6L6 pp triode mode

[Cannibal]

Hello everybody,

I'm working on an homebrew design where i would like to try triode connection and class 2 but i'm having trouble in finding a datasheet that provides the curves of a triode strapped 6L6 at quite high voltages.

The amp will have a quad of triode strapped 6L6 in class AB2 fixed bias working at 450v on the plates; the output and power transformer are salvaged from a marshall MA100 and the OT has a primary impedance of 1,7k. When i try to design the load lines, the class B line is so steep that it gets out of the drawing before the 0V point on the x-axis. Is it safe to do something like this? I'm not at home right now, as soon as i come home i will attach my load lines. Thank you everybody.

[Zozobra]

More often than not, I've had to extend the y-axis (Ia) by a few hundred milliamps when drawing loadlines. The key thing to be mindful of is the max plate dissipation. The class B loadline can cross this and it will be okay. Most loadlines of commercial amps will exceed 1xWa without issue. You will get into trouble if you exceed 2xWa in a pushpull amp. I draw this on if my loadlines dissipation looks sketchy.

How will you be driving the grid positive?

[Cannibal]

Here's the load line (my photoshop skills are very basic but I think that this one could be at least readable). In red there's the max dissipation curve, in blue the class A operation and Yellow is class AB.

I'm driving it with a couple of mosfet, the design still isn't ready but the power transformer has a separate winding for bias that i will bridge rectify and use as the negative supply for the mosfet. For the positive supply i'm still thinking and i'm open to suggestions

[SoulFetish]

Hello everybody,

I'm working on an homebrew design where i would like to try triode connection and class 2 but i'm having trouble in finding a datasheet that provides the curves of a triode strapped 6L6 at quite high voltages

Thats because the max plate/g2 voltage specified for a 6V6 in a triode strapped AB amplifier is 300V.

[Cannibal]

Thats because the max plate/g2 voltage specified for a 6V6 in a triode strapped AB amplifier is 300V.

I'm talkin about 6L6 (max plate/g2 in triode strapped mode = 450v, so I am right at that point).

[SoulFetish]

I'm talkin about 6L6 (max plate/g2 in triode strapped mode = 450v, so I am right at that point).

Ha! My bad.

[nickb]

[ATTACH=CONFIG]43621[/ATTACH]

Here's the load line (my photoshop skills are very basic but I think that this one could be at least readable). In red there's the max dissipation curve, in blue the class A operation and Yellow is class AB.

I'm driving it with a couple of mosfet, the design still isn't ready but the power transformer has a separate winding for bias that i will bridge rectify and use as the negative supply for the mosfet. For the positive supply i'm still thinking and i'm open to suggestions

Those plots don't seem right to me. Here's what I get for a one of the pair of 6L6's in triode mode, Vp=450V, VG=+10 to -60 and Rpp=3.6k and taking Pdiss max as 30 watts:

[Cannibal]

Those plots don't seem right to me. Here's what I get for a one of the pair of 6L6's in triode mode, Vp=450V, VG=+10 to -60 and Rpp=3.6k and taking Pdiss max as 30 watts:

The transformer has Rpp= 1.7k because it was made for a quad of 6L6's, when drawing the load line for just a pair should I double the impedance to 3,4k, right?
Sorry to bother everybody but this is my frist attempt at designing an parallel push pull output stage and I just want to be sure before doing things.

[nickb]

The transformer has Rpp= 1.7k because it was made for a quad of 6L6's, when drawing the load line for just a pair should I double the impedance to 3,4k, right?
Sorry to bother everybody but this is my frist attempt at designing an parallel push pull output stage and I just want to be sure before doing things.

Yes, that is correct.

[Chuck H]

Yes, that is correct.

Wait.?. Doesn't that only apply if the load is adjusted to 2X the secondary spec? The transformer has a fixed ratio, and so I would think a fixed reflected primary impedance when used with the specified load.

[nickb]

Wait.?. Doesn't that only apply if the load is adjusted to 2X the secondary spec? The transformer has a fixed ratio, and so I would think a fixed reflected primary impedance when used with the specified load.

No. He is using a quad. The question was what load impedance (Rpp) does each 6L6 see?

[Chuck H]

I guess I misinterpreted post #8. Cannibal did mention a quad above, but I became confused anyway. He's manipulating the load line figure for a pair to match his build with a quad. Got it.

[nickb]

It is confusing and clarification is in order. There's a lot of halving, 'n' squarin' that need to be accounted for.

The Transformer is Rpp = 1.7K so each 6L6 will see Rpp as 3.4K. Now an Rpp of 3.4k means one 6L6 will see a load of one quarter of this i.e. 0.85k (half the turns so 1/4 the impedance). Therefore when determining the slope of the load line for one 6L6, 850 ohms is the impedance to use.

So using the given we now know it's a 1.7K transformer the plot for this situation is ( biased @ 30mA):




BTW, I've heard a few folk say they don't like the sound of overdriven pp triodes much.