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Old 7th January 2015, 06:30 PM   #1
hooman is offline hooman  Iran
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Default simple tube amp for music

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a friend has asked me to make simple and low- cost tube amp for music .so first step was Choosing the Right Circuit .
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Old 7th January 2015, 07:27 PM   #2
hooman is offline hooman  Iran
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push pull circuits need more tubes and heavy iron so se always seems better
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Old 7th January 2015, 07:47 PM   #3
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You can find in the forum threads about SE ECL 82, PLC 82, or 6F3P, or ECL86, PLC86.
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Old 7th January 2015, 07:58 PM   #4
hooman is offline hooman  Iran
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Originally Posted by azazello View Post
You can find in the forum threads about SE ECL 82, PLC 82, or 6F3P, or ECL86, PLC86.
thanks ...but tiny tubes like pcl82 can deliver 8 or 10 watts to speaker in se?
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Old 8th January 2015, 02:14 AM   #5
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No, about 3-4 Wt per channel. If you need 10 Wt, you can use the sames tubes in PP.
What's the sensitivity of speakers ? If more 92 Db, SE is enough.
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Old 8th January 2015, 10:11 AM   #6
DF96 is offline DF96  England
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Quote:
Originally Posted by hooman
push pull circuits need more tubes and heavy iron so se always seems better
For a given power output and distortion level, PP will need fewer (or smaller) valves and lighter iron than SE, so PP always seems better.

SE can be simple and low-cost, which is why old wireless sets used SE. However, SE can't be low cost and good for music.
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Old 8th January 2015, 04:54 PM   #7
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by DF96 View Post
SE can't be low cost and good for music.
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Old 8th January 2015, 08:49 PM   #8
hooman is offline hooman  Iran
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Quote:
Originally Posted by DF96 View Post
However, SE can't be low cost and good for music.
6b4g se can be low cost se amp and nice sound.
about 600$ .. expensive ?
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Old 9th January 2015, 12:03 AM   #9
GoatGuy is online now GoatGuy  United States
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Actually, I agree with DF₉₆. This is not unusual.

Since I'm device-agnostic, I see decided advantages with working on designs that use optimal components and design objectives from both the vacuum and sand-based world. And, since I've determined unambiguously that one of the more "affective" sound-shaping components is the output transformer (quite paradoxically) and its inherent energy storage, I basically reserve the output stage as a tube stage.

But one need not be so "pure" when implementing the input, to limit yourself to what can be rather expensive tubes compared to the modest-cost components that are alternatives in the sand-world.

For instance, JFETs are just the Bee's Knees for bringing along the "triode response curve" to the first (not preamp) stage. They're great, and if you desire, will show smooth, break less, knee-less 2nd order harmonic enhancing amplification curves. Just like competently designed but "simple" triode tube work. Cost a fraction, last forever, take up next-to-no space, and won't get all jiggly 'cuz of stray heater A/C.

But they're really only good for about 10 gain. From input levels up to 2 volts, peak-to-peak (which for audiophile components is pretty normal on the high side). There are plenty of good 35V to 45V JFETS that do the job musically well. They do, however, require a 30 to 40 volt supply. This isn't usually much of a challenge, if you're designing from the ground-up anyway.

The "middle stage(s)", whether they're additional voltage amplification, current amplification or "combo" … or whether they're a bit of that, AND push-pull complimentary signal inversion, aren't great for JFETS - when they're supposed to drive output tubes. Real vacuum tubes tend to be the best choice, although a pretty good argument can be made for MOSFETS, as they do a darn fine job emulating pentodes, with substantial current sourcing capability. Or, although I might get howled out of here: even NPN transistors. The higher voltage ones make darn fine complimentary signal inverters.

But then "on the diagram" we head to the right, where the whole almost mystical (but clearly audible) "amplification in the vacuum" happens. I tend to prefer designing with over-spec'd transformers, as they seem to be such underwhelming components if slightly short-of-the-mark. And I also tend to use tubes that have a LOT of latitude, and not too high of plate voltage requirements. Why? Because the power supplies get ever more dangerous, ever more costly, ever more likely to deconstruct themselves catastrophically if corona shorts or other problems develop. Or, as my dear Uncle used to say, "Kid, 400 volts is enough for anybody!"

Oh, sure … there are hundreds (if not thousands) of threads here about the magnificent triodes in their Big Glass Bottles, with their anode caps and their 1200 volt supplies. There are endless hints that MOSFETS might actually substitute or … (horrors) augment … more commonplace output tubes, without ruining their fundamental characteristics.

Maybe. But I don't agree. I think the output tube section's design is crucial for how the amplifier is going to "sound" with a set of relatively unknown (but let's say "competent") speakers. Big iron, lots of henries, a good match of speaker-to-plate impedance. Who could ask for more?

KT–66, 88, 120 … all good. Parallel 6L6 or cheaper 12L6 or with care, 50L6's, are fine. But remember - a good output transformer is really important. It is what separates "sound" from "music", if everything else in a system were the same.

Thank you for tolerating this unsolicited soliloquy …

GoatGuy
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Last edited by GoatGuy; 9th January 2015 at 12:06 AM. Reason: typos typos typos
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Old 9th January 2015, 12:06 AM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by hooman View Post
thanks ...but tiny tubes like pcl82 can deliver 8 or 10 watts to speaker in se?
Hi,

Get realistic, the PCL82 can max out at about 2W in a really
good SE design, and quite a lot lower in a simple SE design.

Two PCL82's in pushpull can do 8W max, typically lower.

rgds, sreten.

Maximum power is inversely related to expected tube life.

FWIW the iron required for the above two cases is the same
moreorless, as a simple approximation. Output windings of
course must differ, and the SE core needs an air gap.
Mains transformer is very similar for both, except
for the heater windings needing twice the juice.
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Last edited by sreten; 9th January 2015 at 12:22 AM.
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