This is a multi-part message in MIME format.
------=_NextPart_000_01BDFEA7.5ACB2C20
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Hi all - let's start a new discussion topic. I am generally considered a
reliable source of info but I have to admit that my experience on hf is
limited. Well to the question and I would like all to consider this one.
I will only have the time and money to build one hf amplifier and would
like constructive inputs for the initial thoughts I have.
Power supply I can happily tackle but the rf deck is the trickiest.
I have the following parts already.
Tube - Mullard / Philips QY5-3000A (tetrode - don't get confused by the 5
in the part number) plate dissipation 3000W. Fmax = 220 MHz and rated for
SSB operation. (Was used for tv ultra-linear duty on band 3 170 - 220
MHz in the UK). Vmax = 5kV and g2max = 1kV. Mullard data gives an output
of 1,5kW at 30 MHz ssb duty with IMD typically 33 to 42 dB. Plus, I have
the base and g2 decoupling gear from an old tv broadcast transmitter.
Other tube specs I can post if needed.
Tank inductor - big (about 4" dia and 12" long) probably suitable for the
low bands. Others I can wind from 1/4" copper tube which I have on hand.
Various variable capacitors - none really suitable for the anode tuning but
probably OK for load capacitor duty. Best one about 250pF with approx. 6kV
rating - tested at 8kV dc.
Several high power vacuum relays - about 10kV is the highest rating.
Lots of high voltage / current rf fixed capacitors.
Suitable blower - blows the QSL cards off the wall at 10 feet and frightens
the dog!
Now - why can't I build the tank circuit using the vacuum relays to
switch in fixed capacitors for each band. I have enough relays for this if
one uses 160m, 80m, 40m, 20m, 15m and 10m. (My transceiver doesn't have
the new WARC bands so I don't need to include them initially). Using a
relatively small vacuum variable for the anode tuning and eliminating the
normal tank circuit band-switch seems to me to be the way to go, in view of
the problems some amplifiers suffer from.
Overall physical size doesn't really matter. (The power supply will be a
separate item for versatility). I can have the required metal-work
fabricated locally by a craftsman I know. (Rather have enough room to make
the thing work efficiently than try and jam it all into a box which happens
to be available). I plan to pressurise the anode compartment and use a
scheme similar to the K2RIW design for 432 MHz with a chimney for the
exhaust.
Basic spec. At least 1kW out on ssb or cw - with no strain.
Yes - We should shortly get a 1kW licence class here. (I have just
finished writing the new regulations for the R.A. and part of the regs
covers IMD and not running an amplifier at it's limit and removing the
silly existing regulation which makes it an offence to own an amplifier
capable of more than 400W! - so big amplifiers will become the order of
the day).
Finally - If possible, the amplifier should also operate on 6m with similar
output.
Anyway, is there a flaw I haven't spotted. Come on guys what have I
missed. All ideas considered.
John ZS5JF
------=_NextPart_000_01BDFEA7.5ACB2C20
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
<html><head></head><BODY bgcolor=3D"#FFFFFF"><p><font size=3D2 =
color=3D"#000000" face=3D"Arial">Hi all - let's start a new discussion =
topic. I am generally considered a reliable source of info but I =
have to admit that my experience on hf is limited. Well to the =
question and I would like all to consider this one.<br><br>I will only =
have the time and money to build one hf amplifier and would like =
constructive inputs for the initial thoughts I have.<br><br>Power supply =
I can happily tackle but the rf deck is the trickiest.<br><br>I have the =
following parts already. <br><br> Tube - Mullard / Philips QY5-3000A =
(tetrode - don't get confused by the 5 in the part number) plate =
dissipation 3000W. Fmax =3D 220 MHz and rated for SSB operation. =
(Was used for tv ultra-linear duty on band 3 170 - 220 =
MHz in the UK). Vmax =3D 5kV and g2max =3D 1kV. Mullard data =
gives an output of 1,5kW at 30 MHz ssb duty with IMD typically 33 to 42 =
dB. Plus, I have the base and g2 decoupling gear from an old tv =
broadcast transmitter. Other tube specs I can post if =
needed.<br><br>Tank inductor - big (about 4" dia and 12" long) =
probably suitable for the low bands. Others I can wind from =
1/4" copper tube which I have on hand.<br><br>Various variable =
capacitors - none really suitable for the anode tuning but probably OK =
for load capacitor duty. Best one about 250pF with approx. 6kV =
rating - tested at 8kV dc.<br><br>Several high power vacuum relays - =
about 10kV is the highest rating.<br><br>Lots of high voltage / current =
rf fixed capacitors.<br><br>Suitable blower - blows the QSL cards off =
the wall at 10 feet and frightens the dog!<br><br>Now - why =
can't I build the tank circuit using the vacuum relays to switch in =
fixed capacitors for each band. I have enough relays for this if =
one uses 160m, 80m, 40m, 20m, 15m and 10m. (My transceiver doesn't =
have the new WARC bands so I don't need to include them initially). =
Using a relatively small vacuum variable for the anode tuning and =
eliminating the normal tank circuit band-switch seems to me to be the =
way to go, in view of the problems some amplifiers suffer =
from.<br><br>Overall physical size doesn't really matter. (The =
power supply will be a separate item for versatility). I can have =
the required metal-work fabricated locally by a craftsman I know. =
(Rather have enough room to make the thing work efficiently than =
try and jam it all into a box which happens to be available). I =
plan to pressurise the anode compartment and use a scheme similar to the =
K2RIW design for 432 MHz with a chimney for the exhaust.<br><br>Basic =
spec. At least 1kW out on ssb or cw - with no strain. =
<br><br>Yes - We should shortly get a 1kW licence class here. =
(I have just finished writing the new regulations for the R.A. and =
part of the regs covers IMD and not running an amplifier at it's limit =
and removing the silly existing regulation which makes it an offence to =
own an amplifier capable of more than 400W! - so big amplifiers =
will become the order of the day).<br><br>Finally - If possible, the =
amplifier should also operate on 6m with similar output.<br><br>Anyway, =
is there a flaw I haven't spotted. Come on guys what have I =
missed. All ideas =
considered.<br><br>John	ZS5JF<br><br><br><br><br> </p>
</font></body></html>
------=_NextPart_000_01BDFEA7.5ACB2C20--
--
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
|