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Old 23rd December 2012, 08:29 AM   #1
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Default Typical power for tubes

i have a fairly straightforward question for you. with a standard, nothing-fancy type of circuit, what tubes put out what power? do they all work in pairs (quads, sextuples, etc)? and also which one do you design with and why? like what should i expect from 4 6L6? is that more power than 4 6V6? what kind of power does a pair of EL84 put out? EL34? what other common power tubes are there to choose from? not building anything, but considering having something built. i just need a little more basic education about those majik glass jars.
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Old 23rd December 2012, 10:06 AM   #2
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You can get much information by studying the datasheets of the tubes under question.

In principle you get more power with higher plate voltage. Fixed bias will give higher power than cathode bias.

Let's consider EL34 as push pull and with fixed bias first:

Supply voltage ..... Pout
400 V ..... 55 W
350 V ..... 36 W
500 V ..... 70 W
800 V ..... 100 W

With cathode bias:

375 V ..... 35 W

All output tubes can be connected as quads or sextuples as well.

6L6 is essentially more powerful tube than 6V6 and the output power from 6L6 is greater as well.

For 4 x 6L6, 450 V supply voltage and UL-connection the estimated power level is some 70 W. If pentode connected, then some 80...90 W is expected.
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Old 23rd December 2012, 10:15 AM   #3
GeorgK is offline GeorgK  Austria
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Roughly speaking, in a usual Class AB configuration, a pair of 6L6 or EL34 reaches about the famous 50-60 Watts, 6V6 about 20-25 and EL84 about 15-20 Watts.
These are very rough values, it depends on how much the design stresses the tubes (by voltage, bias...). Also not applicable for cathode biased or Class A power stages, these put out less power.
For quads/sextexts just double/triple these values.
Essentially among the tubes you mentioned there are two families, one being the EL34/84 ("real" pentodes) and the other the 6L6/6V6 (beam power tetrode)types. Deciding which one to use is IMHO rather a question of philosophy and taste. The EL's are argueably the technically better types (I know some will not agree), but many (including me) prefer the "american" and by tendency smoother sound of the 6L6/6V6.

edit: sorry artosalo, you were typing faster, but I think we get to the same conclusion

Last edited by GeorgK; 23rd December 2012 at 10:18 AM.
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Old 23rd December 2012, 10:16 AM   #4
JMFahey is offline JMFahey  Argentina
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Start by googling the desired datasheets , they suggest many configurations in different power ratings.
Also google some classic tube amp schematics, see what they use.
EDIT; wow, talk about simulposting
Looks like we all just woke up.

Last edited by JMFahey; 23rd December 2012 at 10:19 AM.
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Old 23rd December 2012, 12:00 PM   #5
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I've twice used the 6CA7 version of the EL34 in my ST70 amp,. If the electrolytic cap was fairly new, the 5AR4 rectifier hot, and the B+ over 400 under load , I could get 17.5 VAC average into an 8 ohm resistor. That is about 38 watts. I bought new JJ 6CA7's in 2010 to replace the GE's that tired out in 1982. They are hitting the mark again. I had Mullard UK made tubes, probably EL34, from 1970 to 1976, they hit the 17+ volts on a Radio Shack meter. I now use a Simpson 266 VOM so these are average AC voltage readings. I've hit that peak voltage with new parts 3 times over the years, then as I use it the power gets more and more polite (no peaks). This time I used >3000 hour service life radial lead capacitors instead of the Sprague atomlytic bundle (the first replacement) or a CDE multisection can the second replacement. That was always the part that wimped out the first.
My Hammond H182 organ has 6BQ5 outputs on 8 ohm speakers. It sounded very tired when I got it, sort of like an electric kazoo, with 45 year old B+ caps. I put new 50 uf film genelec motor capacitors after the 5AR4, and a new tall can CE electrolytic cap over in the amp chassis. With 45 year old Hammond brand tubes, 420 Vdc B+, on 3 notes at a time into an 8 ohm speaker (not measured) it was getting 20 V pp on a scope. I'm a little vague whether that is 14 vac average and 24.5 watts, or 7 vac and 6.1 watts. The datasheet says these are 13 W max push pull so probably 6.1 w. Plenty of bass though, enough to rattle the window pane. The bass speaker is GE 7591's push pull, 35 v pp with the new caps behind it,
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Last edited by indianajo; 23rd December 2012 at 12:13 PM.
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Old 23rd December 2012, 12:24 PM   #6
GeorgK is offline GeorgK  Austria
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Quote:
Originally Posted by indianajo View Post
I'm a little vague whether that is 14 vac average and 24.5 watts, or 7 vac and 6.1 watts.
7 VAC is correct! 10V peak Voltage is the correct calculation base then, and for sine waves this means 10/(sqrt2)=7,09Veff.
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Old 24th December 2012, 03:18 AM   #7
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I'd love to find some EL34s that could handle 800 volts on the plates for a couple of hours.
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Old 24th December 2012, 04:36 AM   #8
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Quote:
Originally Posted by Keriwena View Post
I'd love to find some EL34s that could handle 800 volts on the plates for a couple of hours.

Don't be confused between the difference of anode voltage and anode dissipation. The maximum anode dissipation of EL34 is specified as 25 W.
When the anode voltage is 800 V, then max. anode current may then be some 31 mA.
Actually EL34 is specified to handle even 2 kV anode voltage when it is not conducting ( max. Uao = 2kV ).

At fifties Geloso built an amplifier G280A with a pair of EL34 as output tubes with 1000 V anode voltage.
G280A Amplifier Geloso SA; Milano, build 1958, 4 pictures
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Old 24th December 2012, 08:31 AM   #9
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Quote:
Originally Posted by artosalo View Post
Don't be confused between the difference of anode voltage and anode dissipation. The maximum anode dissipation of EL34 is specified as 25 W.
When the anode voltage is 800 V, then max. anode current may then be some 31 mA.
I was thinking more along the lines of raising the B+ in a guitar amp and getting about 160 mA. For a short time.


Anyway, GeorgK has the answer in his first line, though in a guitar amp I think EL84s are louder than 6V6s, at least for variations on the 18 watt Marshall theme.

Last edited by Keriwena; 24th December 2012 at 08:35 AM.
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