calculate +B in EL34 SE triode conect - diyAudio
 calculate +B in EL34 SE triode conect
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 27th October 2004, 01:30 PM #1 diyAudio Member   Join Date: Jun 2004 Location: bs.as. calculate +B in EL34 SE triode conect hello, I work in my project, one Single End EL34 in triode conection. I find in Philips manual EL34 operate in triode concention need in Vb.......375 V when design the power supply I must add to those 375V the volt drop in primari OPT and the difference to 0 the Vbias ? +B = 375v + Vdrop OPT + Vbias(positive sing) this is correct ??
 27th October 2004, 05:51 PM #2 diyAudio Member   Join Date: Jun 2002 Location: Denver, CO Plate supply voltage vs plate voltage I assume your circuit is cathode resistor bias and the el 34 is an output tube connected to the output transformer? Plate voltage is measured across the tube and does not include voltage drop across cathode resistor or anode load whatever. Plate supply voltage is measured across the plate load to ground............I think. Anybody else want to help him (me)? Just a guess here but Vb at 375 for el 34 is probably referring to plate voltage and does not include cathode resistor voltage drop. Add voltage drop across output transformer and cathode resistor to 375 (plate voltage) to get B+ or plate supply voltage.
 29th October 2004, 05:27 AM #3 diyAudio Moderator Emeritus     Join Date: Jan 2004 Location: Jakarta In the Gospel according to Mullard, the SE triode-connected EL34 requires 250v plate-to-cathode, with -15v on the grid. Quiescent current is given as 70mA, so the cathode bias resistor should be 214 ohms. Assuming 5v drop across the OPT primary, your total B+ would need to be 250+15+5v = 270v.
diyAudio Member

Join Date: Jan 2002
Re: Plate supply voltage vs plate voltage

Quote:
 Originally posted by alejo hello, I work in my project, one Single End EL34 in triode conection. I find in Philips manual EL34 operate in triode concention need in Vb.......375 V when design the power supply I must add to those 375V the volt drop in primari OPT and the difference to 0 the Vbias ? +B = 375v + Vdrop OPT + Vbias(positive sing) this is correct ??
Now this can be a bit tricky depending on which manual you look at. I always assume that B+ refers to the supply rail and Vb the voltage measured at the plate. Unless it specifically states otherwise, then you can assume that the cathode of the tube under test is grounded, and the bias voltage applied to the grid.

So based on what you've said, B+ would be 375V plus the drop across the OPT primary. Either way it's not going to make a massive difference to the distortion or output power. If you want it cathode biassed, you'll need to add the drop across the cathode resistor too.

diyAudio Member

Join Date: Jul 2004
Location: Melbourne, Victoria
EL34SE

I don't have a Philips manual so I can't comment on the operating point suggested. However, I have attached a copy of the EL34 triode curves with a 5K loadline (i.e. for an OPT with primary impedance 5K). Assuming idle plate voltage of 375V, the grid would be need to be 32V more negative than the cathode to set bias and keep within max plate dissipation at idle. This means 32V has to be dropped acrossed the cathode resistor (bypassed by suitably sized capacitor). The idle current at this point is about 67mA, so R = V/I = 32/0.067 = 477.6 ohm. This is the cathode resistor value. The DC drop over the OPT primary also has to be considered, for something like the Hammond 125ESE this is about 90 ohm so V = IR = 0.067*90 = 6V. The B+ has to provide all this DC voltage (i.e. across the cathode resistor, the EL34 and DC drop arcross OPT primary) so B+ = 32+375+6 = 413V.

Also, since the grid sits at -32V, for full output power (in class A1), the driver stage has to swing 64V peak to peak.

I have assumed cathode bias. Also, I have not checked the operating point for sensibilities (apart from plate dissipation - which is about maximum) - it's really just an example

The EL34 triode curves were from Audiomatica's website
Attached Images
 el34.jpg (61.9 KB, 507 views)

diyAudio Member

Join Date: Jan 2002
Re: EL34SE

Quote:
 Originally posted by audiousername I don't have a Philips manual so I can't comment on the operating point suggested. However, I have attached a copy of the EL34 triode curves with a 5K loadline (i.e. for an OPT with primary impedance 5K). Assuming idle plate voltage of 375V, the grid would be need to be 32V more negative than the cathode to set bias and keep within max plate dissipation at idle. This means 32V has to be dropped acrossed the cathode resistor (bypassed by suitably sized capacitor). The idle current at this point is about 67mA, so R = V/I = 32/0.067 = 477.6 ohm. This is the cathode resistor value. The DC drop over the OPT primary also has to be considered, for something like the Hammond 125ESE this is about 90 ohm so V = IR = 0.067*90 = 6V. The B+ has to provide all this DC voltage (i.e. across the cathode resistor, the EL34 and DC drop arcross OPT primary) so B+ = 32+375+6 = 413V. Also, since the grid sits at -32V, for full output power (in class A1), the driver stage has to swing 64V peak to peak. I have assumed cathode bias. Also, I have not checked the operating point for sensibilities (apart from plate dissipation - which is about maximum) - it's really just an example The EL34 triode curves were from Audiomatica's website
alejo: all the above is a good example of how to calculate it all out, but I wouldn't exceed a plate dissipation above about 80% if you want some life from the tube.

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Join Date: Jul 2004
Location: Melbourne, Victoria
Re: Re: EL34SE

Quote:
 Originally posted by Brett alejo: all the above is a good example of how to calculate it all out, but I wouldn't exceed a plate dissipation above about 80% if you want some life from the tube.

True... that was just an example. I haven't even calculated the output power. All depends on how much the valves cost I suppose.

 29th October 2004, 12:21 PM #8 diyAudio Member   Join Date: Jun 2004 Location: bs.as. Thank you very much to all, I am going to experiment with 375V and 413V in the +B supply to see that differences I obtain. Alejo.
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Join Date: Jan 2002
Quote:
 Originally posted by alejo Thank you very much to all, I am going to experiment with 375V and 413V in the +B supply to see that differences I obtain. Alejo.
If you use 413V B+ with audiousername's numbers, you'll quickly cook the tube.

I ran a couple of similar setups quickly in SEAmp CAD and came up with;

B+ = 375V
Ia = 67mA
Rk = 420 ohm
Vg = -28V
Pa = 21.4W or 76%
Pout = 3.7Wrms

B+ = 415V
Ia = 62mA
Rk = 530 ohm
Vg = -33V
Pa = 22.2W or 79%
Pout = 4.76Wrms

Both assume a 5k load and about 450 ohms of primary resistance.

 29th October 2004, 01:17 PM #10 diyAudio Member   Join Date: Jun 2004 Location: bs.as. Brett, I want buil this amp with One Electron Transformer UBT-3 Specifications: Primary impedance: 3000 Ohms Primary resistance: 286ohms nominal what say your "SEAmp CAD" if I use: B+ = 375 V Rk = 370 Ohms I want to obtain 6 Wrms in loudspeaker with EL34 as triode and 3000ohms. thanks alejo

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