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L'Amp: A simple SIT Amp
L'Amp: A simple SIT Amp
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Old 20th December 2011, 12:07 PM   #81
juanitox is offline juanitox  France
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i have also received my 2Sk82 , and the BIIIIG 300w 120 sylvania bulb , i don't know yet if i will use them or a big power resistor as my chassis is not very large. i will begin the build this week and i'll tell you if this DIY is really Idiot proof
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Old 20th December 2011, 03:50 PM   #82
Michael Rothacher is offline Michael Rothacher  United States
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L'Amp: A simple SIT Amp
Figure 11 is pretty straight forward.

With figure 10, the thing that could be tricky is remembering that the gate bias is negative. If you let it go too positive, Id goes up, and eventually it goes poof.

I tested all my power supplies out of circuit first. Then, I adjusted the bias supply for -12V, powered up the circuit, and adjusted the pot so I had around 13.4V from Drain to Source.
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Old 20th December 2011, 07:36 PM   #83
Tea-Bag is offline Tea-Bag  United States
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L'Amp: A simple SIT Amp
Quote:
Originally Posted by Michael Rothacher View Post
Figure 11 is pretty straight forward.

With figure 10, the thing that could be tricky is remembering that the gate bias is negative. If you let it go too positive, Id goes up, and eventually it goes poof.

I tested all my power supplies out of circuit first. Then, I adjusted the bias supply for -12V, powered up the circuit, and adjusted the pot so I had around 13.4V from Drain to Source.
Michael,
Are you saying turn -12v on first?
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Old 20th December 2011, 07:50 PM   #84
Michael Rothacher is offline Michael Rothacher  United States
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L'Amp: A simple SIT Amp
I just verify that the pot is at the full -12V position and not the other way around before I turn it on for the first time.
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Old 20th December 2011, 08:13 PM   #85
Roscoe Primrose is offline Roscoe Primrose  United States
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You may want to look at your time constants in the PS filters, to make sure that the -12V supply doesn't come up significantly slower than the B+ as well....

Roscoe

Last edited by Roscoe Primrose; 20th December 2011 at 08:13 PM. Reason: typo
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Old 20th December 2011, 08:31 PM   #86
Michael Rothacher is offline Michael Rothacher  United States
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L'Amp: A simple SIT Amp
If one uses the schematic I provided in my first post, this is not an issue.

If you build something else or use significantly different capacitor values, then Roscoe's caveat applies
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Old 21st December 2011, 07:01 PM   #87
juanitox is offline juanitox  France
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thanks michael ,i will stay with Fig11 with just the option 47000uf bypass cap on R1 i'm a tube man
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Old 21st December 2011, 07:57 PM   #88
Michael Rothacher is offline Michael Rothacher  United States
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L'Amp: A simple SIT Amp
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thanks michael ,i will stay with Fig11 with just the option 47000uf bypass cap on R1 i'm a tube man
So, you got some KD-33 then?

Also, I think you mean R3.
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Old 21st December 2011, 08:06 PM   #89
Roscoe Primrose is offline Roscoe Primrose  United States
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R1, 1R resistor, details, details
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Old 22nd December 2011, 01:00 PM   #90
triode_al is offline triode_al  Netherlands
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Quote:
Originally Posted by jkchoi View Post
How about this?

Will it work?
Hi Choi,
Because it is two N-devices, the two drive voltages to the grid have to be referenced to the drain. What I once did was use a transformer coupling to both output devices (1/2+2, so two similar output windings), attached a proper bias, set the current, and presto, very nice sound, extremely high drivability too.
The traditional way is to use a bootstrap in the upper side (see e.g. the BA2).
albert
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