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Old 7th December 2012, 04:00 PM   #11
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That is a great idea. the first stage realy is the "push" for the second stage. I am totaly okay with using solid state parts smartly.
At this point however I have the 12ax7 working and I'm liking it!
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Old 7th December 2012, 04:48 PM   #12
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Here are schematics to this point.
Attached Images
File Type: jpg 12faq8 exp.jpg (402.2 KB, 37 views)
File Type: jpg 12faq8 exp 2.jpg (168.7 KB, 37 views)
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Old 10th December 2012, 04:04 PM   #13
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I Need To Make Note of a Couple Corrections to the Schematic.

On the "shift" switch the top switch contact should only be connected to the 10k resistor, there should be no connection to ground.
Also my brother pointed out that I left off values for the bias pot and cap. That pot was 25k and the cap is 100uf 50v.
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Old 10th December 2012, 06:00 PM   #14
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I'm also a newby to tubes, and I've also thought about paralleling the sections of small-signal triodes for more current. But in theory I imagine each section probably should each have some independence in their B+ resistors and grid resistors too, pretty much like paralleled output tubes. Otherwise, for one thing, their internal capacitances add up and they start limiting bandwidth as the high end gets cut off (perhaps even worse due to miller effect?). And in reality I wonder whether they just get more noise and wonder what I need more current for, unless I was trying to drive more output tubes or something like that.
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Old 10th December 2012, 10:01 PM   #15
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Well in this case my reason for running them in parallel was because they seemed incapable of have two different signal operating internaly. ossilations like when sensitive inputs get too close to strong output signals. That may have been because I came to this conclusion early in my "playing" phase. It is possible that now with some of the adjustments I have made to the plate resistors and cathode sections it might work. Now I have a much smaller plate resistor than I did originaly. As far as the effects of running them parallel. I notice no real loss of frequency response, at least any I care about. Matchless amplifiers run lots of their amps with 12ax7 in parallel and they sound awesome. From what I understand there is little to no increase in gain but lessnoise and better frequency response in that arrangement. those are definite reasons in my book. I also think that in the case of something like a tone stack following the stage, the paralled tube stage might "push" it better. I also in some ways are a newbie. I get some of the theory, but have a long way to go. I have built, modified and repaired several amps and the bottom line always is not theory but how it sounds. That by no way means I don't care about it. I have a genuine quest to figure out as much as I can. I find understanding the theory and seeing it in action super cool.
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Old 10th December 2012, 10:23 PM   #16
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What amps are you thinking of where a paralleled output tube uses seperate plate resistors, usualy isn't it the output transformer? lots of cathode biased amps use a single cathode resistor.
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