kgrlee,
40mA cathode current on each EL34 is called a Class B amp?
40mA x 470V = 18.8 Watts dissipation.
I thought push pull Class B was supposed to be the most efficient amplifier mode by far.
All definitions over time change for the better?
40mA cathode current on each EL34 is called a Class B amp?
40mA x 470V = 18.8 Watts dissipation.
I thought push pull Class B was supposed to be the most efficient amplifier mode by far.
All definitions over time change for the better?
It claims 40W / channel 8R so it's Class AB but waving my Jurassic valve finger in the air, probably more B than A ... certainly by HiFi EL34 standards. 🙂
Anyone got a reliable schematic?
Anyone got a reliable schematic?
kgrlee,
1. RCA's "Transmitting Tubes", technical manual TT-5, Page 15 gives a good description of Class B, and Class A, Class AB, and Class C.
The intent of Class B is not met when Push Pull EL34 tubes each have 40mA of cathode current.
Class AB is met.
You can say something is more Class B or more Class A; But that misses the point of True AB, True B, and True A Classes.
2. For a different reference, check out the RCA "Receiving Tube Manual", Technical Series RC-18:
Page 331 schematic for a Class AB1 6V6 10 Watt push pull amplifier.
Calculate the quiescent cathode current if you wish.
Page 332 schematic for a Class AB1 6L6G 25 Watt push pull amplifier.
Calculate the quiescent cathode current if you wish.
Page 333 schematic for a Class B 6N7 10 Watt push pull amplifier for power saving Mobile service.
Calculate the quiescent cathode current if you wish.
3. Newbies take note, marketing does not always tell the truth.
A Class A restaurant is one thing. Quality.
A Class A amplifier is another (Quality can be anything from truly Rotten Class A; to next to Perfect Class A).
Do not confuse the two meanings of Class A.
1. RCA's "Transmitting Tubes", technical manual TT-5, Page 15 gives a good description of Class B, and Class A, Class AB, and Class C.
The intent of Class B is not met when Push Pull EL34 tubes each have 40mA of cathode current.
Class AB is met.
You can say something is more Class B or more Class A; But that misses the point of True AB, True B, and True A Classes.
2. For a different reference, check out the RCA "Receiving Tube Manual", Technical Series RC-18:
Page 331 schematic for a Class AB1 6V6 10 Watt push pull amplifier.
Calculate the quiescent cathode current if you wish.
Page 332 schematic for a Class AB1 6L6G 25 Watt push pull amplifier.
Calculate the quiescent cathode current if you wish.
Page 333 schematic for a Class B 6N7 10 Watt push pull amplifier for power saving Mobile service.
Calculate the quiescent cathode current if you wish.
3. Newbies take note, marketing does not always tell the truth.
A Class A restaurant is one thing. Quality.
A Class A amplifier is another (Quality can be anything from truly Rotten Class A; to next to Perfect Class A).
Do not confuse the two meanings of Class A.
Regarding how much power this resistor will see given the posted circuit without faults.
I ran a simple simulation which shows the peak current in the resistor with the amp running at maximum power (defined as the voltage from grid to plate of the EL34=0 volts) sign wave, and an 8 Ohm load on the 8 Ohm tap, to be about .35A. The resistor power is then 1.2 watts peak, and about 1/4 that value for its one cycle AC average or 0.3 Watts.
This is pushing it for a 1-Watt resistor if the amp is continuously outputting its full power. If the amp is used in that way or sees low Z loads. a beefier resistor might be in order. Possibly a 5-Watt resistor.
I ran a simple simulation which shows the peak current in the resistor with the amp running at maximum power (defined as the voltage from grid to plate of the EL34=0 volts) sign wave, and an 8 Ohm load on the 8 Ohm tap, to be about .35A. The resistor power is then 1.2 watts peak, and about 1/4 that value for its one cycle AC average or 0.3 Watts.
This is pushing it for a 1-Watt resistor if the amp is continuously outputting its full power. If the amp is used in that way or sees low Z loads. a beefier resistor might be in order. Possibly a 5-Watt resistor.
Plate voltage ~ 470V; Cathode current ~ 350 mA -> EL34 Pd = 165 Watts peak, your average dissipation >40 watt. Wow! Maybe the EL34 is already caput.
a class A amp will have the same power draw at idle and when delivering full power, you can see this when using a power monitor, a class AB will have a class A window if a few watts, braking out into class B when the class A window is exceeded...
both class B and class AB should not have notch distortion...
by default, B and AB are B1 and AB1, only with grid current does it become B2 and AB2..
so your Anthem is AB1...
both class B and class AB should not have notch distortion...
by default, B and AB are B1 and AB1, only with grid current does it become B2 and AB2..
so your Anthem is AB1...
Well when it’s pulling 0.35A, the plate and screen are more like 100, and 350 volts respectively. I would have to go back to the sym for the actual numbers. Yea, the tube is getting pounded.
your Anthem amp is just another implementation of the Mullard 5-20 concept/topology...i like this topology...
350ma/4 = 85ma per plate, that is 30 watts plate for a 24watt rated tube, any signs of red plating?
It’s a sym set up to show max peak expected current. The only red plate is the one next to my monitor with spaghetti on it!
Resistors heat up according to the integrated power, I'squared x R over time.
Different resistors respond differently to extremely short time, extremely high current overloads.
Choose your current monitoring sense resistor wisely.
But if the original designer intended that resistor to also be a fuse, then override his decision if you wish . . . in that case use a 10 Watt wirewound . . .
But please do not send the amplifier to me to repair it next time.
Replace the EL34, replace the output transformer, or whatever blows out with the overrated cathode resistor.
Just my opinion
Different resistors respond differently to extremely short time, extremely high current overloads.
Choose your current monitoring sense resistor wisely.
But if the original designer intended that resistor to also be a fuse, then override his decision if you wish . . . in that case use a 10 Watt wirewound . . .
But please do not send the amplifier to me to repair it next time.
Replace the EL34, replace the output transformer, or whatever blows out with the overrated cathode resistor.
Just my opinion
Potentiallyincorrect,
I agree.
All those things you have mentioned, are also listed several times in the 58 posts of this thread.
DeJaVu all over again.
Perhaps nothing yet has been checked, re-soldered, or replaced to fix the problem.
It is going to occur again in that channel.
Doing the same thing over and over again, but expecting a different outcome is the definition of insanity.
I agree.
All those things you have mentioned, are also listed several times in the 58 posts of this thread.
DeJaVu all over again.
Perhaps nothing yet has been checked, re-soldered, or replaced to fix the problem.
It is going to occur again in that channel.
Doing the same thing over and over again, but expecting a different outcome is the definition of insanity.
I completely believe this line of thought. Which one would be most likely to happen once every several years?
At this point my plan is to replace the resistor and hope for the best. Which is the definition of insanity, I agree.
But checking the other things are out of my skill set, and if/when I bring the amp back to a tech, I want to have as much knowledge of the other possibilities as possible.
If you can replace a resistor, you can replace a capacitor. This assumes you can do good soldering work.
We can give detailed help to add the safety resistors so that is also within your capabilities.
Cleaning a socket and inspecting joints does not take much skill either.
I also understand if you don’t want to do it for a host of reasons, good luck.
We can give detailed help to add the safety resistors so that is also within your capabilities.
Cleaning a socket and inspecting joints does not take much skill either.
I also understand if you don’t want to do it for a host of reasons, good luck.