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Old 30th October 2007, 12:39 AM   #11
rdf is offline rdf  Canada
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Hi Audio_idiot. I've played around with triode-EL84 driving triode-EL84 SE without getting too far because of microphonics. None of the half dozen brands in-house cured it. Something to watch for.....
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Old 30th October 2007, 11:11 AM   #12
18thell is offline 18thell  United Kingdom
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Default Re: 5W EL84 drive EL84 SE

Quote:
Originally posted by Audio_idiot
Hi 18thell,

The Mullard datasheet did shows 4.5k load for pentode and 3.5k for triode. But could you kindly elaborate how the 15k grid input is determined?

Woud love to hear some comments on choke loading the plate too.
Cheers
For the music industrial equipment, they will set the output impedance to 600ohms, and the input impedance of the power amp is 15k.

Usually the input impedance of a power amp. if too high, noise is large, reverse is small, but if set the input impedance too low, it will damp down the output of the preamp. cause not enough drive voltage, cannot achieve max. output power.

For preamp, the output impedance is 600ohm, thus it can drive tenth of power amp. without low down the output voltage, because the input Z of the power amp is considerable high.

To set the input impedance is by setting the ground grid loading, one is by resistor, the other is transformer, transformer divided into AF, and RF, as U said, choke loading is a kind of method.

In AM transmitter, the AF modulation either by ! : ! transformer ratio or using choke coil. these method widely used on plate modulation.

Plate load could be anything, resistance, inductance, resonance cct.
depends on the application.
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Old 6th November 2007, 07:08 AM   #13
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Hi guys,
Was away for work, sorry for the late respond.


18thell,
Thanks for you clear explinations.


Simpleton, Shoog,
Thanks for you pointers. I really like the idea of the compact PP amp. I'd actually built 2 power amps with the same topology, an EL84 to the dot (DIYPARADISE'S CIRCUIT) and a RU32 with CCS which I fiddle around with the design. They actually sounded very much like SE.


RDF,
I was warned about the microphonics... but I was also told that EL84 can actually sing very well! that's why I was keen to have a go at it. Did you like what your hear? i.e. if we can just forgo the microphonics?


Cheers
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Old 6th November 2007, 11:44 AM   #14
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Glad to hear you like it

Now, some photos... :P
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Old 6th November 2007, 08:52 PM   #15
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Hello,

as coincidence would have it, I designed such an amp recently.
I have built several amps with an EL84 as driver, even an IT coupled LCR RIAA phono preamp.

The EL84 is a great driver tube and gives a fantastic sound.

Here is the schematic:

Click the image to open in full size.

I do not recommend ultralinear mode.

Feel free to ask any questions you might have.

Best Regards
Michael
www.tubemaster.de
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Old 6th November 2007, 09:30 PM   #16
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Did you try using the driver tube as pentode? Or am I swearing by asking such a question.
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Old 6th November 2007, 10:03 PM   #17
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Quote:
Originally posted by Bas Horneman
Did you try using the driver tube as pentode? Or am I swearing by asking such a question.

Hello Bas,

no it's not that bad I like the pentode on the output a lot but for input I prefer a triode.

The pentode/triode switch on this amp changes the sound character considerably. While triode mode is more neutral, pentode mode is more tuby, maybe even better than real.

Best regards
Michael
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Old 6th November 2007, 11:50 PM   #18
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Hi simpleton,
I built the EL84 first by following the circuit to the dot, after which I canabilised the OPT for the 832. will post some pix sine your are interested. I actually regreted this as I really prefer to listen to the Simple EL84. BUT I left it as it was because 832 has that cool look


Tubemaster,
Thanks for sharing your design.
Why not UL?
I read that pentode with small load could sound great, is this the case here?

Cheers
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Old 7th November 2007, 03:34 AM   #19
rdf is offline rdf  Canada
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Quote:
Originally posted by Audio_idiot
Did you like what your hear? i.e. if we can just forgo the microphonics?
Sorry A_I, the only thing I remember was, finding a sustain in the two second range, I went in a different direction.
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Old 7th November 2007, 05:31 AM   #20
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Just took my 832 off the shelf for this pix
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