tube clamps those are, but sure not a fan of these! This clamp is similar to what's installed, but NOT as stiff. I should have looked to see what the metal thickness was, but it is THIS style, and I'm sure I've come across them before, I think in Mesa amps. Definitely hurt your fingers trying to get a tube removed.
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