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In Reply to: Dan, why on earth recommend a circuit that... posted by Allen Wright on March 27, 2007 at 01:03:03:
AllenCalico was looking for a preamp
with ~30 gain and no transformer.
This was the ONLY one that I know of.
So I proposed it to Calico -
gain of about 35 and 200 Zo.DanL
Follow Ups:
Nice circuit, but Allen is Right (pardon the pun), you'll need to get rid of the shielded hookup between the attenuator and the grid. So layout will be important for low noise.Also- the grid input needs a grid stop resistor (about 1-5K) as close to the tube as possible! I would also recommend playing with the 680 ohm cathode resistor- offhand given a mu of 35 the value seems a little low, but OTOH a lot depends on the semiconductor plate load. If it were me, there would be no way I would allow the semiconductor devices into the circuit....
That semiconductor or any semiconductor?Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
for plate loads and the like I prefer a good resistor, but I have no problem using semiconductors for regulation if they are properly designed.
This design is not mine - just one I saw.
I have never used this design nor plan to.
My 12B4 is quite fine for me 8^D
Here is the site I got it from:http://www.cognitivevent.com/av_foreplay2.html
DanL
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