Rahul, You can't use the internal tuner because the amplifier input
impedance varies with drive level and the auto tuner tries to follow that. It
is
too slow for that kind of use.
The radio senses the higher vswr and reduces the drive power which
increases the impedance and so on..
A manually adjusted tuner will work much better in this application. In
fact, the amplifier input matching device is supposed to do this very job but
the Q of the tuned circuits is too low for modern solid state radios as it
was designed 40 to 50 years ago when radios were tube type.
A small manual tuner will provide the needed Q boost to allow the radio to
deliver full power to the amplifier.
73,
Gerald K5GW
In a message dated 9/8/2009 12:29:36 P.M. Central Daylight Time,
vu3raz@gmail.com writes:
Yes I tried that Gerald, the internal tuner eases the SWR and improve
drive, still no luck beyond ~ 400 mA with 2 tubes on 20.
Regards /// Rahul
On Tue, Sep 8, 2009 at 10:51 PM, <_TexasRF@aol.com_
(mailto:TexasRF@aol.com) > wrote:
If you have a small antenna tuner, it can be used to reduce the vswr for
test purposes.
73,
Gerald K5GW
In a message dated 9/8/2009 11:59:00 A.M. Central Daylight Time,
_vu3raz@gmail.com_ (mailto:vu3raz@gmail.com) writes:
I will try that tomorrow don. For the input circuit does nothing on 14 MHz
VSWR is nowhere near 2.
I am thinking of ripping the input tuned circuit and replacing it with a
simple parallel resonant ckt as in the eimac design.
Rahul
On Tue, Sep 8, 2009 at 9:59 PM, Paul Playford <_paul@w8aef.com_
(mailto:paul@w8aef.com) > wrote:
> Richard Measures, AG6K, has done a lot of work on SB-220s and talks about
> the input circuit at:
>
> _http://www.somis.org/SB220ci.html_ (http://www.somis.org/SB220ci.html)
>
> FWIW, Richard has his detractors however I have applied his
modifications
> to several SB-220s and a Henry 2K with great success.
>
> de Paul, W8AEF
>
> ZF2JI/ZF2TA FO8DX/FO8PLA 8Q7AA XZ0A VU7RG TX5D
>
> ----- Original Message ----- From: "Rahul Sathe" <_vu3raz@gmail.com_
(mailto:vu3raz@gmail.com) >
> To: <_amps@contesting.com_ (mailto:amps@contesting.com) >
> Sent: Tuesday, September 08, 2009 8:32 AM
> Subject: [Amps] SB221 Low Power Help
>
>
>
> Hello Experts,
>>
>> My name is Rahul call VU3RAZ. This is my first post to the list. I am
>> seeking help on fixing my old SB221.
>>
>> as such the amp works on all bands, no arc or parastatics, tuning and
>> loading is smooth and easy.. I am not able to load the amp to full rated
>> plate current even with a 100 W drive with my 756 Pro3. Input VSWR is
>> high,
>> I tried tuning the input tuned circuit but no luck on few bands (20,
15).
>> With the 756 ATU the things improve but I can not get plate current
beyond
>> ~
>> 400 mA. Even tried disconnecting HT from each tube to see if one if the
>> 3-500 is dead... both work but even with single tube I am not able to
load
>> the amp fully. Am I looking at dead (weak) tubes ... can both of them
show
>> exact same behavior? Or I am missing something I am not sure if I need
to
>> re
>> build the PSU (replace caps)
>>
>> Please help...
>>
>> 73
>> DE VU3RAZ
>>
>>
_______________________________________________
Amps mailing list
_Amps@contesting.com_ (mailto:Amps@contesting.com)
_http://lists.contesting.com/mailman/listinfo/amps_
(http://lists.contesting.com/mailman/listinfo/amps)
____________________________________
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|