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Old 30th December 2002, 03:26 PM   #1
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Default Tentative EL84 SE Design.

Hello all,

Sitting around the shop bored so I threw this design together using data sheets. Anyone see any problems or have any suggestions for improvements? I was thinking about using a 12AT7 instead of the 12AX7. Thanks for looking.

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Old 30th December 2002, 03:33 PM   #2
Joel is offline Joel  United States
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a) 8.2k is too small a load for the 12AX. Make it 100k.
b) Put a resistor inbetween the B+ output tran tap and the 50uF cap. 1,000 ohms is good.
c) Seperate 250 ohm cathode resistors for each tube.

Hmmm.... make those changes and you'll have my amp!
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Old 30th December 2002, 03:34 PM   #3
Joel is offline Joel  United States
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d) add a 100 ohm, 5W resistor inbetween screen and plate. It's to limit current flow for safety.
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Old 30th December 2002, 03:51 PM   #4
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Default THE ALFABET.

Hi,

e)better still,use a separate supply for in- and output tubes.

f)better still,regulate the anode supplies for both tubes.

g)better still,up the anode supply for the 12AX7A to at least 300VDC

h)hey,and what about a volpot at the input?

Okay you got 18 characters left...

Cheers,
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Old 30th December 2002, 04:02 PM   #5
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g)
Quote:
add a 100 ohm, 5W resistor inbetween screen and plate
Then it won't be triode.
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Old 30th December 2002, 04:05 PM   #6
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Default HOLD ON...

John??

g) was used already.

h) as well.

i)Joel suggested that already.

j)pseudo triode is a better word IMO.

Ciao,
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Old 30th December 2002, 04:08 PM   #7
dhaen is offline dhaen  Europe
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Quote:
g) was used already.
Well it was a quote
Damn, I must have started up in modulo 7 this morning
z)
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Old 30th December 2002, 04:12 PM   #8
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I don't really want to run this in triode mode if it will stop me from getting 4 watts or so out of the circuit into an 8 ohm load.

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Old 30th December 2002, 04:15 PM   #9
dhaen is offline dhaen  Europe
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Quote:
I don't really want to run this in triode mode
Well it's drawn in triode mode.
If you want pentode mode, you'll need some NFB to make it sound reasonable IMO.
What is the impedance of the iron?
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Old 30th December 2002, 04:16 PM   #10
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Joel, did you mean use a separate 150 ohm resistor for each EL84 cathode?

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