EL84 SE advice'n'schematics needed - diyAudio
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Old 20th September 2005, 07:28 AM   #1
hates ground loops
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Default EL84 SE advice'n'schematics needed

Hi there,

I am looking for some schematics of an EL84 Single Ended amp.

If possible, without capacitors (or as few as possible) in the signal-path. Something really simple, like EABC80/EL84 or some ECC.../EL84 combo or, hopefully, something I haven't heard of yet.
I know, EL84 is not that exciting, but good to begin with...

Thanks, David
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Old 20th September 2005, 11:46 AM   #2
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Old 20th September 2005, 12:59 PM   #3
amperex is offline amperex  United States
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Default RH design looks great

Suggested tweaks:

Change that EL84 cathode cap from electrolytic to either a motor run oil cap or a Solen polyproplyene. Same on the 10uF @ 350 v cap- polyproplyene. Change the 220uF filter cap to a pair of 100uF ARC oil cap (inexpensive on ePay). I can not impress enough the difference in sonics leaving electrolytics out of the circuit except for that capacitor at the rectifier.

Use the stellar sounding GE EL84 grey oval plate as it outperforms every EL84 I auditioned in my few amps plus a few owned by other audiophiles- all agreed, they kept the GE EL84 everytime.

I never heard a good sounding 12AT7 tube, it is a VHF/UHF RF amp tube used in older TV tuners, etc. Change that tube to a GE 5751 black plate or a RCA Command 5751 black plate. Change the 10K resistor at the B+ feed point to 22K, change the 22K plate resistor to 100K & the cathode resistor to 1700 ohm. The 12AX7 'family of tubes' allows plenty of NOS variations for tuning the sonics.

I used about every rectifier tube ever manufactured in quite a few different designs. Bump the transformer up to a range of 620VCT to 640 VCT & use a Sylvania 5R4GYB- inexpensive & plentiful. Even a Mullard 5AR4 or WE274 has nothing over the Sylvania sonically & a good rectifier tube makes for quite a difference in sonics.

The best coupling cap are Russian teflon. Parallel to get to .2uF or use nothing of less quality than AuriCap. AuriCap take about 200 hours to break-in.

I see no reason for two filament windings. Just bypass with a .1uF polyester type at the 12AX7 filament wires to ground.

My 2 cents.

edit= spelling error
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Old 20th September 2005, 01:30 PM   #4
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Did ya Google or try forum search?

I think everyone and their cat has made an EL84 SE at one time or another
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Old 20th September 2005, 01:45 PM   #5
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Default Re: RH design looks great

Hi Amperex,

Quote:
Change that tube to a GE 5751 black plate or a RCA Command 5751 black plate. Change the 10K resistor at the B+ feed point to 22K, change the 22K plate resistor to 100K & the cathode resistor to 1700 ohm. The 12AX7 'family of tubes' allows plenty of NOS variations for tuning the sonics.
You are aware that this circuit uses shunt FB from the output stage plate? If so, you surely did the math and thus you know what load the poor 12AX7 (or its variants) will have to face

Yes, there is a reason why Mr. Kitic did chose the much higher gm 12AT7 at that place, indeed.

Tom
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Old 20th September 2005, 02:36 PM   #6
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Mine is pretty simple - second amp on my page. I used a toroid isolation transformer and added my own filament winding. Use a full wave bridge with 240V, doubler with 120V. There's no hum with 470 uF caps in the doubler, but it would need another stage of filtering for UL or triode wiring... My audio page
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Old 20th September 2005, 03:19 PM   #7
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RH84

Build this amp. You will not regret. Simple and Cheap. Nice sounding, very high end. I play it with my Audio Note system. Thanks to Mr Kitic!
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Old 20th September 2005, 03:34 PM   #8
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Hi,

no capacitors in the signal path? That is my speciality! :-)

Maybe want to try this, I built it only yesterday (as a preamp):

Click the image to open in full size.

If you're feeling groovy you can build it without electrolytics. It should be good for about 1.5 pure triode class A watts. Be sure to use a tube rectified power supply with CLCLC filtering. I recommend the EZ80 for this. You will be surprised how far those 1.5W will get you even on normal speakers!

Happy building
Michael
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Old 20th September 2005, 03:37 PM   #9
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The RH84 looks awesome. That's the thing I've been looking for.
I done Google and the forum, but most EL84 Amps end up to be PP or "stuffed" with caps. After the Zenlite I want something as simple with tubes and as little caps as can be. Especially in the signal-path.

This thing will be small and beautiful. Thank you very much.

Dave
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Old 20th September 2005, 03:46 PM   #10
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Wow, tubemaster, that thing looks awesome too, meine Fresse.

I think I wanna build em both.
The caps are all polypropylene and µ Farad, right? These must be big and expensive...
What exactly is meant with "4-5K" right above the Ausgangsübertrager?

Danke, Dave
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