curious , since randall has one in the lineup and the Vx module certainly would benefit from the el84 as would the Marshall voiced mods a mod 20 head would be awesome . and if it was a 2 module .that would rule
MOD 20 ..what do you think
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guitarguy510
Well-known member
You can actually throw a set of THD Yellowjacks in the power amp section of the MOD50 head/combo and bias the amp for EL-84s that way and theorhetically that will allow you to run you amp @ about 20 watts with the EL-84 sound you are looking for! 
Just make sure you bias it correctly, Frank/Bruce can explain it to you if needed. There you have it... an instant "MOD20" AND it has two slots for modules! Problem solved! :lol: Hope that helps!
Just make sure you bias it correctly, Frank/Bruce can explain it to you if needed. There you have it... an instant "MOD20" AND it has two slots for modules! Problem solved! :lol: Hope that helps!MetalMajik
Well-known member
If what I've read is correct, no bias adjustment is necessary with the yellow jackets as they turn the tubes into "Cathode Bias" tubes. I'm sure someone with more technical expertise can explain cathode bias, but i think it means self bias
guitarguy510
Well-known member
FINE! I'll make it easy and just show you! This is exactly what the Egnater Manual states:
"Power Tube Bias:
What is bias? Simply put, it is a circuit inside the power amplifier section that controls the ?idle current? that flows through the power tubes. Much like the idle speed on a car. There is an optimum setting where the engine (amplifier) is running (idling) fast (hot) enough to keep it from stalling (distorting) but not too fast (hot) to cause excessive wear and overheating. Get it?
Why don?t all amplifiers have bias or idle current adjustments?
Most do have some provision for that but typically involve removing the amp chassis from the box, exposing you to very dangerous high voltage. Special test equipment and knowledge of amp circuits and tubes is also needed. Not a skill most musicians possess and shouldn?t need to.
Why would I want to adjust the bias?
All power tubes are different. They each have unique sonic and electrical characteristics. The MOD50 amplifier is designed to accept a variety of different tube types. EL34, 6L6, 5881, 6CA7 and 6550 are among the possible choices. Because they are all different, each requires different bias settings for safety, reliability and optimum performance.
Please read the following instructions on how to use this cool feature??.
You will need a decent quality digital voltmeter capable of measuring in the 100 to 200 millivolts DC range. This is a very basic type of meter available at any electronic supply house or Radio Shack. They typically cost anywhere from $10 to $25, about the cost of one bias adjustment from your local amp tech.
You will also need a small, flat blade screwdriver to turn the adjustment control that is recessed inside the grommet on the rear panel.
Turn the amp on, standby switch in the HIGH POWER position. All controls all the way down. Turn the meter on and set for reading DC millivolts. Consult the meter instructions for how to do this properly. Since all meters are different it is extremely important that you thoroughly understand what you are looking at on the meter display.
Insert the black (negative) test lead into the panel hole labeled COMMON.
Each tube has its own fuse, tube failure indicator and test point.
First step is to insert the red (positive) meter lead into the TUBE 1 test point hole.
With your flat blade screwdriver, turn the BIAS ADJUST control to obtain a correct reading from the chart below. Write down the reading. NOTE: The bias adjustment control is active ONLY in the HIGH POWER mode.
Now move the red meter lead to the other testpoint. The reading should be within +/- 3mVDC of the reading from the previous tube. This would be considered a matched pair. If you find a difference in readings of more than 4mVDC between the two, this would be an indication that the tubes may not be closely matched. This is not a confirmation of defective tubes and is not a cause for alarm. Rather it is simply that the tubes may not be perfectly matched and, consequently, you may not achieve maximum performance.
RECOMMENDED BIAS SETTINGS
6L6/5881 28mV to 35mV
EL34/6CA7 32mV to 40mV
E34L/E34Ls 35mV to 42mV
6550 35mV to 45mV
6V6 (JJ ONLY !!!!!!!!!!!) 18mV to 22mV
Displays differ from one meter to the next. Some may indicate, for example, 30.0 for 30 millivolts. Others may show .030 for 30 millivolts. Knowing how your meter works if of the utmost importance.
You should always check the bias readings whenever you replace output tubes and readjust if needed. Since we?ve made it so simple, there is no reason to not do it. "
That explains it the best!
"Power Tube Bias:
What is bias? Simply put, it is a circuit inside the power amplifier section that controls the ?idle current? that flows through the power tubes. Much like the idle speed on a car. There is an optimum setting where the engine (amplifier) is running (idling) fast (hot) enough to keep it from stalling (distorting) but not too fast (hot) to cause excessive wear and overheating. Get it?
Why don?t all amplifiers have bias or idle current adjustments?
Most do have some provision for that but typically involve removing the amp chassis from the box, exposing you to very dangerous high voltage. Special test equipment and knowledge of amp circuits and tubes is also needed. Not a skill most musicians possess and shouldn?t need to.
Why would I want to adjust the bias?
All power tubes are different. They each have unique sonic and electrical characteristics. The MOD50 amplifier is designed to accept a variety of different tube types. EL34, 6L6, 5881, 6CA7 and 6550 are among the possible choices. Because they are all different, each requires different bias settings for safety, reliability and optimum performance.
Please read the following instructions on how to use this cool feature??.
You will need a decent quality digital voltmeter capable of measuring in the 100 to 200 millivolts DC range. This is a very basic type of meter available at any electronic supply house or Radio Shack. They typically cost anywhere from $10 to $25, about the cost of one bias adjustment from your local amp tech.
You will also need a small, flat blade screwdriver to turn the adjustment control that is recessed inside the grommet on the rear panel.
Turn the amp on, standby switch in the HIGH POWER position. All controls all the way down. Turn the meter on and set for reading DC millivolts. Consult the meter instructions for how to do this properly. Since all meters are different it is extremely important that you thoroughly understand what you are looking at on the meter display.
Insert the black (negative) test lead into the panel hole labeled COMMON.
Each tube has its own fuse, tube failure indicator and test point.
First step is to insert the red (positive) meter lead into the TUBE 1 test point hole.
With your flat blade screwdriver, turn the BIAS ADJUST control to obtain a correct reading from the chart below. Write down the reading. NOTE: The bias adjustment control is active ONLY in the HIGH POWER mode.
Now move the red meter lead to the other testpoint. The reading should be within +/- 3mVDC of the reading from the previous tube. This would be considered a matched pair. If you find a difference in readings of more than 4mVDC between the two, this would be an indication that the tubes may not be closely matched. This is not a confirmation of defective tubes and is not a cause for alarm. Rather it is simply that the tubes may not be perfectly matched and, consequently, you may not achieve maximum performance.
RECOMMENDED BIAS SETTINGS
6L6/5881 28mV to 35mV
EL34/6CA7 32mV to 40mV
E34L/E34Ls 35mV to 42mV
6550 35mV to 45mV
6V6 (JJ ONLY !!!!!!!!!!!) 18mV to 22mV
Displays differ from one meter to the next. Some may indicate, for example, 30.0 for 30 millivolts. Others may show .030 for 30 millivolts. Knowing how your meter works if of the utmost importance.
You should always check the bias readings whenever you replace output tubes and readjust if needed. Since we?ve made it so simple, there is no reason to not do it. "
That explains it the best!
guitarguy510
Well-known member
guitarguy510 said:I'll make it easy and just show you! This is exactly what the Egnater Manual states:
"Power Tube Bias:
What is bias? Simply put, it is a circuit inside the power amplifier section that controls the ?idle current? that flows through the power tubes. Much like the idle speed on a car. There is an optimum setting where the engine (amplifier) is running (idling) fast (hot) enough to keep it from stalling (distorting) but not too fast (hot) to cause excessive wear and overheating. Get it?
Why don?t all amplifiers have bias or idle current adjustments?
Most do have some provision for that but typically involve removing the amp chassis from the box, exposing you to very dangerous high voltage. Special test equipment and knowledge of amp circuits and tubes is also needed. Not a skill most musicians possess and shouldn?t need to.
Why would I want to adjust the bias?
All power tubes are different. They each have unique sonic and electrical characteristics. The MOD50 amplifier is designed to accept a variety of different tube types. EL34, 6L6, 5881, 6CA7 and 6550 are among the possible choices. Because they are all different, each requires different bias settings for safety, reliability and optimum performance.
Please read the following instructions on how to use this cool feature??.
You will need a decent quality digital voltmeter capable of measuring in the 100 to 200 millivolts DC range. This is a very basic type of meter available at any electronic supply house or Radio Shack. They typically cost anywhere from $10 to $25, about the cost of one bias adjustment from your local amp tech.
You will also need a small, flat blade screwdriver to turn the adjustment control that is recessed inside the grommet on the rear panel.
Turn the amp on, standby switch in the HIGH POWER position. All controls all the way down. Turn the meter on and set for reading DC millivolts. Consult the meter instructions for how to do this properly. Since all meters are different it is extremely important that you thoroughly understand what you are looking at on the meter display.
Insert the black (negative) test lead into the panel hole labeled COMMON.
Each tube has its own fuse, tube failure indicator and test point.
First step is to insert the red (positive) meter lead into the TUBE 1 test point hole.
With your flat blade screwdriver, turn the BIAS ADJUST control to obtain a correct reading from the chart below. Write down the reading. NOTE: The bias adjustment control is active ONLY in the HIGH POWER mode.
Now move the red meter lead to the other testpoint. The reading should be within +/- 3mVDC of the reading from the previous tube. This would be considered a matched pair. If you find a difference in readings of more than 4mVDC between the two, this would be an indication that the tubes may not be closely matched. This is not a confirmation of defective tubes and is not a cause for alarm. Rather it is simply that the tubes may not be perfectly matched and, consequently, you may not achieve maximum performance.
RECOMMENDED BIAS SETTINGS
6L6/5881 28mV to 35mV
EL34/6CA7 32mV to 40mV
E34L/E34Ls 35mV to 42mV
6550 35mV to 45mV
6V6 (JJ ONLY !!!!!!!!!!!) 18mV to 22mV
Displays differ from one meter to the next. Some may indicate, for example, 30.0 for 30 millivolts. Others may show .030 for 30 millivolts. Knowing how your meter works if of the utmost importance.
You should always check the bias readings whenever you replace output tubes and readjust if needed. Since we?ve made it so simple, there is no reason to not do it. "
That explains it the best!
Orren
Active member
MetalMajik said:
You are completely correct.
I have two Yellow Jacket Triodes in my MOD50, and no new bias was required, they self-bias.
BTW--the YJ Triodes basically operate at 1/2rds power of a normal EL84, so they bring the amp down to about 10W in full power mode, 2W in low power mode.
And they sound FANTASTIC! Smoother than a normal EL84, still chimey but without harshness, and tight lows.
Orren
