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Old 28th October 2004, 12:59 AM   #1
jlsem is offline jlsem  United States
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Default 6AR6/6098 ultralinear

What are good operating points for the 6AR6 in push-pull ultralinear output, staying within class A? I am looking for about 10 watts. I currently have them strapped triode at ~300V B+ and -30V bias giving a quiescent current of ~70ma.

Any general rule for UL operating points compared to triode or pentode operation? I am using LL1682 which is approximately 8K ohms into 8 ohms and 33% screen tap.

Thanks,
John
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Old 28th October 2004, 05:02 AM   #2
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What is the max current of the tranny primary?

The real trick was using the IM meter and looking at distortion.

The curves of the tube and the curves of the tranny will amtch up better throughout the operating range with certain idle currents and plate voltages.

This tube can handle 630+ on the plates. Only 315 on the screens. Then in triode mode, because the screen is tied to the plate, you can run up to the full plate voltage.

This tube is like a EL34 in that the plate can be a lot higher than the screen. This gives the tube the ability to do the large current swings for Class-AB.

Class-A is really when the screen and plate are very close. In Ultra, they are almost exact so the tube will not vary much in idle current.

I would listen to horns, drums and other signals to see if the quick bursts are clean. The problem using a unknown tube with any tranny is how the curves match up. The quick bursts of sound from symbols, piano etc. should show how well the whole output stage is matched up.

Triode mode and Ultra should be pretty close as far as idle. Is there a recomended idle current for the tranny with other tubes??
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Old 28th October 2004, 01:11 PM   #3
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Sorry for side stepping might be useful for orginal poster
Franstar
It i run the tube in SE mode triode at say 500V is it possible. Arcoding to data sheet mention it can't do that only 400V on plate when running class A and 600 at class B. Why the diferrent ratings?
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Old 29th October 2004, 12:25 AM   #4
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Hi

There is all sorts of little bits of info that you sometimes miss that you need to flesh out a paticular circuit. Data books often repeat that same data. I lost the chance to get some real old books on tubes.

They are probably talking about when this tube is used as a AM modulator. There the tube drives a transformer that is connected to the plate supply in a transmitter.

In that situation, "kick back" from the secondary could push the voltages on the plate over the limit of the tube.

The AC plate-to-plate swing will be higher than the DC idle supply voltage.

These type tubes are meant to run high plate voltages and high impedance loads.

Class-B is when the tubes are almost at cuttoff at idle. Then the dissapation would be less then Class-A as the tube goes down to almost off when it swings minus. Class-A never goes below a certain point so the power dissapation is greater for the same power out.


The 6ar8 is listed as a sheet-beam tube with only 300V max for the plates.

The 6098 is a beam power tetrode that has up to 630V + for the plates.

I was going to try some of these tubes for Audio. The curves are unknown and they have never been used to drive audio output trannys. You need to try quick bursts of sound to see how well the tube is matched to the tranny primary and speaker load.

The the best match might be at 300V or even 200V+.

I think the only way to tell is by playing the same bits of horns or piano again and again to see how smooth the sound is.

That is what I always do to really test a system anyway.


George

The Tonemaster
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Old 29th October 2004, 01:45 AM   #5
jlsem is offline jlsem  United States
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Quote:
Triode mode and Ultra should be pretty close as far as idle.
This was the answer I was looking for.

Thanks,
John
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Old 31st October 2004, 08:52 PM   #6
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I had my "Xmas Cold" this week. I had the 6aR6-8 mixed up. I am writing film scripts and film history articles on www.independentfilmsociety.org and get pooped out.

Since the tubes are running in Class-A in either mode, then idles should be the same.

You can't run a Ultralinear stage in anything other than Class-A as the screens are at the same voltage as the plates.

Glad I could help.
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Old 2nd November 2004, 09:59 AM   #7
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Quote:
Originally posted by FranStar

You can't run a Ultralinear stage in anything other than Class-A as the screens are at the same voltage as the plates.
I think you may be mistaken here...? The output stages of amplifiers, whether in triode, UL or pentode mode can be run into class AB or class B by choosing an operating point that allows one valve to run into cutoff, i.e. the idle current being less than half the peak current.

Anyway, there are some curves here where you can see the difference triode, UL and pentode mode make to the plate charactertics at Audiomatica's website: http://www.mclink.it/com/audiomatica/tubes/807.htm I have linked to the 807 page but they have curves for other beam tetrodes/pentodes like the EL34, 6L6 etc (but unfortunately not the 6AR6). As can be seen, UL operating points are indeed similar to triode operating points.
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