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Old 28th August 2002, 05:18 AM   #1
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Default EL84 and EL34 sound

Has anyone used the EL84 or the EL34 in triode mode in any stage other than a tube output stage ? If so what do you think of its sound quality. I read somewhere that the EL 84 was very well regarded - is this true?
I want to use it as a driver in a hybrid amplifier and am not sure which tube is better. I think the EL34 is used by someone in this kind of application.
I find lots of problems with interstage RC coupled hybrid amplifiers which have overall feedback. They tend to oscillate at very low frequencies on overload. Though it is a highly damped oscillation it can cause lots of problems.

Thanks.
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Old 28th August 2002, 08:19 AM   #2
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I built an EL34 amp years ago, which I still listen to from time to time. It's a typical Mullard P-P configuration with 12AT7 front end and 12AU7 phase splitter. I set it up with switchable output configuration - either "triode" mode or ultralinear. In general, I prefer the ultralinear mode. I'd definitely like to try it up in pentode mode too, but the amp is not really suited for modification... one of my first P2P wired projects (yes, most of my early projects actually used hand made PCBs!) it is really awkward to work on, and crammed into it's case on a double-sided punchboard suspended below the lid of the chassis. Good thing I've figured out some better construction methods...

Anyway, I find the triode mode is a little too soft, and fine detail becomes obscured. Perhaps at different bias levels it would sound different, but the distortion becomes audible when I put it into triode mode, particularly in the LF region.

I also included an adjustable feedback network, and can switch the feedback level on the fly. I find that lower feedback sounds better, but haven't tried zero feedback yet.

Anyway, it's really easy to add a switch so you can change between ultralinear / pentode / triode... why don't you just add such a switch to your circuit, and then you can tweak to your heart's content!

The EL84 is indeed a very well regarded tube, if you can make due with the lower power handling compared to the EL34... the only thing I don't have much experience listening to this type though... all I have is an old reel-to-reel which uses single EL84's in pentode mode to drive it's little wee internal speakers It does actually sound very good though!

If I had a choice today to build an amp based on either tube type, I'd go with the EL84, just because I find I don't need so much audio power anymore, and I have a nice little collection of williamson topology circuits as well as some parts which would lend themselves very well to a nice little 10W p-p EL84 design. Plus, I think the sound quality of the EL84 could well be a little better than the EL34...
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Old 28th August 2002, 09:39 AM   #3
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Default The EL84/SV83 is in vogue as a driver in pentode mode.

Do a search on Thorsten Loesch on the internet. He used an SV83/EL84 as driver for his 300B legacy amp.
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Old 28th August 2002, 10:27 AM   #4
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I'm in the process of building a single stage signle ended preamp using a choke loaded EL84. I'll post details as soon as i'm done

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