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Old 4th December 2004, 12:13 AM   #1
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Default EL84 SE design recommendations?

Anyone know of a proven designs using the EL84s either in pentode or triode mode? There are too many designs out there and I wanted to find a few designs that have been built and heard.

Also, is there a particular driver tube that sound good with the EL84?

Few examples I found:
http://www.bonavolta.ch/hobby/en/audio/el84.htm
http://www.tubeaudio.8m.com/RH84/rh84.html
http://www.angela.com/catalog/how-to/SE.EL34.html


TIA...
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Old 4th December 2004, 05:28 AM   #2
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Default Re: EL84 SE design recommendations?

Quote:
Originally posted by RockysDad
Anyone know of a proven designs using the EL84s either in pentode or triode mode? There are too many designs out there and I wanted to find a few designs that have been built and heard.

Also, is there a particular driver tube that sound good with the EL84?
Build a circuit design with the '84 in triode or pentode at 250V B+, and play with a variety of different driver tubes. Pull the op points off the Mullard datasheet. This is the easiest power tube to drive well. Almost anything except a 12AX7 will do, just because they stink so bad. try 12AU7, 6SN7, ECC99, 6FQ7 etc and find the flavour you like best.
It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design. The Grounded Cathode Tube article on Tubecad explains how to do it (for the driver and the Mullard sheet tells the '84 pent and tri op points.

Unless you use NFB, a pentode will have a very high output Z, which might not ba a problem if you use a low Q driver like a Fostex.

Blech. The EL34 is a different animal.
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Old 4th December 2004, 05:53 AM   #3
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Quote:
Blech. The EL34 is a different animal.
Oh, wow.. Brain freeze...

Quote:
It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design. The Grounded Cathode Tube article on Tubecad explains how to do it (for the driver and the Mullard sheet tells the '84 pent and tri op points.
Is it? I read that article some time ago but never fully understood whats going on. Also, I never figure out how the driver and power sections work together. That where I sort of left off but maybe I'll try and reading it again. Maybe this time I will understand it better since Il have a project in mind when I read it. Wish me luck. I know I will have questions though...

Thanks...
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Old 4th December 2004, 05:53 AM   #4
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Default Re: Re: EL84 SE design recommendations?

Quote:
Originally posted by Brett
Blech. The EL34 is a different animal.
Exactly. The things which the EL34 shares with the EL84 are:
- 6.3V heater (E)
- Output beam tetrode/pentode (L)

Quote:
Originally posted by Brett
It's really easy, and if you do it from scratch you'll learn a LOT more than simply building another person's design.
Agreed as well. And it's much more satisfying!
Some other links for basics:
Diyparadise
Steve Bench (go to the "Of Loadlines Power Output and Distortion" series.

If you need help, ask!

Sorry, that was a bit of a me-too post...

EDIT: Oh, I see you posted while I was typing...
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Old 4th December 2004, 06:29 AM   #5
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Default Re: Re: Re: EL84 SE design recommendations?

Quote:
Originally posted by RockysDad
Is it?
Yes.
Quote:
I read that article some time ago but never fully understood whats going on. Also, I never figure out how the driver and power sections work together. That where I sort of left off but maybe I'll try and reading it again. Maybe this time I will understand it better since Il have a project in mind when I read it. Wish me luck. I know I will have questions though...
It's best to learn with a specific application in mind.
I had a guy recently ask me about tubes and wanted to learn, so we set the specs for a project (guitar amp) and it's progressing from there as he can see the direct relationships between the theory and practice as me just explaining the dry theory wasn't getting anywhere.

Quote:
Originally posted by audiousername
If you need help, ask!
Yep.

Re-read the tubecad article, pick a driver from the list I gave above, try some values for anode and cathode resistors, post them and get a critique.

To simplify it, I think you should try a triode design first (o/p impedance issues), so the Mullard specs are
Vanode = 250V
Ianode = 34mA
Vgrid = -9V
Rload = 3500 ohms
Rcathode = 270 ohms
Power = 1.5W (enough?)

Assume the B+ for the driver will 250V too and work from there.

Buy cheap and/or surplus parts (and resell them to finance the next project) and use this as a learning exercise.
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Old 4th December 2004, 10:20 AM   #6
GeirW is offline GeirW  Norway
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Gday.

@RockysDad.
Regarding 84SE, i think you should look at the SE 1. & 2.
at bonavolta. The same schematics can also be seen at
http://www.tubebuilder.com/schematic2.html
where the design with EEC82 seem to be rated better.
Yesterday, i did come by another one, with ECL86
(can`t remember where)
but this one was givin 5.7W, pretty much the max. for EL84
at 250. I think that one have to much ditortion.

Haven`t a clue about the one at
http://www.tubeaudio.8m.com/RH84/rh84.html
looks interesting though.
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Old 4th December 2004, 06:39 PM   #7
GeirW is offline GeirW  Norway
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Gday.

Another one:
http://members.at.infoseek.co.jp/lagarto/el84seamp.png
Quote:
peak power are 4.5W and 5% distortion are 3.8 W.Freq response are 20Hz to 50Khz -3dB at 1W rms. very natural
sound
edit/
in above post, it is a EF86
Attached Images
File Type: gif el84 single-ended 4.gif (19.3 KB, 6448 views)
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Old 5th December 2004, 09:11 AM   #8
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The schematics GeirW referred to all have the EL84 operating in pentode mode, which (as Brett has already eluded to) may well cause output impedance issues (though the importance of this will depend on your speakers).

Since suggestions are coming... I might add the Decware Zen to the list. The schematics are there somewhere on the Decware site, and it will have lower distortion and lower output impedance than running the EL84 in pentode mode (and lower power). Oh, and of course it's a proven design. Yes, it uses the SV83 but could probably be easily modified for EL84s, or you could just buy some SV83s.

Still won't beat the satisfaction from designing AND building something yourself from scratch though...
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Old 5th December 2004, 10:25 AM   #9
GeirW is offline GeirW  Norway
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Gday.

This ZEN amp looks interesting.
Low part count, cheap tubes, simple design.
@AUN. do you know the component values,
(small pic./bad eyes.)
btw. is the psu there to.

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Old 5th December 2004, 11:28 AM   #10
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AUN? I assume that's me. Don't like the name but typed it in without thinking at sign-in... What can you do...

Save the schematic to file and zoom in with Acrobat Reader

Not sure what the OPT primary Z is. I remember reading somewhere that it is very high (like 9K8), which would be consistent with SD's claim of increasing power with lower impedance speakers.

Anything else, just ask.

BTW: Decware sells kits for the Zen with all the parts (inc the transformers, whose specs aren't listed on the schem) for US$399.

EDIT: If you want to see how hard it is to assemble, there is a detailed step-by-step instruction manual here.
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