Hi All,
I'm doing development of my new push pull class A EL34 amp. I am currently working on the design of the input part. (Pic_1). +HT is 440V from regulated supply, 30 seconds delayed after heating. Operating point you can see on pic_2.
My question: is 440V HT safety for E88CC?
When i look in datasheet there is two maximum Va values (Pic_3). First and second row.
Which is important for me? I always thought that Vao is the value at start-up, or the value when Ia=0. Then what is the second row in the datasheet for?
Thank you
Jan
I'm doing development of my new push pull class A EL34 amp. I am currently working on the design of the input part. (Pic_1). +HT is 440V from regulated supply, 30 seconds delayed after heating. Operating point you can see on pic_2.
My question: is 440V HT safety for E88CC?
When i look in datasheet there is two maximum Va values (Pic_3). First and second row.
Which is important for me? I always thought that Vao is the value at start-up, or the value when Ia=0. Then what is the second row in the datasheet for?
Thank you
Jan
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On my Philips datasheet, the first value (550V) is specified as "cold", meaning with filament turned off.
I believe that the second value (400V) is the maximum value with filament turned on, but no current.
You probably need to lower your anode voltage supply.
I believe that the second value (400V) is the maximum value with filament turned on, but no current.
You probably need to lower your anode voltage supply.
In the Philips E88CC datasheet (1968-2000) the Ua (anode-cathode voltage, NOT HT!) limit is 220V (at max. anode dissipation 1.5W) or 250V at 0.8W dissipation.
You operating point (169.6V) is in the safe area, enough far from the limit value, and dissipating (0.6784W/half tube, 1.3568W/tube) too (as you can see in Pic_2 loadline too).
You operating point (169.6V) is in the safe area, enough far from the limit value, and dissipating (0.6784W/half tube, 1.3568W/tube) too (as you can see in Pic_2 loadline too).
I think the question is what the maximum voltage is when the heater is cold.
Cold heater: 550V
Warm heater, no cathode current due to negative grid: 400V.
I don't think your circuit will experience the second case, you should be fine.
Cold heater: 550V
Warm heater, no cathode current due to negative grid: 400V.
I don't think your circuit will experience the second case, you should be fine.
I use a HT regulator, so 440V. But i have 30s delayed the HT after Power ON. I also think that under normal circumstances I should not reach 440V at Ia=0. Pic_2 shows the expected voltage fluctuation at the output for maximal amp power. But if there is too much AC voltage at the input, it is theoretically possible. Nevertheless, exceeding the maximum voltage 400V by 40V is not critical (only 10% more), I think. What do you say?
The 400V datasheet value is listed according to the "design center" system, so at 440V you are exactly at the absolute maximum value allowed. A ideal E88CC should work fine. A real one maybe not. Dropping the supply voltage is trivial. You can build the amplifier, measure the actual anode to cathode voltage, and lower it if needed. I also believe that in normal conditions the E88CC will never experience the full 440V supply voltage, so this is only a precaution should abnormal condition arise.
My 6922 preamp starts working after 8 seconds.
It has about 60 of the 125v B+ at this point.
It will be ready after 30 seconds unless the heater fails.
It has about 60 of the 125v B+ at this point.
It will be ready after 30 seconds unless the heater fails.
Thanks for the replies guys.
At first I wanted to minimize the number of components. But now I'll lower the HT just to be sure. This will make sure I never get too high with Ua. I will also reduce the power dissipation of Ra.
At first I wanted to minimize the number of components. But now I'll lower the HT just to be sure. This will make sure I never get too high with Ua. I will also reduce the power dissipation of Ra.
BTW what's the goal of desired output swing?
The stage gain about 28-29dB.
If the input is 2VRMS (2.828Vp) the output swing peek is 79.7V.
The stage gain about 28-29dB.
If the input is 2VRMS (2.828Vp) the output swing peek is 79.7V.
I need 20Vp for driving one EL34 open loop (class A PP UL). With nfb i need 40Vp.
My amplifier will be a monoblock with input sensitivity approximately 1Vrms unbalanced or 2Vrms balanced.
My amplifier will be a monoblock with input sensitivity approximately 1Vrms unbalanced or 2Vrms balanced.
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So, if the input is 1V RMS (1.414V peek) and desired output peek is 40V, the required gain is 28x, the 29dB is perfect.
BTW I prefer higher anode current (4mA is in the curved part of characteristic) and lower anode voltage operating points for E88CC.
BTW I prefer higher anode current (4mA is in the curved part of characteristic) and lower anode voltage operating points for E88CC.
You are right about the operating point. But with differential pair, the nonlinearity should be partly compensated. Or am I wrong? I chose the current operating point due to the limitations of the LM334. In the simulations, the harmonic distortions came out perfectly. Of course I have to build it and take measurements.
Very nice my friend. Yes, I am considering the use of trimmers in anodes and cathodes. But that's only with a real circuit and a real measurement. What do you think the distortion values would be at my operating point? It is a question of how the IMD distortion will be done - but this i see only in real measurements.
At your operating point (4mA, 170V), at 68k load the distortion is enough low ... if the output swing not too high.
At 40Vp (80Vpp) the distortion about double, than higher current (10mA), lower Ua (140V), 30k load version.
But ..these are simulations .. and simulation as correct as the mathematical models .. the real measurement is the fact.
At 40Vp (80Vpp) the distortion about double, than higher current (10mA), lower Ua (140V), 30k load version.
But ..these are simulations .. and simulation as correct as the mathematical models .. the real measurement is the fact.
