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Topics - nodz

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Tubes and Hybrids / Parallel Push Pull amplifiers
« on: May 06, 2013, 06:29:52 PM »
I was wondering if anyone could help me.  I have a question regarding drawing load lines for biasing  of tubes in an amplifier when there are four tubes in parallel, e.g a fender 100 watt amp.
If two tubes have a plate to plate resistance of 10k ohm and we have an OPT with a primary of 10k, then the load line that we need to draw on the tube/plate characteristics curve is 1/4 of this, or 2500 ohms.  If using 250V at plate, load line should pass through the points  250V, 0ma and 0V, 100mA.  Now if we add a second pair of tubes.  If using the same 10K primary OPT, should a 1250 ohm load line now be used, passing through 250V, 0mA  and 0V, 200mA?

The Newcomer's Forum / Newcomer, Melbourne, Australia
« on: March 22, 2013, 04:42:53 PM »
Just thought it was time to introduce myself.
My name is Chris but everyone calls me Nodz.
Been lurking around various guitar/amp and hifi/diy audio forums for a while.
Have four guitars (3 electrics and one acoustic) and two SS practice amps.
Have made some SS and valve audio equipment, thought is was about time I started skimming around the net and try and design my own guitar amp.
So after a bit of reading, designing, redesigning, borrowing circuits from others I've come up with the attached.
Due to constraints both time and financial, will probably build amp in modular fashion, that is step 1) preamp, 2) stand alone reverb 3) then the PA. 
Possibly will include an overdrive section but the idea is to have an organic modular amplifier, that can be altered as I go along so if I don't like certain developments, I can revert back to the previous state if desired.
I also haven't decided on the final PA.  At the moment, it uses a couple of PP 12AQ5 (just because that's what I found in my junk box) but I may use LM3875 and have 2 x 50W output channels, 2 x 6L6 (50W) or 4 x 6L6 (100W).  I just haven't established what kind of O/P I require yet.

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