Francois, i'll certainly do that.
R113 - 117 Left Channel
R213 - 217 Right Channel
Might you please explain 'multiple that with the voltage from the screen to the top of cathode' ?
R113 - 117 Left Channel
R213 - 217 Right Channel
Might you please explain 'multiple that with the voltage from the screen to the top of cathode' ?
It is similar to the total tube dissipation calculation that you have done before, where you multiply the current through the cathode resistor (which is the same as the current through the tube) by the voltage across the tube. In this case you want to check only the screen grid dissipation, so you calculate the current through the 100R resistors (113&117, 213&217) and multiply that by the voltage across the screen grid to get the screen dissipation. The voltage across the screen is measured from pin 9 to pin 3.
My CL80 has arrived! Will connect it in series with the Live A.C. going to mains Tx.
Doing some work on a small piece of veroboard & chassis, wiring etc. to mount the two 5W resistors.
Screen grid dissipation left to measure.
Calculate the current through the 100R's R113, 117 (left ch.) and R 213, 217 (right ch.) ?
Francois G, would you be kind enough to explain this a little easier?
Doing some work on a small piece of veroboard & chassis, wiring etc. to mount the two 5W resistors.
Screen grid dissipation left to measure.
Calculate the current through the 100R's R113, 117 (left ch.) and R 213, 217 (right ch.) ?
Francois G, would you be kind enough to explain this a little easier?
Checking the screen dissipation is something I routinely do. In your case it is not essential because you are not running the EL84 hard (anymore!)
If you choose to do it be careful because you are measuring at high voltage potential - best done with mini grabber test leads for your multimeter in one hand and the other hand behind your back (safety precaution!). To calculate the screen current you need to measure the difference in voltage across the 100R resistors and then calculate I=v/100. The current I is then multiplied by the voltage across the screen grid to arrive at the screen dissipation. The voltage across the screen grid is measured from pin 9 to pin 3 for each EL84. Hope this is clearer.
If you choose to do it be careful because you are measuring at high voltage potential - best done with mini grabber test leads for your multimeter in one hand and the other hand behind your back (safety precaution!). To calculate the screen current you need to measure the difference in voltage across the 100R resistors and then calculate I=v/100. The current I is then multiplied by the voltage across the screen grid to arrive at the screen dissipation. The voltage across the screen grid is measured from pin 9 to pin 3 for each EL84. Hope this is clearer.
Finally, i have managed to do some measurements.
With thanks to Francois i have managed to carry some checks.
I have now fitted the Current Limiter CL80.
300 - 0 - 300 = 604v
B+ = 315v
8.8R loads
Cathodes: -
V102 = 10.8v
V101 = 10.6v
V202 = 10.6v
V201 = 10.9V
Dissipation calculations: -
V102 - 0.49V ÷ 100R = 0.0049A - 4.9mA
303v x 0.0049 = 1.48 watts
V101, V201, V202 to be checked tomorrow.
By the way does anyone knows what is the recommended audio level input?
With thanks to Francois i have managed to carry some checks.
I have now fitted the Current Limiter CL80.
300 - 0 - 300 = 604v
B+ = 315v
8.8R loads
Cathodes: -
V102 = 10.8v
V101 = 10.6v
V202 = 10.6v
V201 = 10.9V
Dissipation calculations: -
V102 - 0.49V ÷ 100R = 0.0049A - 4.9mA
303v x 0.0049 = 1.48 watts
V101, V201, V202 to be checked tomorrow.
By the way does anyone knows what is the recommended audio level input?
Ok, just finished checking the other valves.
V101 = 1.43 watts
V202 = 1.43 watts
V201 = 1.40 watts
V101 = 1.43 watts
V202 = 1.43 watts
V201 = 1.40 watts
By the way does anyone knows what is the recommended audio level input?
What is the actual output in watts of the amp?
What is the actual output in watts of the amp?
Wait a sec.....
B+ = 315v
8.8R loads
Cathodes: -
V102 = 10.8v
V101 = 10.6v
V202 = 10.6v
V201 = 10.9V
V101, for example, is one of the EL84s, correct? Its cathode resistor is somewhere between 270 and 300 ohms, correct?
Let's assume 285 ohms for argument sake. 10.6 volts divide by 285 = 0.037 amps (37 milliamps).
B+ = 315 volts, let's assume 310 on the plates minus 10.6 on the cathode = 299.4 volts.
299.4 x 0.037 amps = 11.1 watts. Not 1.43 watts.
Anyway, a dissipation of 11 watts is fine. It could be a bit higher, 12 to 13 without causing distress, but I wouldn't go lower than 11 watts. Run the calculation with the real resistor and the actual plate voltage for a more accurate result.
S.
B+ = 315v
8.8R loads
Cathodes: -
V102 = 10.8v
V101 = 10.6v
V202 = 10.6v
V201 = 10.9V
V101, for example, is one of the EL84s, correct? Its cathode resistor is somewhere between 270 and 300 ohms, correct?
Let's assume 285 ohms for argument sake. 10.6 volts divide by 285 = 0.037 amps (37 milliamps).
B+ = 315 volts, let's assume 310 on the plates minus 10.6 on the cathode = 299.4 volts.
299.4 x 0.037 amps = 11.1 watts. Not 1.43 watts.
Anyway, a dissipation of 11 watts is fine. It could be a bit higher, 12 to 13 without causing distress, but I wouldn't go lower than 11 watts. Run the calculation with the real resistor and the actual plate voltage for a more accurate result.
S.
Oops, guess I wasn't following closely enough.
It's typically not necessary getting into the weeds so much considering screen grid dissipation separately. At least not with common output tubes, EL84, EL34, KT88 etc. Generally considering the combined anode and screen grid dissipation together works well.
S.
It's typically not necessary getting into the weeds so much considering screen grid dissipation separately. At least not with common output tubes, EL84, EL34, KT88 etc. Generally considering the combined anode and screen grid dissipation together works well.
S.
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Hi Steve, I routinely check screen grid dissipation for all my amplifiers. Granted I build more with high-perveance tubes than the common ones. But if you have a screen grid resistor why not? Especially if you are running in UL at higher than normal voltages, as the OP dealt with initially.
The SSP PCB is also used for EL86 amplifiers with Pg2 max =1.75 watt it is essential to monitor screen grid dissipation, and 6P15P (as I do) with Pg2 max = 1.5 watt
Do you perhaps have an answer for @calpe? I thought with you experimentation you perhaps made note of these parameters.
The SSP PCB is also used for EL86 amplifiers with Pg2 max =1.75 watt it is essential to monitor screen grid dissipation, and 6P15P (as I do) with Pg2 max = 1.5 watt
Do you perhaps have an answer for @calpe? I thought with you experimentation you perhaps made note of these parameters.
The simulation of LTspice results in the following values:
Output power of 14 watts into 8 ohms and 17 watts into 4 ohms,
each with an input voltage of 1 Vpp (peak to peak).
Strong distortions are generated above 1 Vpp.
LTspice file
Output power of 14 watts into 8 ohms and 17 watts into 4 ohms,
each with an input voltage of 1 Vpp (peak to peak).
Strong distortions are generated above 1 Vpp.
LTspice file
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Thanks Steve for your reply and also to the others.
Yes my B+ is 315v and Cathode resistors are 300R
Would i be correct in saying that: -
So e.g. 10.6v ÷ 315v = 0.0337 amps (34mA)
Grids (Av. 304v) 304v X 0.034 = 10.336 Watts
Would love to know the min.-max. input signal level, if anyone knows 😉
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Ive now decided to fit a small (quiet) A.C. fan.
Having fitted two parallel resistors for R1 (150R + 560R = 122R) being 5W's and the 3W resistors mounted on the PCB and mounted under the top plate of the chassis, i'd rather things ran a bit cooler.
Goes against the etiquette of a Valve amplifier build, but as it wont be seen and hardly heard, what the hell.
My choice.
Having fitted two parallel resistors for R1 (150R + 560R = 122R) being 5W's and the 3W resistors mounted on the PCB and mounted under the top plate of the chassis, i'd rather things ran a bit cooler.
Goes against the etiquette of a Valve amplifier build, but as it wont be seen and hardly heard, what the hell.
My choice.
How many watts is the composite 122R resistor actually dissipating? If there are some holes in your top plate I would not have expected a need for a fan. Could you drill more holes in the top plate?