Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on July 15, 2016, 11:54:55 am
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does anyone have a circuit for a nice sounding 40 watt power amp using only one tube? i feel like this is a more complicated question then i think...
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does anyone have a circuit for a nice sounding 40 watt power amp using only one tube?
Marshall Valvestate 8040 matches that criteria.
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Hi there !
You may want to check out this thread (http://el34world.com/Forum/index.php?topic=20353.msg214204#msg214204), it is a very interesting circuit !
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Marshall Valvestate
:l2:
I've had the pleasure of fixing a few of them!
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> 40 watt power amp using only one tube?
Sluckey's answer fits the technical specs.
You need gain. A single triode/pentode does not give enough gain to come-up from guitar level to loudspeaker level. There are triode-pentode bottles which give some power output (a few Watts) and almost enough voltage gain to be driven from guitar. There is a triode-triode-triode which would give the gain but only part-Watt output.
If you mean "one power tube" (admitting that you still need other small tubes)--- a "one tube" power stage must run class A, and therefore will not be over 50% efficient. With tubes, 40% efficient is doing good. Therefore a 40 Watt audio output amp needs a tube which will dissipate 100 Watts at idle.
Our Usual Suspects go 25-35 Watts Pdiss, to 42 and 60W for some extreme cases.
There are Transmitter tubes to 10,000 Watts and more. Generally they are very fussy about filament voltage, start-up process, overload protection. Also rare thus costly. Most want extremely high voltage and high load impedance, both awkward for audio amplifiers (they work better as radio transmitters).
HK-257 has a datasheet condition for one tube, 30 Watts audio output. This needs 1,000V supply, a 12K load winding on a core which will take 75mA without saturation. This is a VERY expensive transformer. An HK-257 plus an OT will cost much more than a couple 6L6 with standard OT, even including labor for extra socket. (IIRC the socket alone for HK257 costs more than a 6L6.)
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I don't remember how many W the amp give, but DummyLoad builded a "champ" that uses one BIG power tube (4E27)
(http://el34world.com/Forum/index.php?action=dlattach;topic=10262.0;attach=19506;image)
http://el34world.com/Forum/index.php?topic=10262.0 (http://el34world.com/Forum/index.php?topic=10262.0)
Franco
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After seeing Dummyload's big Champ I just had to check the Data sheet on that tube.
That one takes 7.5A of 5V just to light it's heater. :w2:
With 1000V on it's plate and 300V on it's screen the specs say 34W output.
Have you run across some free transmitter type tube gear?
The PT and OT required for that type of amp would be very HEAVY and very expensive.
It's much easier, cheaper, and lighter to get 40W from a pair of 6L6s, IMHO. :dontknow:
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I think this was more of a drive by brain teaser, actually.
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And that's why my valvestate answer was appropriate. :icon_biggrin:
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I did have quite the chuckle when I looked up that schematic!
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The audiophile guys can provide tubes that meet your spec, and they are using triodes. Expect to pay new amplifier costs for a single tube.
KR Audio makes or sells the tubes.
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I think this was more of a drive by brain teaser, actually.
Considering its 5 days later and the OP hasn't responded to questions, I'd say so :)
~Phil