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25th September 2008, 01:05 AM  #1 
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Join Date: Mar 2008
Location: Austin, TX

EL34 UL Curves
Does anyone have or know where I can find EL34 43% ultralinear curves. Anode voltage will be around 300V. If nobody has them advice on how to draw them it will greatly be appreciated. Thanks in advance.

25th September 2008, 09:07 AM  #2 
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25th September 2008, 10:40 AM  #3  
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Those EL34 UL curves are for 43% screen tap and starting at 450V. The curves will be radically different with a 300V starting point, or with a different tap percentage. There are no low voltage UL curves published for that valve that I have found yet. I have spend considerable time looking too. Given a good enough set of curves( as in the g1=0 with variable g2 ), one can determine what the working envelope is( so to say the g1=0 upper grid line ). The rest is a bit of a guess unless you trace your own...and that is not trivial. On the load line, draw a 2k slope for 70 mA( assumed idle current ) in each direction from your starting point. The slope upwards and to the left will shift to 1k after that( as the other half of the OPT drops out of the picture when current ceases to flow ). Kinda simplistic, but that is a about what is happening. cheers, Douglas
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28th September 2008, 08:09 AM  #4 
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hello bandersnatch,
the TS asked for 43% UL curves, so no problem there... When you use a different percentage of the transformer winding for the 2nd grid, the curves will alter drastically. they do not change, when you take another Va. You can use this graph for a Va of 300,150 and even 450v .....the tube will not suddenly change it's parameters just by using a different anode voltage.... You might have to use another primary impedance for the transformer, as the loadline could get too steep but the curves will not change, provided g2 stays on the same percentage
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28th September 2008, 11:30 AM  #5  
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Look at the GE data for 6L6GC. That one is quite useful for determining the outer envelope of UL operation at various voltages. cheers, Douglas
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28th September 2008, 02:48 PM  #6  
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That's not what i'm telling you....we aren't talking about penthodes. When connecting a tube ultralinear there is feedback between g2 and anode. The rate of this feedback is determined by the ratio at which the ul tap is on the transformer winding. (that's why the Ul curves look like a crossbreed between penthode and triode) So, the ratio between anode/g2 determines the curves....this is a fixed ratio. within these set of curves you are free to pick the desired anode voltage that you want. when you pick 300V as anode voltage, the ratio between g2/anode will be the same as when you pick 450V as Va. hence, the steepnes of the curves will be the same.... [quote]Look at the GE data for 6L6GC. That one is quite useful for determining the outer envelope of UL operation at various voltages.[/uote] I'm not quite sure i understand what you mean by this... in this datasheet: http://www.mif.pg.gda.pl/homepages/f...93/6/6L6GC.pdf i haven't been able to find UL curves.... I find your point interesting, and hope we can get to a full understanding! best, Henk
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28th September 2008, 04:16 PM  #7  
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What do you think gets plugged into the socket? A UL tube? or a Pentode? Given that it is a pentode( or a beam tetrode, that is essentially a pentode ), the g2 voltage plays a critical role. It is no more complicated than that. The starting point is quite important, each set of curves starting from a differnet g2/anode level will be different. cheers, Douglas
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28th September 2008, 11:45 PM  #8 
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Thanks for the replies. I know for certain that g2 voltage has a large effect on UL curves just as it does in pentode mode. I made some basic measurements operating an EL34 with 300V to the plate in 43% UL mode and got results that do not come anywhere close to matching the 450V curves that are linked above. Andrew

29th September 2008, 11:54 AM  #9 
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Douglas,
I guess we're talking in different directions.... I've given it some thought and have to say i don't know what you mean by 'starting voltage'....could you please explain? (this would make sense when talking about penthodes) When i would have to plot an ul graph(keeping the sofia plot as example): i start at va=0, Ia=0 i connect a transformer to the anode, g2 on a winding tap, 43% from the anode. next i will give g1 5V and raise Va to 70V: my mA meter will read about 250mA next i will give g1 40V and raise Va to 490V my mA meter will read about 60mA so, why couldn't i use this graph with 300V??? that voltage has been used to plot the graph....it didn't change then.... If i had used 300V as 'starting voltage, i wouldn't have been able to plot g1@5V UL mode does not depend on a fixed g2 voltage (which is responsible for compressing/decompressing the curves in a penthode plot). if what you say is true, when playing music with a ul amplifier would mean constantly changing graph lines.... (because when g1 reaches 5V at the positive side of a signal va will be about 70V.....the curves will not change, because the ratio between anode and g2 will be the same (the winding hasn't suddenly altered to 22%)) best, henk
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