One (1!!) transistor clapping...

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#141
fdegrove said:
Where's the logic gone to now?
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Hasn't gone anywhere.

A power MOSFET isn't just a single really beefy MOSFET device. It's made up of gobs of individual MOSFETs built on the same substrate and all wired in parallel. That's how power MOSFETs are able to handle that kind of power. It's like taking a whole bunch of small signal bipolar transisotrs and wiring them up in parallel in order to allow for higher power capability. Only with the power MOSFET, they're all built on the same substrate.

So technically, a power MOSFET is not truly a single active device but a composite active device made up of gobs of smaller individual active devices.

Now, if you define that as a single active device, then a Darlington transistor, which is made up of two transistors built on a single substrate, would also be a single active device. In which case a Darlington transistor would meet the original challenge of a single active device per channel.

And using a Darlington transistor, the transformer scheme would work just fine.

So, we need to decide whether or not to consider a power MOSFET (and similarly a Darlington transistor) as a single active device.

Uh? Sorry, you lost me on the logic here too...Say what????
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I'm simply saying that a single bipolar transistor (as opposed to a Darlington pair) or a single tube triode wouldn't work very well. Well, the single bipolar transistor anyway.

Actually I seem to recall that Gordin Rankin's got a little amp that uses a step-up transformer driving a single triode tube. So apparently the transformer would work with a single trode tube after all.

se
 
#142
Hi,

And using a Darlington transistor, the transformer scheme would work just fine.
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Ah, I see...same, same but different...🙂

I'm afraid you're comparing apples to oranges, though.

Which is why I said you were looking for escape routes; a darlington would work, as would a triode or a penthode.

A Fet too, but not as easily. As you probably realised???

So technically, a power MOSFET is not truly a single active device but a composite active device made up of gobs of smaller individual active devices.
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At least 70% of the active semis are composed devices, so where does one draw the line?

So apparently the transformer would work with a single trode tube after all.
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Sure would. Just don't expect much power out of it.
No need for the input xformer either as it's better to put it in the preamp but it will work, technically speaking.

Cheers and chill, 😉
 
#143
Steve Eddy said:
Actually I seem to recall that Gordin Rankin's got a little amp that uses a step-up transformer driving a single triode tube. So apparently the transformer would work with a single trode tube after all.
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My single pentode amp doesn't have input iron (it does have output iron -- but not much), and puts out a whopping 1.4 W.
🙂

5-buck amp

dave

An externally hosted image should be here but it was not working when we last tested it.
 
#148
fdegrove said:
Ah, I see...same, same but different...🙂
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Same in that you've got separate elements built on a single substrate, different in that they're not wired in parallel. And of course different device types.

I'm afraid you're comparing apples to oranges, though.
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How so?

Which is why I said you were looking for escape routes; a darlington would work, as would a triode or a penthode.
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Yes, but they all wouldn't truly be a single active device. A Darlington is effectively two devices, a triode is a single device. A pentode's arguably a single device though the multiple grids make it a bit iffy.

A Fet too, but not as easily. As you probably realised???
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A JFET would be quite easy. Just that they don't make JFETs capable of handling the current that'd be required here to get the 5-6 watts of output power.

At least 70% of the active semis are composed devices, so where does one draw the line?
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Again, you draw the line at a truly single device. A triode for example is a truly single active device. One cathode, one grid, one plate. Not multiple cathodes, multiple grids and multiple plates all wired in parallel.

Sure would. Just don't expect much power out of it.
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Apparently.

No need for the input xformer either as it's better to put it in the preamp but it will work, technically speaking.
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Well again, Fuling originally specified an amplifier, not a buffer. And even if I were going for a buffer, I'd still use a transformer if not for voltage gain then for the electrical isolation and noise rejection.

se
 
#152
Hi,

Tom,

The Sowter 3575 on the same page could be used as well.

It's easier to drive with a tube preamp but it doesn't step up.

IMHO a stup up isn't needed but that'll depend on how you configure the output stage.

Cheers,😉
 
#153
The Sowter 3575 on the same page could be used as well.
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Hi Frank,

But with the 3575 the amp would have no gain, or are you suggesting to configure it as a common source stage? I am using somthing like that at the moment (See the schematic I postedon page one of this thread). What worries me a bit whit the common source configuration is that the gain is load dependent and a speaker is a frequency dependent load.

I am interested in trying out something like the schematic Steve posted where you have a follower output stage and some voltage gain is provide by the step up transformer.

Tom
 
#154
Hi,

I am interested in trying out something like the schematic Steve posted where you have a follower output stage and some voltage gain is provide by the step up transformer.
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Sure, in that case the 8540 would be fine.
I assume your source drives a 600R load without problems...

Cheers,😉
 
#156
Im here!!!

Watching, waiting...

I´m impressed by the response I´ve gotten from all you people!
Thanks everyone!!

Tube spud? Yes please!
Still waiting for those 6C45´s to arrive, but that´s another story.

What I had in mind when I started this thread was some kind of inductor loaded Zen-lookalike. No problems so far, as long as I can dig up a linestage that can drive the whole thing and a stabilized PSU so I don´t have to worry about bias drift.

The problem is that I want to feed my amps directly from the CDP through a 50k passive autenator and feed them with good old CLC filtered PSU´s. Maybe I´m asking too much from a single Mosfet, but I believe it was worth a try.
 
#157
Hi,

Ah...there you are...😉


Still waiting for those 6C45´s to arrive, but that´s another story.
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Considering to build the "El Spuddo" ?

The problem is that I want to feed my amps directly from the CDP through a 50k passive autenator and feed them with good old CLC filtered PSU´s.
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Add a buffer to the passive attenuator and you're done...can be OPA or TUBA...:clown:

Maybe I´m asking too much from a single Mosfet, but I believe it was worth a try.
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Can be done IMHO.
Choke loading it would turn it into an emitter follower so a dedicated SE OPT comes to mind.

Cheers,😉 😉
 
#159
Hi,

A buffer? Wouldn´t that be one transistor and one IC clapping?
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Errr...yes.

I was thinking of keeping the 50K attenuator and the buffer in a separate chassis as a preamp, you see.

The net combined result would probably go clop, clap, clop, clap...😱

Maybe if you have a MOSFET with high enough input impedance it could work...

Cheers,😉
 
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