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Question: Class AB Hybrid with small signal triode and Power Mosfet output?

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Question: Class AB Hybrid with small signal triode and Power Fet (or BJT) output?

I'm curious if a couple of favorite things would combine decently?
Small signal Russian triodes run on regulated/capmulti power + Power Fet (inexpensive latfet) or BJT output devices, Class AB, (without output transformers). Well, that should be remarkably efficient and cost effective for a tube hybrid.

Will these things go together as nicely as peanut butter on chocolate, or as poorly as peanut butter on hot dogs?
 
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This certainly works but the choice of the front end tube is not at all trivial. Ig you want consistent performance of the output stage throughout the audio band, there has to be realtively a lot of current available from the tube stage - relatively to usual tube currents. Or, you need an intermediate driver/follower.
The MOSFET stage will present a rather high and, worse, nonlinear, capacitive load for the tube front end (on the order of hundreds of pF even for a single pair of lateral FETs). That being said, even a simplistic design, say ECC88 (and family) in SRPP driving a single pair of laterals can produce more than just usable results if set-up properly, but there are also better ways to do this.
BTW a single pair of lateral MOS even at hihg standing current (and 100-150mA is the usual value) has a rather high output impedance and damping factor. Unless you want to go through a mix-and-match procedure to find the best suited speakers, expect to need some NFB to sort this out, but then the choice of input tube becomes even more non-trivial, as it also has to provide excess gain for the NFB to work with.
 
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Attached is one possible powerfet output device.
It does need added global negative feedback.
I don't know if this device is suitable.
 

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Sorry, I should have known better. Any mention of that chip would usually come with the comment "needs work" except for tone amp, tv amp, and guitar amp. Please disregard the chip posting. :)

Next, I go to search for dmos/powerfet/latfet at Mouser. Wow. Epic challenge. They've got some, but they're tossed right in with about 3000 "ordinary" mosfets. AudioWind and ElectronicsSalon do list some (authentic) lateral and power mosfets, probably for audio use, but they are just a bit expensive.

I'm actually after a beginner's doable, low cost, high resolution tube hybrid amplifier, and if laterals are a bit difficult, then BJT would be okay.

On hand "sand"
I do have KSA1220A, 2SC5171 and MJL0302 and their compliments in addition to BC556B, BC327-25,40 their compliments and their higher voltage counterparts. So, perhaps small signal triode + low noise/high linearity BJT would be more doable?

Tubes
On-hand tubes include 6N3P-E, 6N1P-E.

Power
I've intended to use an SMPS plug pack with plenty of knots in the cord for heater supply, LM317, LM337 for front end regulators, Fairchild Stealth bridge rectifier and unreg power with transformer specs TBD but I'd like to use affordable 63v caps in split rail power.
 
Its such a shame that this sort of thing can't be used for low cost, good performing beginner's projects.

So, I take it that a minor problem with a tube hybrid is getting enough open loop gain so there's enough margin to make negative feedback work?

And a major problem is possibly that all the tube hybrids are either well kept secrets or somebody's intellectual property because, of course, tube hybrid (small signal tubes + solid state outputs) is both low cost and extremely profitable?
 
Did you use the search function on this forum ? Take a whole day and just read some old posts, please. You will be suprised how much information there is which you need.

Next, I go to search for dmos/powerfet/latfet at Mouser. Wow. Epic challenge. They've got some, but they're tossed right in with about 3000 "ordinary" mosfets. AudioWind and ElectronicsSalon do list some (authentic) lateral and power mosfets, probably for audio use, but they are just a bit expensive.

-> Search function. Key words: profusionplc, Exicon, Semlab

Power
I've intended to use an SMPS plug pack with plenty of knots in the cord for heater supply, LM317, LM337 for front end regulators, Fairchild Stealth bridge rectifier and unreg power with transformer specs TBD but I'd like to use affordable 63v caps in split rail power.

If done properly, tubes need a high voltage supply. If you buy a nice "classic" transformer or use something like this is up to you.

Its such a shame that this sort of thing can't be used for low cost, good performing beginner's projects.
The question is what one defines as beginner project. Tubes are pretty easy to get by with. Much easier than discrete solid state parts. We're facing a different problem today. Many people think, that a chip amp is already complex enough.

So, I take it that a minor problem with a tube hybrid is getting enough open loop gain so there's enough margin to make negative feedback work?

Erm..well..no..why ? It is up to you. With a simple source/emitterfollower you don't need any feedback at all. The schematic which Ketje posted is the opposite, a drainfollower with hexfets. Can be frustrating to keep such topologies from oscillating. Don't build that....

And a major problem is possibly that all the tube hybrids are either well kept secrets or somebody's intellectual property because, of course, tube hybrid (small signal tubes + solid state outputs) is both low cost and extremely profitable?
Oh boy :rolleyes:
That is the wrong way to think about this hobby. This almost sounds like resignation. Why do you care about "well kept secrets" etc. ? Don't make a mistake and believe you hit a gold adder because you found out about hybrids. There is no damn secret. How many bad hybrid amps may be out there ? How many better LM3886 amps may be out there ? Don't try to look for the holy grail - there is none. There are so many books out there and even a free simulating tool called LTSpice. You a free to design everything you want. And that is what this is all about.

But of course, I will try to help and support you :)

Here a few links to some Hybrids:

Moskido from John Broskie:
Moskido & Audio Note's Feedforward Shunt Regulators
DIYAudio Thread: http://www.diyaudio.com/forums/tubes-valves/102613-moskido-hybrid-aikido-mosfet-amplifier.html

Hybrid from AudioXpress:
http://www.stephenwmoore.com/SMOORE Hybrid Amp Part 1.pdf
http://www.stephenwmoore.com/SMOORE Hybrid Amp Part 2.pdf

6Н3П-Hybrid (written in lovely german ;)):
Hybridverstärker mit der russischen Röhre 6N3P

Andrea Ciuffoli-Hybrid:
Hybrid Amplifier by Andrea Ciuffoli
 
Yes, something quite like that, no output transformer, and not expensive. However, I would like Class AB output.

The Aikido documentation is pretty good reading and has:
complete_transistor_output.png

Yes, the transistors are interesting. Can the types be upgraded and the circuit be changed to class AB?
From here: Aikido PCBs and Aikido hybrid power amplifiers

P.S.
This soft clippy is mildly interesting:
Hybrid amplifiers and soft-clipping circuit
 
How many better LM3886 amps may be out there?
It is quite wonderful as a subwoofer/bass amplifier. I've tried 6n3p buffer, Parallel LM3886 amp, high capacitance output caps (cheap protection + big bass tuning fun), driving a sturdy 4 ohm woofer, resulting in 90 watts of very high quality bass. It was also useful to have a passive 2nd order parallel crossover on that woofer so that the spike system hard clipper harmonic distortion was effectively blocked. The overture chips are also good as bass amp portion of a high fidelity bi-amp system, because the bass through bari range is beautiful indeed.
And, the Overture chips are capable of rendering the midrange and treble in a standout piercing clarity; However, I would rather have something more palatable for loud replay fun and therefore won't be using an LM3886.
Thank you! I'll be doing a lot more reading.
 
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