Re: Yet another LA-2A build log
« Reply #20 on: April 30, 2011, 11:13:38 AM »
Wow - looks great!   

I love your faceplate design - you did that all in diy-layout-creator?

I was also intrigued by your point-to-point methods; you make it look so easy that even a noob like me could do it.   :D

Nice work.


Paul Fawcett

Re: Yet another LA-2A build log
« Reply #21 on: April 30, 2011, 06:21:34 PM »
Wow - looks great!   

I love your faceplate design - you did that all in diy-layout-creator?

I was also intrigued by your point-to-point methods; you make it look so easy that even a noob like me could do it.   :D

Nice work.


Thanks for the kind words! I've just finished the wiring, and have posted a slew of pictures to the blog: http://wombatamps.blogspot.com/

I did all of the circuit board layouts with the latest version of DIY layout creator, which I highly recommend.. Version 3 is much faster, morestable, and feature complete than any of the previous versions: http://code.google.com/p/diy-layout-creator/.  I work hard on the layouts, and really try to use a "tube socket-centric" approach so that all the critical runs are nice and short, and that each triode is has its accompanying circuitry very close by, including the cap that feeds that PSU node. It also makes it easier to do a good job on the ground scheme. It's served me well with high-gain guitar amps where oscillation problems and noise are ever-lurking if you bozo the layout.

The faceplate, however, was just done in a vector drawing program. I used Canvas, but almost anything would have served - CorelDraw, Adobe Illustrator, Inkscape, etc.

Cheers,

Paul

Paul Fawcett

Re: Yet another LA-2A build log
« Reply #22 on: May 02, 2011, 11:18:25 PM »
Well, there had to be one fly in the ointment. Turns out I misread the 12BH7 data sheet, and ended up thinking it was a 300mA heater instead of a 600mA heater, so ended up with a DC heater voltage regulator that wasn't quite beefy enough for the job.  No huge problem though, as I ended up just running the pentode heater on AC from the unused 6.3V tap on the PT and all is well.  I did learn a valuable lesson along the way too of the necessity of taking into account the cold-state turn on-current of the heaters....turns out also that it's quite possible to have a total nominal working heater current within the spec of the regulator, but still have it not regulate because the cold-state current is high enough that it drives the regulator far enough into over-current shut down that the heaters stay "behind the curve" and never get sufficiently warm to lower demand and climb out of current limiting and back into the regulated area of operation.  With the particular 1.5A regulator I used, I found that anything above about 1.3A nominal load wouldn't "trigger" in a reasonable time frame.

  Voltages now seem reasonable throughout the amp - just need to get it into the studio now for testing....


 

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