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k1ta@contesting.com: wrote
>=20
> >GSeven wrote:
>=20
> >> I thought it would tune around at least 25pf bit its back all the way=20
> out.
> >> What should I expect to see with say 100 watts provided the tank is=20
> right?
2000 W output are to be expected
>=20
> >Answer Not much The 3CX-3000A7 is notorius as being a Pig to drive. Th=
e
> >spec sheet states that 410 watts is required to drive it to 2.0 Amps of
> >plate current. With 100 watts don't expect much more than 500 mils of pla=
te
> >current with the tube biased correctly.
>=20
> >As to 10 meters not tuning that is also predictable. The 3000 has an
> >inordinately high output capacitance. 38pf Compare this to the 8877 and
> >4CX-1500A which each have values of 10 pf and its understandable that you
> >are not able to tune 10 meters.
>=20
Should be no problem to tune 10m, just raise the Q of the Pi-Circuit or use=20
Pi-L,
output capacity of the tube is just 24pf by Eimac datasheet.
Tuning Capacitor should be vacuum type for low minimum C.
I run 3 large glass envelope tubes with about 40pf Cout with equal effiency=20
on 10m
as on other bands. ( L=3D 0,4 =B5H ), RL is similar to 3CX3000A7s tuned=20
condition.
> >Finally the plate voltage that you state you are using (6700 volts) is a
> >full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
> >Volts. BE CAREFUL !
I would recommend to use 4 to 4,5 KV to keep RL low, tuning on 10m will be=20
much easier then,
probably a bit more drive will be needed, but no problem to get >1500 out=20
with 100W of drive.
>=20
> >It appears that Eimac intentionally developed this tune with the objectiv=
e
> >of keeping it out of the hands of Hams and CBers. My recomendations, if y=
ou
> >have this Amp running on all bands but 10 declare victory and leave it
> >alone. Drop the Plate Supply to 5000 volts and limit the service of this
> >amp to 14 Mhz and below.
>=20
It appears to me as a funny idea that Eimac did it by purpose....
The relatively high capacity is produced automatically by the larger=20
structure of course !
My amplifier for 144Mc runs very nicely with 12db gain by this triode as=20
well.=20
73
Peter
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<HTML><FONT FACE=3Darial,helvetica><FONT SIZE=3D2> k1ta@contesting.com: wro=
te
<BR>
<BR>
<BR><BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px solid; MARGIN-=
LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">
<BR>>GSeven wrote:
<BR>
<BR>>> I thought it would tune around at least 25pf bit its back all t=
he way=20
<BR>out.
<BR>>> What should I expect to see with say 100 watts provided the tan=
k is=20
<BR>right?</FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=
=3D"Arial" LANG=3D"2"></BLOCKQUOTE>
<BR>
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">2000 W output are to be expected
<BR>
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"><BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px so=
lid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">
<BR>>Answer Not much The 3CX-3000A7 is notorius as bein=
g a Pig to drive. The
<BR>>spec sheet states that 410 watts is required to drive it to 2.0 Amps=
of
<BR>>plate current. With 100 watts don't expect much more than 500 mils o=
f plate
<BR>>current with the tube biased correctly.
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"></BLOCKQUOTE>
<BR>
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"><BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px so=
lid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">>As to 10 me=
ters not tuning that is also predictable. The 3000 has an
<BR>>inordinately high output capacitance. 38pf Compare this to the=
8877 and
<BR>>4CX-1500A which each have values of 10 pf and its understandable tha=
t you
<BR>>are not able to tune 10 meters.
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"></BLOCKQUOTE>
<BR>Should be no problem to tune 10m, just raise the Q of the Pi-Circuit or=20=
use=20
<BR>Pi-L,
<BR>output capacity of the tube is just 24pf by Eimac datasheet.
<BR>Tuning Capacitor should be vacuum type for low minimum C.
<BR>
<BR>I run 3 large glass envelope tubes with about 40pf Cout with equal effie=
ncy=20
<BR>on 10m
<BR>as on other bands. ( </FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"=
SANSSERIF" FACE=3D"Arial" LANG=3D"2">L=3D</FONT><FONT COLOR=3D"#000000" SIZ=
E=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"2"> 0,4 =B5H ), RL i=
s similar to 3CX3000A7s tuned=20
<BR>condition.
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"><BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px so=
lid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">>Finally the=
plate voltage that you state you are using (6700 volts) is a
<BR>>full 33% over the manufacturers Maximum recommended Plate Voltage of=
5000
<BR>>Volts. BE CAREFUL !</FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=
=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"2"></BLOCKQUOTE>
<BR>
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">I would recommend to use 4 to 4,5 KV to keep RL low, tuning=20=
on 10m will be=20
<BR>much easier then,
<BR>probably a bit more drive will be needed, but no problem to get >1500=
out=20
<BR>with 100W of drive.
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"><BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px so=
lid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">
<BR>>It appears that Eimac intentionally developed this tune with the obj=
ective
<BR>>of keeping it out of the hands of Hams and CBers. My recomendations,=
if you
<BR>>have this Amp running on all bands but 10 declare victory and leave=20=
it
<BR>>alone. Drop the Plate Supply to 5000 volts and limit the service of=20=
this
<BR>>amp to 14 Mhz and below.
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"></BLOCKQUOTE>
<BR>It appears to me as a funny idea that Eimac did it by purpose....
<BR>The relatively high capacity is produced automatically by the larger=20
<BR>structure of course !
<BR>
<BR>My amplifier for 144Mc runs very nicely with </FONT><FONT COLOR=3D"#000=
000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=3D"2">12db gain </FON=
T><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Arial" LANG=
=3D"2">by this triode as=20
<BR>well.=20
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D3 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2">
<BR>73
<BR>
<BR>Peter
<BR></FONT><FONT COLOR=3D"#000000" SIZE=3D2 FAMILY=3D"SANSSERIF" FACE=3D"Ar=
ial" LANG=3D"2"></FONT></HTML>
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