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Old 15th February 2006, 03:07 PM   #1
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Default SE EL84 amplifier schematics

Hi again everyone,
Just wanting to see if any of you have any suggestions for a good SE EL84 amplifier to build, I am going to salvage output and power transformers and valves from my old heathkit S-33 and Rebuild it in a new chassis, But i have been thinkign mabey i shouldnt stick to the circuit they used and mabey i can build somethign different, possibly even with some diffrent driver tubes.
Many thanks,
OWen
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Old 15th February 2006, 05:38 PM   #2
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mabey something like this?

I like the look of this because it is fairly simple, i could probably wire it all point to point useing just the component leads and keep it fairly small.
What sort of output power would this give out?
Would it work ok? any improvements that could be made? Or should i go for somethign completely different? if so any suggestions what i should go for?

Many thanks,
Owen
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Old 15th February 2006, 05:58 PM   #3
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Power would be ~5W, its an ultralinear S.E.

There have been many threads about EL84 circuits. Do a search and you should find many opinions.

I personnally think the RH84 is the best of the EL84 circuits that I have
heard but thats just my opinion.

RH84

Andrew
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Old 15th February 2006, 06:04 PM   #4
chrisvw is offline chrisvw  South Africa
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Default Bonavolta site

Have you seen these schematics?

http://www.bonavolta.ch/hobby/en/audio/el84.htm
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Old 15th February 2006, 06:08 PM   #5
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the output transformers i salvaged have three wires on primary side though, one too pin 7 and one too pin 9 and one too b+, not sure how i would go about wireing them up for that circuit? or would it simply be that i wire it up the same but instead of wireing the sacond wire to the el84 i put the resistor to that pin (pin 9 i think) and to B+ like ont the schematic.. and ignore the third wire ont he output tranny?
Looks good though, i might try it out and see what it sounds like, if i dont liek it it is no big deal i guess, there dont appear to be many differances between the different schematics i have found so cant be that hard to switch between them till i find one i like..
OWen
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Old 15th February 2006, 06:11 PM   #6
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thanks for the link chrisvw, i hadn't seen those schematics. might be worth a try aswell..
I guess i should start workign on the chassis!
Many thanks
OWen
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Old 15th February 2006, 09:02 PM   #7
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Hi Owen,

Here is another EL84 schematic called the "Minute" from SAC Thailand, the makers of SILK transformers.
I think the output transformer that they are using has a 5k impedance.

Good Luck

Norris

http://www.sacthailand.com/AmpMinuteEL84.html
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Old 15th February 2006, 09:14 PM   #8
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Norris Wilson:
That schematic looks pretty interesting, might give it a go first if i can find out about my output transformers.

Anyone:
How would i go abotu measureing my output transformers impedance? :S And what do i do about the fact they have three wires ont he primary side and most of the schematics only have two? :S

Many thanks,
Owen
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Old 15th February 2006, 09:32 PM   #9
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Also, in the amp that Norris Wilson posted, would it be easy to substitute the 6072A for something like an ECC82 or ECC88's or a pair of triode strapped 6AU6's or EF184's? just a thought i had as i have lots of these valves here but no 6072A's
Owen
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Old 15th February 2006, 09:39 PM   #10
billr is offline billr  New Zealand
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The cct for the silk transformer amp is nothing too special, it is missing an earth connection at the junction of the two cathode resistors though.

As for measuring the impedance of the transformer, the easiest way to do it is to apply an ac voltage to the primary, and measure the voltage across the secondary.

Voltage ratio can then be determined, square that and you have the impedance ratio. So if the tranny is designed for an 8 ohm output, multiply the ratio by 8 and et voila, you have the primary impedance.

hope that this helps.

kind regards

bill
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