Re: KPA-1500 on digital modes
Posted by
N4ZR on
Sep 01, 2019; 8:44pm
URL: http://elecraft.85.s1.nabble.com/KPA-1500-on-digital-modes-tp7654828p7654921.html
FWIW, one of the things I like best about my KPA-1500 is that you can
use its antenna tuner with the amp on Standby
73, Pete N4ZR
Check out the Reverse Beacon Network
at <
http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.
On 9/1/2019 4:02 PM, K9MA wrote:
>
>> On 8/31/2019 6:02 PM, Roger D Johnson wrote:
>>
>>>
>>> Isn't this exactly the way some of the first ham linears were designed
>>> for an input of 2000 watts in SSB and 1000 watts in CW? There
>>> was a switch on the front panel for SSB/CW mode which dropped
>>> the plate voltage for CW mode so that the tubes saw the same
>>> load impedance they did in SSB mode thereby keeping the efficiency
>>> high and not requiring retuning between modes.
>
> I think it was more to make it harder to exceed 1 kW input on CW. It
> is almost always possible to load an amplifier (with the usual PI
> network) for efficient operation at less than maximum output. It just
> has to be loaded lightly and not driven too hard. That conflicts,
> however, with the usual procedure of loading for maximum output. Also,
> with two plate voltage settings you could usually tune for maximum
> output at the low setting at about 1 kW input, and it would be tuned
> about right for 2 kW at the high setting. This reduced the stress
> during tuning, and probably was the most common strictly legal way to
> tune for 2 kW PEP input in those days.
>
> Actually, legally tuning for 2 kW input in those days was tricky.
> Collins used a bridge which compared RF input and output voltages and
> allowed tuning at low power. I used that circuit in an amplifier I
> built about 50 years ago, and it worked pretty well.
>
> A PI network in a tube amplifier allows properly loading the amplifier
> into a range of load impedances, but the operator or autotuner is
> looking at grid current, plate current, input/output voltage ratios,
> etc. to get the tuning right. This sets the tuning for efficient,
> linear operation. A solid state amplifier and ATU work very
> differently. The amplifier is designed to operate properly into a 50
> Ohm resistive load, and the job of the ATU is to make the actual load
> as close to that as possible. One result of that is that a rather
> small mismatch can have a large effect on efficiency and/or linearity.
>
>
> 73,
>
> Scott K9MA
>
______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.htmlMessage delivered to
[hidden email]