[Amps] Acceptable Swr for a tube amp without retuning.

[Jim Brown]

On 2/6/2025 6:07 PM, Lukasz wrote:
> So could someone please explain or point me towards some books/articles
> that talk about what happens exactly with voltages/currents at bad SWR?

What you need to study is "Transmission Lines."  If you are comfortable 
in English, the ARRL Handbook and something like that from RSGB are good.

The ARRL Antenna Book goes deeper, and comes with a very nice (but very 
simple) app that computes SWR, loss, voltage and current along the line, 
and graphs voltage and current. The app is TLW. It's a very nice 
learning tool.

There's also TLDetails, a simple free Windows app by AC6LA, that 
computes loss, SWR, and complex impedance at one end of a line for 
complex impedance entered for the other end. It computes and plots the 
variation of Zo, loss, and velocity factor with frequency.

https://www.ac6la.com/tldetails1.html

AC6LA also published ZPlots, a freeware Excel spreadsheet which does 
that and more. It runs ONLY in Microsoft Excel, not in clone 
spreadsheets. One of its most useful tools is the ability to compute the 
fundamental properties of some unknown transmission line from swept 
impedance measurements of a known length.

https://www.ac6la.com/zplots1.html

Nearly all texts for radio uses of Transmission Lines treat Zo and VF as 
constants for all frequencies, but they're not. To understand why, and 
how they vary with frequency, study my tutorial about that.

http://k9yc.com/TransLines-LowFreq.pdf

And this Q & A about Transmission Lines and stubs, which is why we need 
"big" transmission line for low loss.

73, Jim K9YC