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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: Low Rp driver and Interstage question... posted by Palustris on July 22, 2009 at 15:39:24:
Check out this link:
I believe this same trick was used in the "Komuro 300B" amp and it
does work well! I'm using it on an 845. However, this circuit is PERFECT
for you!
1. Pick an operating point for the input tube as you'd normally do.
My schematic has a 76, but you can use a 6J5 or whatever pleases you.
The 76 doesnt use a bypass cap. This is intentional - it LOWERS the gain
to around 8. So, the net gain of this stage is 8 * 8 = 64.
2. The plate voltage of the input tube dictates the operating point
for the 6V6. Vg = Va(input tube) at idle. To bias the 6V6, choose
an operating point for the 6V6 with Vk = Vg + bias. Basically, all of
the op point charts for the 6V6 move up by Va(76). Once you know
your op point, you choose the cathode resistor for the 6V6 that raises
the current.
3. I found an operating point that very conveniently uses 4.7K,47K and 470
ohms to work the magic. Fortunately - these value work swimmingly well
with a 430VDC power supply - which is a very common power supply voltage,
if your using 720VCT power transformers and a 5AR4/diodes/Hg rectifiers.
4. Never operate the 6V6 without a driver tube plugged in. The driver tube
is part of the bias ckt!
-- Jim
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Follow Ups
- Check out how I drive an EP 3033-2 with Direct Coupled 6J5/6V6 - Jim Doyle 07/22/0920:53:34 07/22/09 (0)
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