Re: [Amps] New Guy, Old 813 amp

["Tom W8JI" <w8ji@w8ji.com>]

>I cannot remember the company that makes it, but there is a 
>small autotuner
> designed to be retrofitted into a 6M-HF amplifier that 
> sells for $100.00 that
> would fit the bill.

The problem with autotuners are::

1.) The impedance of a tube is dynamic. It changes with 
drive level and even the output tuning. As such autotuners 
tend to "hunt" and never settle correctly.

2.) The cathode or grid of an amplifier has harmonics. This 
requires a low impedance reflected at the tube element to 
reduce IMD and improve efficiency

A person is much better off with a properly designed network 
that provides a low impedance **at the tube** for harmonics!

73 Tom 


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