music, guitars & other obsessions

Vacuum Tube Amp Worksheet by Chuck Doose

I got a bunch of worksheet off the Web to help me with designing amplifiers. I tried quite a few but so far I have to say the one written by Chuck is definitely by far the best one. The worksheet utilizes Excel’s Solver function to derive the loadline characteristics as well as provides an estimate on the THD generated by the amplifier. It is also unique amongst the worksheets in that it relies on tube’s SPICE model in its analysis. Whereas, all the other worksheets require the user to enter the plate curves data points manually, which is time consuming and prone to errors.

The gold standard of the tube amp design software is SE Amp CAD, it is a great software but also proprietary and it does not allow the user to add more tubes, so you are stuck with only the popular “audio type” of tubes, and those are usually expensive due to their popular nature.

One of the tube gurus, Steve Bench also has a few worksheets for plotting loadlines and distortion curves, and they are very good as well, but they require the user to manually input the plate curve data as mentioned above. I think they are the best alternatives for those that do not work with SPICE and are more used to working with plate curves with pen and tracing paper the old fashion way – not that there is anything wrong with that! In fact, a lot could be said for doing things manually, as it often provide more insight into the dynamic nature of the tube’s operation.

Anyway, to give Chuck’s worksheet a more finished look, I added a “Report” tab, so a printed report a la SE Amp CAD could be generated, an example is shown below for illustration.


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