This amp uses DC for the preamp heaters, so the caps/diodes you replaced were all part of that circuit. Makes sense that it's quieter afterwards, good stuff 👍
Following some advice I found on a amp repair board I'm going to be replacing mine with 1000ohm 5w 1% resisters, and did not even think about replacing the diodes, got those on order now. Thank you for the video!
@@clintronicsrva So adding the 1000Ohm resister as this other individual is saying that he does for all his replacements of screen resisters on JSX and XXX v2 power boards is a bad thing then? I apologize for my ignorance here, I'm just getting in to the world of amp repair, I already recapped the power supply board but used all Nichicon 105 degree C caps instead of the 85c IC caps that were on there. If I need to rebuy the resisters I would rather do it right and if making that a 1400 Ohm circuit is a bad thing, I'll get the 700 Ohm 5w 1% T resisters.
So I talked with one of my buddies that literally designs this stuff for the industry, he went over the schmatic with me and he said that the replacement that I have ordered should be much netter than what is in there, but it will affect the overall Bias of the tubes, I run in the 70% area in regards to the plate current so given the available range I should be able to hit my desired bias of 36mv with the 1000ohm 5w 1% resistor. I'll update ya with actual results after I do the replacement, I ordered the diods as well and will check those after I dig in but I think they are good.
@@LexJones Here's what the Bing AI has to say. Let me know how your experiment goes. BING AI: If you change the screen resistor from 1100 to 1400 ohm, the output power will decrease slightly, but the screen voltage will increase. This will make the EL34 tubes run hotter and may shorten their lifespan. The tone of the amplifier may also change, depending on how much the screen voltage affects the plate current and the distortion characteristics of the tubes. Some people may prefer a higher screen resistor value for a smoother and more compressed sound, while others may like a lower value for a more dynamic and punchy sound. It is a matter of personal preference and experimentation.
@@LexJones Here's what the google AI has to say: If you change the screen resistor from 1100 to 1400 ohms, the output power of the amplifier will decrease. This is because the screen resistor controls the current flow to the screen grid of the EL34 tube, and a higher resistance will result in a lower current flow. This will reduce the power dissipation in the tube, but it will also reduce the output power. The amount of change in output power will depend on the specific amplifier and the amount by which the screen resistor is increased. However, in general, increasing the screen resistor will reduce the output power by about 20%. In addition to the change in output power, increasing the screen resistor can also affect the sound of the amplifier. A higher screen resistor will typically result in a darker, warmer sound with less high-end sparkle. This is because the screen resistor affects the bias point of the tube, and a higher screen resistor will result in a more biased tube.
This amp uses DC for the preamp heaters, so the caps/diodes you replaced were all part of that circuit. Makes sense that it's quieter afterwards, good stuff 👍
Following some advice I found on a amp repair board I'm going to be replacing mine with 1000ohm 5w 1% resisters, and did not even think about replacing the diodes, got those on order now. Thank you for the video!
The 700 ohm resistors are fed by a 400 ohm resistor on the power supply board in series (R64), so that makes the circuit 1100 ohms
@@clintronicsrva So adding the 1000Ohm resister as this other individual is saying that he does for all his replacements of screen resisters on JSX and XXX v2 power boards is a bad thing then? I apologize for my ignorance here, I'm just getting in to the world of amp repair, I already recapped the power supply board but used all Nichicon 105 degree C caps instead of the 85c IC caps that were on there. If I need to rebuy the resisters I would rather do it right and if making that a 1400 Ohm circuit is a bad thing, I'll get the 700 Ohm 5w 1% T resisters.
So I talked with one of my buddies that literally designs this stuff for the industry, he went over the schmatic with me and he said that the replacement that I have ordered should be much netter than what is in there, but it will affect the overall Bias of the tubes, I run in the 70% area in regards to the plate current so given the available range I should be able to hit my desired bias of 36mv with the 1000ohm 5w 1% resistor.
I'll update ya with actual results after I do the replacement, I ordered the diods as well and will check those after I dig in but I think they are good.
@@LexJones Here's what the Bing AI has to say. Let me know how your experiment goes. BING AI: If you change the screen resistor from 1100 to 1400 ohm, the output power will decrease slightly, but the screen voltage will increase. This will make the EL34 tubes run hotter and may shorten their lifespan. The tone of the amplifier may also change, depending on how much the screen voltage affects the plate current and the distortion characteristics of the tubes. Some people may prefer a higher screen resistor value for a smoother and more compressed sound, while others may like a lower value for a more dynamic and punchy sound. It is a matter of personal preference and experimentation.
@@LexJones Here's what the google AI has to say: If you change the screen resistor from 1100 to 1400 ohms, the output power of the amplifier will decrease. This is because the screen resistor controls the current flow to the screen grid of the EL34 tube, and a higher resistance will result in a lower current flow. This will reduce the power dissipation in the tube, but it will also reduce the output power.
The amount of change in output power will depend on the specific amplifier and the amount by which the screen resistor is increased. However, in general, increasing the screen resistor will reduce the output power by about 20%.
In addition to the change in output power, increasing the screen resistor can also affect the sound of the amplifier. A higher screen resistor will typically result in a darker, warmer sound with less high-end sparkle. This is because the screen resistor affects the bias point of the tube, and a higher screen resistor will result in a more biased tube.