On Mon, 21 Dec 1998 14:23:29 +0200 Ian Roberts <itr@nanoteq.co.za>
writes:
>
>
>
>John Fielding wrote:
>
>>
>> As far as the other aspect of the argument regarding the linearity
>versus
>> anode voltage - it is a well documented fact that the greater the
>anode
>> supply available the more linear the operation will be for a given
>output
>> power. Why else do we use such high voltages if we could use lower
>and
>> safer voltages? Look again at the formula - here you can plainly
>see that
>> the predominant factor in obtaining high output power is the voltage
>term!
>>
>
>This is not peculiar to tubes.
>And is why the ICOM IC-781 running the PA transistors at 28 V achieves
>37 dB
>IMD, compared to the typical 24-28 dB from 13 V transistors (IC-565,
>476, Yeasu
>847, 920, etc). 50 V transistors are even better, but as long as hams
>use 13 V,
>we will have to continue enjoying 40 kHz-wide SSB signals, as
>generated by a
>nearby 400 W 13 volt USA-made linear on 6m.
A big part of that 6M linear problem if it is a TE as I suspect, is that
it uses a horrible bias circuit that goes into class C at around 100W
output. Switching over to an active bias will do wonders.
All it takes is 2 transistors and a few caps/resistors. I've converted
several of them.
73 Carl KM1H
>
>Ian, ZS6BTE
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|