EL84 as both driver and output stage. - Page 3

Bas Horneman · 15th June 2007, 05:34 PM

Just keep the 10k for the moment and see what it sounds like.

Ps...did you try to post another picture? I don't see the rp in green...

pwan · 15th June 2007, 08:13 PM

Quote:

Originally posted by Bas Horneman
Just keep the 10k for the moment and see what it sounds like.

Ps...did you try to post another picture? I don't see the rp in green...

Yes, here it is.

Bas Horneman · 15th June 2007, 08:33 PM

I'm not sure if there is a standard notation. But the plate resistor I think should be called Ra (Resistance Anode)

The Rp is the internal resistance of the tube? (Someone please correct me if I'm wrong)

Anyway keep the Ra 10k for the time being.

And yes, if you can add additional filtering in the form of an RC network for the driver stage and feed that with a higher B+

Dave Cigna · 15th June 2007, 09:09 PM

Generally speaking, fixed values (like load resistors) are represented by upper case letters while dynamic values (like plate resistance) use lower case.

For the subscript, both 'a' (anode) and 'p' (plate) are used, though it seems that 'p' is used mostly by people in the US. Worldwide, 'a' is more common.

So a load resistor can be either Ra or Rp. The plate (err... I mean anode) resistance of a tube can be either ra or rp.

If you're an old codger that still programs in FORTRAN then everything is upper case.

-- Dave

Bas Horneman · 15th June 2007, 09:13 PM

Quote:

So a load resistor can be either Ra or Rp.

Thanks for the explanation.

pwan · 16th June 2007, 03:34 AM

Quote:

Originally posted by Dave Cigna
....If you're an old codger that still programs in FORTRAN then everything is upper case.
[/B]

No I programme COBOL

Thanks for your advice. However, I quickly looks on a local electronic book here and a few paragraph mention that the ratio of Rp(or Ra) of the first stage and the Rg of the 2nd stage should be around 3-5 for Cap interstage coupling. Have you ever heard that golden rule?

And go thru my schematic collection (~ 14 ones) and all of them comply with that guide line. In the circuit I just posted, the ratio 150K/10K = 15 which is much higher. Will it be any problem esp. on stabability & sonic degrade?

Yvesm · 16th June 2007, 05:38 AM

Larger is better

Yves.

pwan · 16th June 2007, 10:16 AM

Quote:

Originally posted by Yvesm
A quick check with Tube CAD.
.....

Is the Tube CAD a computerized aid design software? Is it a freeware/shareware? Any hint where I can get it (at least for trial)? Thanks.

SY · 16th June 2007, 11:20 AM

It's not freeware, but it's pretty cheap. You can get it through www.tubecad.com or www.tubesandmore.com .

The "free" way to do this is by the use of load-lines and graphical construction.

Quote:

the ratio of Rp(or Ra) of the first stage and the Rg of the 2nd stage should be around 3-5 for Cap interstage coupling.

Think of that as an absolute minimum. Tubes generally show the least distortion with the highest possible loads.

vizion · 8th April 2008, 09:12 PM

how many EL84s would it take to get 4.5 watts @ 5 ohms in an OTL configuration ? 30 ?

15th June 2007, 05:34 PM	#21
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	Just keep the 10k for the moment and see what it sounds like. Ps...did you try to post another picture? I don't see the rp in green... __________________ Boatanchor amps forum My "adventures" in audio

15th June 2007, 08:33 PM	#23
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	I'm not sure if there is a standard notation. But the plate resistor I think should be called Ra (Resistance Anode) The Rp is the internal resistance of the tube? (Someone please correct me if I'm wrong) Anyway keep the Ra 10k for the time being. And yes, if you can add additional filtering in the form of an RC network for the driver stage and feed that with a higher B+ __________________ Boatanchor amps forum My "adventures" in audio

15th June 2007, 09:09 PM	#24
Dave Cigna diyAudio Member Join Date: Oct 2003 Location: Finger Lakes, NY	Generally speaking, fixed values (like load resistors) are represented by upper case letters while dynamic values (like plate resistance) use lower case. For the subscript, both 'a' (anode) and 'p' (plate) are used, though it seems that 'p' is used mostly by people in the US. Worldwide, 'a' is more common. So a load resistor can be either Ra or Rp. The plate (err... I mean anode) resistance of a tube can be either ra or rp. If you're an old codger that still programs in FORTRAN then everything is upper case. -- Dave __________________ January 20, 2009: Bush's last day

8th April 2008, 09:12 PM	#30
vizion diyAudio Member Join Date: Apr 2007	EL84 OTL how many EL84s would it take to get 4.5 watts @ 5 ohms in an OTL configuration ? 30 ?

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16th June 2007, 05:38 AM	#27
Yvesm diyAudio Member Join Date: Jul 2004 Location: Ardeche	Larger is better Yves.

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