Using Eagle for Tubes designs

[alexmoose]

Hello everybody!

no one wants to spend all that money on a full copy of Eagle. however I recently discovered that my university allows me to use a full copy of Eagle Pro from the computer lab. so I am really exited to make some PCBs for Tube projects. but I have a few questions on how to use it to make the best tube amp.

how do I know what kind of spaces to use for the PC mount tube sockets? does anyone have any pre-made that I could import?

do I have to be careful with auto routing functions because it is an analog device? how do I make the board Analog Safe?

any help would be wonderful!

-Moose

[pmillett]

I have a library that might help you get started posted on this page:

http://www.pmillett.com/diy_cad_programs.htm

I wouldn't do autorouting. It's sometimes OK for a digital board but not good for anything analog.

Routing an analog PCB is not much different than doing point-to-point wiring. Most of the same rules apply, about keeping signals short and direct, separated from each other. etc.

As far as high voltage goes, set the minimum spacing to something big, like 0.020" or 0.030". Then run DRC - it will show any violations.

Pete

[dsavitsk]

Pete's library is very useful. Tubelab has also posted a library that has some useful stuff. There are a couple of tube libraries that can be downloaded from the cadsoft site, but be aware that most tube sockets won't fit them -- this is especially the case for octals. With the novals you just need to make the holes in the pads larger, but in the octals you need to move them outward as well. It is worth picking up a few sockets to measure.

[tubelab.com]

Look on Eagles web site. The US version is :

www.cadsoftusa.com

in the download section, there is a "tubes" library.

This library contains symbols and packages for most of the popular 9 pin and octal tubes. Print them and make sure that they match your sockets. There are two different packages for most sockets, the alternate package is the one that I use.

I strongly advise against using the autorouter on any audio board. It is not smart enough to keep inputs and outputs away from each other. A vacuum tube circuit operates at higher impedances than usually found in PC board designs. You must think about what you are doing. For example, in many PC boards ground is routed on the reverse side of most signal traces for shielding. Due to the high impedances the extra capacitance that this creates will cause high frequency rolloff. The auto router will not do this.

If you can get PC boards made in school, experiment with a single stage amp, like a line stage. It will take a few "experiments" to learn what works and what doesn't.

I have been designing PC boards for over 40 years and it still takes me a few tries to get it perfect. The TubelabSE took 4 complete redesigns before I got it perfect. The SimpleSE took 2.

I wrote a long answer about PC board design in a previous thread a few months ago. You should be able to find it by searching.