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I really doubt that the excellent Gi7b(t) tube will do what Tom is =
stating, I know the tube well and I'm using it in a 144MHz amp. It is, =
as Tom states, a very robust and abuse tolerant tube, but this is really =
pushing it beyond whats credible.
Specs say 350W, Ft over 1GHz, and 2.5KV in class C. It is a Russian =
military tube built like a tank, and indeed designed for use in tank =
radars. The tube will take a lot af abuse without apparent short term =
ill effect.
I run a single tube at 2.1KV and 400mA class AB giving out some 425W on =
144MHz when running SSB or CW, and 300W+ when running WSJT (100% output =
, 30s on 30s off), using just an 18w muffin fan for cooling!
Before I got the design stabilized I had a lot of violent flashovers and =
other mishaps, but the tube has withstood all of that plus two incidents =
of near meltdown (as a result of accidentially overdriving (50W instead =
of 10W in WSJT mode)), and is still running at full spec. The tube was =
litterally red hot both times, and took some minutes to cool down again, =
whereupon I could resume normal operation. What happens with my design =
and this tube is a thermal runaway: as the tube gets hotter is becomes =
mistuned, and the output is reduced to almost NIL, while the tube sucks =
up all the mAs that the powersupply will give, dissipating (or rather =
not dissipating) everything as heat.
Vy 73 de OZ1PIF, Peter
********** OZ1PIF **************
email: oz1pif(no-spam-filler)@get2net.dk
http://hjem.get2net.dk/oz1pif
Ph. +45 4619 3239
Snailmail:
Peter Frenning
Ternevej 23
DK-4130 Viby Sj.
Denmark
***********************************
----- Original Message -----=20
From: Tom Hix=20
To: amps@contesting.com=20
Sent: Saturday, February 02, 2002 9:05 AM
Subject: [AMPS] Alpha 76 and 78 tube conversions
Snip....
I believe these tubes would possibly be a good solution for many of =
the people who own the older Alpha amps like the 76 and 78 series, who =
dont want to pay $1200.00 to $1500.00 to retube their amps. These tubes =
are really heavy duty. A pair of them will give you about 1200 to 1400 =
watts depending on voltage and drive. There is an article on my site =
about the conversion a friend of mine did on an older Dentron amp that =
ran 4 572b tubes. He put in a pair of the gi7b tubes and was able to =
make a real nice amp out of it. He gets about 1200 to 1300 watts out on =
the pair of gi7b tubes.=20
Snip snip......
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<DIV><FONT face=3DArial size=3D2>I really doubt that the excellent =
Gi7b(t) tube will=20
do what Tom is stating, I know the tube well and I'm using it in a =
144MHz amp.=20
It is, as Tom states, a very robust and abuse tolerant tube, but this is =
really=20
pushing it beyond whats credible.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Specs say 350W, Ft over 1GHz, and 2.5KV =
in class C.=20
It is a Russian military tube built like a tank, and indeed designed for =
use in=20
tank radars. The tube will take a lot af abuse without apparent short =
term ill=20
effect.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>I run a single tube at 2.1KV and 400mA =
class AB=20
giving out some 425W on 144MHz when running SSB or CW, and 300W+ when =
running=20
WSJT (100% output , 30s on 30s off), using just an 18w muffin fan for=20
cooling!</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Before I got the design stabilized I =
had a lot of=20
violent flashovers and other mishaps, but the tube has withstood all of =
that=20
plus two incidents of near meltdown (as a result of accidentially =
overdriving=20
(50W instead of 10W in WSJT mode)), and is still running at full spec. =
The tube=20
was litterally red hot both times, and took some minutes to cool down =
again,=20
whereupon I could resume normal operation. What happens with my design =
and this=20
tube is a thermal runaway: as the tube gets hotter is becomes mistuned, =
and the=20
output is reduced to almost NIL, while the tube sucks up all the mAs =
that the=20
powersupply will give, dissipating (or rather not dissipating) =
everything as=20
heat.</FONT></DIV>
<DIV> </DIV>
<DIV>Vy 73 de OZ1PIF, Peter</DIV>
<DIV> </DIV>
<DIV>********** OZ1PIF **************<BR>email:=20
oz1pif(no-spam-filler)@get2net.dk<BR><A=20
href=3D"http://hjem.get2net.dk/oz1pif";>http://hjem.get2net.dk/oz1pif</A><=
BR>Ph.=20
+45 4619 3239<BR>Snailmail:<BR>Peter Frenning<BR>Ternevej 23<BR>DK-4130 =
Viby=20
Sj.<BR>Denmark<BR>***********************************</DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:w4th@hotmail.com"; title=3Dw4th@hotmail.com>Tom =
Hix</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
href=3D"mailto:amps@contesting.com"=20
title=3Damps@contesting.com>amps@contesting.com</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, February 02, =
2002 9:05=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [AMPS] Alpha 76 and 78 =
tube=20
conversions</DIV>
<DIV><BR></DIV>
<DIV>
<DIV>
<DIV>
<DIV></DIV>
<DIV></DIV>Snip....
<P>I believe these tubes would possibly be a good solution for many of =
the=20
people who own the older Alpha amps like the 76 and 78 series, who =
dont want=20
to pay $1200.00 to $1500.00 to retube their amps. These tubes are =
really heavy=20
duty. A pair of them will give you about 1200 to 1400 watts depending =
on=20
voltage and drive. There is an article on my site about the conversion =
a=20
friend of mine did on an older Dentron amp that ran 4 572b tubes. He =
put in a=20
pair of the gi7b tubes and was able to make a real nice amp out of it. =
He gets=20
about 1200 to 1300 watts out on the pair of gi7b tubes. </P>
<P>Snip snip......
<HR>
</P></DIV></DIV></DIV></BLOCKQUOTE></BODY></HTML>
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