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Old 3rd Jan 2007, 10:14 am   #1
oldeurope
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Thumbs up making an audio output triode...

Hi,
Searching for a power triode, I found a way to multiply the current of a small signal triode (ECC82) by a transistor (BU4525AXPH selected B=10).
Generally the output side of a transistor is similar to a pentode, but connected in the way shown in the pictures it is exactly like a triode. In this application modern bipolar transistors are making an output current B- times higher than the base current independent of the Collector – Emitter voltage. Bipolar power NPN transistors with a B from 5 to 50 and up to 1500V peak C-E Voltage are available. So you can make your dream audio output triode with the perfect characteristic of a small signal triode multiplied by current gain factor B. The transistor is a kind of triodemultiepler. For the test arrangement Rk = 270 Ohms Ua = 300VDC (Ug = -16V, Ia = 60mA) Ra = 2K5 Ohms gives something about 3 Watts audio output.
Happy experimentig,
Darius
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Old 3rd Jan 2007, 10:23 am   #2
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Default Re: making an audio output triode...

Hi
A circuit diagram would be welcome.
Cheers
Peter.
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Old 3rd Jan 2007, 10:29 am   #3
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Default Re: making an audio output triode...

The circuit is sketched on the graph.

It looks like a darlington pair with the first transistor replaced by a valve.

The audiophools will never buy it becuase it's got unmentionable silicon fuses in it
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Old 3rd Jan 2007, 11:43 am   #4
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Default Re: making an audio output triode...

Quote:
Originally Posted by ppppenguin View Post
The circuit is sketched on the graph.

It looks like a darlington pair with the first transistor replaced by a valve.

The audiophools will never buy it becuase it's got unmentionable silicon fuses in it
Yes, but I think there are a lot of more technical audioenthusiasts who want to build and test ist. It is so easy and the result is perfect. I tried to find something similar at google but I didn't. Often you find something infront of a transistor amp to get triode sound. This is definately not the same!

Darius
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Old 3rd Jan 2007, 12:24 pm   #5
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Smile Re: making an audio output triode...

typical application circuit attached:
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Old 3rd Jan 2007, 2:35 pm   #6
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Talking Re: making an audio output triode...

@Jeffrey, what do you think about the following names:
triodemultipler, valvelington, tubelington, triodelington?
Other suggestions are welcome, hi hi.


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Old 3rd Jan 2007, 3:07 pm   #7
mickjjo
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Default Re: making an audio output triode...

The Transiodarius .

Regards, Mick.
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Old 4th Jan 2007, 1:15 am   #8
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Default Re: making an audio output triode...

Hmm....i like this.

So, techically, a small triode and a massive transistor can be used to give lots of power.

Nice idea!!!
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Old 4th Jan 2007, 7:51 am   #9
oldeurope
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Default Re: making an audio output triode...

I will use both systems of the ECC82 in parallel. Than the circuit is equal to eleven (!) ECC82 in parallel. Each triode system of the ECC82 has about 5mA at 250- 300V so long live is guaranteed. This will give 5W or a bit more. Enough for a triode amp. The power dissipation will be about 25W. Next week I'll make some nice output transformers for this triode multipler arrangement.
Hi adibrook, only 20% from the dissipated power comes to the speaker. So a triode is not an economic way to get a lot of power.

Darius
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Old 4th Jan 2007, 8:26 am   #10
Mike Phelan
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Default Re: making an audio output triode...

Almost like some of the old car radios that had E??83 12 volt HT valves and an OC16 for output! Except they were not direct coupled.
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Old 4th Jan 2007, 9:43 am   #11
oldeurope
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Unhappy Re: making an audio output triode...

Quote:
Originally Posted by Mike Phelan View Post
Almost like some of the old car radios that had E??83 12 volt HT valves and an OC16 for output! Except they were not direct coupled.

Oh dear, sorry, there is a misunderstanding.Driving a transistor with a valve (triode) DC coubled or not doesn‘t create a triode output in general!
It is the special arrangement I showed above that makes the triode output.

Kind regards,
Darius
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Old 4th Jan 2007, 9:58 am   #12
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Default Re: making an audio output triode...

Wow I really like this idea! I suppose it'd work with a small signal pentode too right? If you set the screen up right.

What kind of transistor is that anyway? How would you go about choosing an equivalent if you couldn't get your hands on that one?
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Old 4th Jan 2007, 10:13 am   #13
oldeurope
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Default Re: making an audio output triode...

Quote:
Originally Posted by Merlin View Post
Wow I really like this idea! I suppose it'd work with a small signal pentode too right? If you set the screen up right.

What kind of transistor is that anyway? How would you go about choosing an equivalent if you couldn't get your hands on that one?
You mean screen and anode parallel = triode?

Darius
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Old 4th Jan 2007, 11:01 am   #14
Merlin
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Default Re: making an audio output triode...

Quote:
Originally Posted by oldeurope View Post
You mean screen and anode parallel = triode?
Um, well for normal triode operation you'd connect the screen directly to the anode. I was thinking of running the screen separately as in normal pentode operation. The transistor would then amplify its characteristics and you'd have a power pentode? I may of course has misunderstood this whole idea!
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Old 4th Jan 2007, 11:25 am   #15
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Default Re: making an audio output triode...

Quote:
Originally Posted by Merlin View Post
Um, well for normal triode operation you'd connect the screen directly to the anode. I was thinking of running the screen separately as in normal pentode operation. The transistor would then amplify its characteristics and you'd have a power pentode? I may of course has misunderstood this whole idea!
Hi Merlin,
a transistor and a pentode do have the same output characteristics.
And there are a lot of nice pentodes available, so this makes no sense to me.
If you connect the plate of the driving triode to a fixt positive voltage the arrangement has the same characteristics at input and output like a pentode.
I want to have a (power) triode.

Darius
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Old 5th Jan 2007, 9:48 am   #16
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Default Re: making an audio output triode...

Well I was thinking you'd be able to get the characteristics of the small pentode (which sounds nicer than a transistor), but be able to use it as a power pentode. So it'd sound like a pentode and not like a transistor...

Incidentally, hot were you thinking of setting this up as an output stage? With an output transformer between HT and the anode/collector as usual?

Here are some more names too, "valvistor", "triistor" (or tri-istor), "tristor"!
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Old 5th Jan 2007, 2:29 pm   #17
oldeurope
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Default Re: making an audio output triode...

Quote:
Originally Posted by Merlin View Post
...
Incidentally, hot were you thinking of setting this up as an output stage? With an output transformer between HT and the anode/collector as usual?
...
Yes, as usual.
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Old 8th Jan 2007, 9:41 am   #18
Merlin
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Default Re: making an audio output triode...

I've only just noticed you posted a typical circuit above. What is the zener diode for? Surely the ECC82 doesn't need protection from overvoltage?
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Old 8th Jan 2007, 2:19 pm   #19
oldeurope
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Default Re: making an audio output triode...

Quote:
Originally Posted by Merlin View Post
I've only just noticed you posted a typical circuit above. What is the zener diode for? Surely the ECC82 doesn't need protection from overvoltage?
It is to make sure that there isn't more than 1000V at the plate/collector.
Darius
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Old 8th Jan 2007, 7:01 pm   #20
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Default Re: making an audio output triode...

Great work, Darius.
Have you carried out any distortion analysis? Power Triodes produce mainly
2H ofcourse.
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