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Old 7th March 2011, 10:36 PM   #1
tweakk is offline tweakk  United States
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Default EL84 driving EL84 SEP

I'm looking to try this for kicks.

Any thoughts?

http://home.comcast.net/~jafix/SakumaEL84.html
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Old 7th March 2011, 10:40 PM   #2
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What is the point in feedback shunted by 220 uF capacitor?
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Old 7th March 2011, 10:44 PM   #3
tweakk is offline tweakk  United States
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Don't know. I'm just a noob that builds what the schematic shows. That's why I brought this here to sort out the bugs before I try it.
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Old 7th March 2011, 10:48 PM   #4
spswmsw is offline spswmsw  Ukraine
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It works. I've built nearly the same once. Try it.
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Old 7th March 2011, 10:51 PM   #5
tweakk is offline tweakk  United States
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So how does it sound?

Any improvements to the circuit to recommend?
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Old 7th March 2011, 11:25 PM   #6
tinitus is offline tinitus  Europe
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how about UL PSE or PP output stage, with ccs cathode, or leds

may be worth to have a sneak peek on this one http://www.dhtrob.com/projecten/el84_6bw6_pp_4.shtml
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Old 7th March 2011, 11:35 PM   #7
spswmsw is offline spswmsw  Ukraine
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Quote:
Originally Posted by tweakk View Post
So how does it sound?

Any improvements to the circuit to recommend?
Clear and transparent, open sounding.

I've used for the driver tube
100R 2W triode strapping resistor
270R 5W cathode resistor bypassed with 100uf 50v cap
8K 10W anode load resistor
300 volts B2 voltage
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Old 7th March 2011, 11:57 PM   #8
tweakk is offline tweakk  United States
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Thanks "tin" what an interesting site!

"sp",

I'm sorry to say that I need a schematic to work off of and told specificly where things go although I know the basics of your recommendations. Thanka ya...

Last edited by tweakk; 8th March 2011 at 12:06 AM.
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Old 8th March 2011, 12:14 PM   #9
DF96 is offline DF96  England
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The basic premise of this circuit is false. A particular valve has a particular 'sound' at a particular point in a particular circuit carrying a particular signal at a particular bias point. Using the same valve twice does not mean that you get more of that sound.

In this case the input EL84 is used in triode mode at one bias, while the output is run as a pentode with a different bias. The signal in the first valve will be much smaller than in the second valve.

In addition, the circuit has some shortcomings. The first stage has a grid stopper, but not the second stage where it is more likely to be useful. The first stage relies on the volume pot wiper staying in contact with the track. Better to have a coupling capacitor and a grid leak resistor. Finally, as other have said, the feedback goes to a decoupled point so will have no effect except possibly to create infrasonic instability.

The website is full of fine sounding words, but a poor design based on a misunderstanding.
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Old 8th March 2011, 01:10 PM   #10
tweakk is offline tweakk  United States
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Seems like you're in a bad mood DF.

Where does the guy get unreasonable with "fine sounding words". He just sensibly offers the concept, advises researching the origin and then states:

"I'm not looking for anything quite so exotic - I'd be happy with a clean 3-5 watts per channel from a fairly straightforward and simple circuit that utilizes commonly available and widely manufactured valves."

Your fixes to the circuit are noted but minor are they not? When I build this I'll try it your way. BTW the feedback doesn't go anywhere because none is implemented in the final design.

As far as the EL84 sound not adding together I'll bet it's a lot closer than using different tubes. Besides the EL84 is not too shabby as a driver and output tube so why not?

What you seem to be missing from the original article and this thread is the fun factor.

Lighten up brother...

Last edited by tweakk; 8th March 2011 at 01:15 PM.
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