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Old 11th March 2013, 02:01 PM   #1
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Default 6L6 UL Power

Hi Guys,

I cannot find much for the 6L6 in UL. A few, but nothing substantial.

Assuming a B+ of ~350V in UL into a 6K A-A load, what kind if power would one expect?

I'd like to run fixed bias and hope for around 30-40W.

Thank you!

Blair
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Old 11th March 2013, 02:20 PM   #2
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Assuming 6L6GC, here is some data.....

http://www.tubebooks.org/tubedata/HB...t_2/6L6-GC.PDF
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Old 11th March 2013, 02:26 PM   #3
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Hi,

Thank you. I have the datasheets, but not much on UL operation.

Will the Pout be about the same in AB2?

Thanks!

Blair
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Old 11th March 2013, 03:02 PM   #4
JMFahey is offline JMFahey  Argentina
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Maybe, maybe not (probably not), depending on Class AB2 design parameters, specially screen resistor values.

FWIW, it's all there, in the curves.
The 6L6 (or any other tube) does know what amplifier it's in, only "sees" the instantaneous voltage applied to its electrodes (hint hint) so if you calculate what voltages it gets at any plate/screen/grid combination, you'll know what current goes through it at any moment.
Knowing instantaneous voltage and current implies a certain impedance value which matches that.

Small problem is, graphical design is becoming another extint art, same as Cathedral bell making and many others.

Probably some of the Classic books can help you .... although using the graphic method, not much simulation available way back then.
Good luck.
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Old 11th March 2013, 05:03 PM   #5
rmyauck is offline rmyauck  Canada
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Since you want 30-40W many have run 6L6 tubes in Dynaco ST-70 amps. & 6.6K would be more ideal for lower distortion so any of the circuits those or replacement boards use would work.

Heathkit W5-M amp circuit may be worth looking at also. You could convert it to fixed biias and you may get close to the power you want.

You also have choice of the Williamson circuit or the Mullard.
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Old 11th March 2013, 05:15 PM   #6
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Thanks guys,

This is more less further research for a PPP amp using 4-5 pairs into a 1.5K load. I'm looking for around 150W.

So, with 4 pairs, it should be good for 120W or so in UL.

The bigger, better question is whether getting big power from more small tubes is better than a quad of bigger tubes?

The EL34 is also an option, but I rarely see it run on ~350V on the plates in PP.

Thanks!

Blair
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Old 11th March 2013, 05:57 PM   #7
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Quote:
Originally Posted by deicide67 View Post

Assuming a B+ of ~350V in UL into a 6K A-A load, what kind if power would one expect?
I'd like to run fixed bias and hope for around 30-40W....
To get 30 - 40 W with 6L6GB, 5881 or 807 you need 450 V (with 6k6 OPT).
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Old 11th March 2013, 06:14 PM   #8
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You want big power, yet low anode voltage.
I'm confused
Is it because you have big outputs with a 1k2 primary?
In that case, you could go for 6 6550a's. Without checking the sheets, I think they should give 60-65 per pair @ 450V into 3k5 (UL)? So that translates to almost 200W into 1k2 for 3 pairs. Reduce the voltage for longer valve life.
Instead of 6550, kt88/90/100/120 will do as well.
If the outputs have 4 ohm secondaries, you could hook those up to 8 ohm speakers to give a more friendly 2k4 primary impedance. Then you can get away with only 4 KT88s, running @ 500V for (rough estimate) 150W?

Another option would be using sweep tubes.
If you don't like the topcaps: JJ produces an octal, topcap-less EL509. They should be able to produce plenty of power, just don't ask me for operating conditions. I haven't used them (yet).
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Old 11th March 2013, 06:23 PM   #9
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Quote:
Originally Posted by artosalo View Post
To get 30 - 40 W with 6L6GB, 5881 or 807 you need 450 V (with 6k6 OPT).
If you are willing to go AB2, you can get more, even in triode. I build a PP AB2 amp, with around 450 on the anodes. With 6L6GC's I get 40-45W (triode). The clipping is so soft it is hard to decide when to stop turning it up. But that is the whole idea about AB2: keep within AB1 90% of the time, with extra headroom to handle the transients.
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Old 11th March 2013, 07:03 PM   #10
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Quote:
Originally Posted by Parafeed813 View Post
You want big power, yet low anode voltage.
I'm confused
Is it because you have big outputs with a 1k2 primary?
Hi,

Not necessarily. I'm just exploring options with power iron I currently have. If all else fails, I'm willing to buy new power transformers.

Yes, I know and have changed reflective loads by using the secondaries into different loads.

The EL34 and 6L6 are just much more cost effective than 6550 or KT tubes.
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