Phil,
You hit on a key point here with the Q. I also beleive the high-Q issue
is possibly overrated.
I realize the theoritical benefit to the higher Q. But the losses
associated with high circulating currents are real as are the voltages.
A lower Q amp is easier to tune, and easier to stock with components.
And the power output will probably be higher at a lower Q.
My initial tank was setup with a Q=12 target. But after having a lot of
problems with the thing, and seeing a comment from Orr about Q as low as
8, I changed it and never went back. Night and day improvement in
stability and ease of use.
I had measured the 3rd order IMD and 2/3 order harmonics and could not
find any detectable change (within my resolution ability of about
+/-1db) with either tank. That lead me to beleive that in my case
anyway, the signal purity benefits associated with a higher Q were
mitigated by other factors - probably in the construction of the amp
given the very limited space available.
73/jeff/ac0c
Phil Clements wrote:
> Subject: Re: [Amps] RL Calculations
>
>> Plus, if the Q strays a little from the current favored 12, who cares.
>>
>> Bob W6TR
>>
>
> I am so glad that when I built my 3X3 single-band (160 meter) amp I used a
> 20 uh tank coil as L1 in a pi-l configuration. This came out to be a Q of 6.
>
> For over 15 years, I take a few hours in October to clean and lube the amp.,
> and then tune it up on 1825 KHz. I never touch the thing again until the
> next October. The lower Q allows QSY'ing +/- 15 KHz without having to fiddle
> with the knobs. My other amp is a Harris RF-110, which has no tuning
> controls at all!
>
> (((73)))
> Phil, K5PC
>
>
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