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Hi Scott--
You have had other replies, but here is an idea to incorporate when you =
are reworking that amp.
A slick thing you can do if the amp isn't already that way:
Paint the inside of the final compartment with black liquid shoe polish =
(the kind that comes in a bottle with an applicator on a wire). (Per =
Rich's suggestions for the SB-220). That causes the metal to absorb the =
radiant energy from the plates instead of reflecting it back at the =
tubes. I couldn't find the liquid shoe polish, so bought 'Stove Black' =
and a 59 cent brush at a hardware store and painted my SB-220 up all =
nice. Heck, I even painted the surface closest to the bleeder =
resistors. I've got the blackest insides of an SB-220 in existence!
Luck to you!
73 de Mike N4NT@wireco.net=20
----- Original Message -----=20
From: Scott Bullock=20
To: amps@contesting.com=20
Sent: Monday, June 28, 1999 9:59 AM
Subject: [AMPS] new to me al-811h amp
I just picked up a used Ameritron AL-811H amp yesterday for real short =
money, it was advertised as broken. It arced everytime you turned it on. =
I pulled it all apart and found a burnt grid resistor on one of the tube =
sockets. Upon further inspection of the tubes, it was noted that the =
plates weren't straight anymore, and the tops and bottoms of them curled =
in towards the grid. The tube that had the blown grid resistor had a =
obvious plate to grid short.=20
These tubes have white ceramic bottoms with no external markings on =
them except for a "P" on the glass. There is some handwritten marking on =
the inside of the tube, but just numbers. Do these sound like the =
Svetlana 811a or some Chinese clone?
Without having the extended experience with 811a tubes as many of you =
do (it's only my 3rd amp), what would cause the plates to curl like =
this-just excessive heat, improper loading, improper cooling?=20
One of the things that I looked at on the 811h amp when I saw this was =
that it only has one area for air outflow, and it looks to favor the =
capacitors in the power supply. The tubes really don't see all that much =
air around them. On my sb200 (2) I had always put a muffin fan on top of =
the amp to pull the hot air out and keep the internal temperature down =
in contests. What's the general consensus on installing a screened vent =
over the rf section to vent air there?
Thanks,
Scott
KA1CLX
Advantage Communications
Professional Wireless Communications
www.radiosonline.com
800-851-RADIO
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<META content=3D"text/html; charset=3Diso-8859-1" =
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<DIV>Hi Scott--</DIV>
<DIV> </DIV>
<DIV>You have had other replies, but here is an idea to incorporate =
when=20
you are reworking that amp.</DIV>
<DIV> </DIV>
<DIV>A slick thing you can do if the amp isn't already that way:</DIV>
<DIV> </DIV>
<DIV>Paint the inside of the final compartment with black liquid shoe =
polish=20
(the kind that comes in a bottle with an applicator on a wire). =
(Per=20
Rich's suggestions for the SB-220). That causes the metal to =
absorb the=20
radiant energy from the plates instead of reflecting it back at the =
tubes. =20
I couldn't find the liquid shoe polish, so bought 'Stove Black' and a 59 =
cent=20
brush at a hardware store and painted my SB-220 up all nice. Heck, =
I even=20
painted the surface closest to the bleeder resistors. I've got the =
blackest insides of an SB-220 in existence!</DIV>
<DIV> </DIV>
<DIV>Luck to you!</DIV>
<DIV> </DIV>
<DIV>73 de Mike <A href=3D"mailto:N4NT@wireco.net";>N4NT@wireco.net</A> =
</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:sales@radiosonline.com"; =
title=3Dsales@radiosonline.com>Scott=20
Bullock</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> Monday, June 28, 1999 =
9:59 AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [AMPS] new to me =
al-811h=20
amp</DIV>
<DIV><BR></DIV>I just picked up a used Ameritron AL-811H amp yesterday =
for=20
real short money, it was advertised as broken. It arced everytime you =
turned=20
it on. I pulled it all apart and found a burnt grid resistor on one of =
the=20
tube sockets. Upon further inspection of the tubes, it was noted that =
the=20
plates weren't straight anymore, and the tops and bottoms of them =
curled in=20
towards the grid. The tube that had the blown grid resistor had a =
obvious=20
plate to grid short. <BR><BR>These tubes have white ceramic bottoms =
with no=20
external markings on them except for a "P" on the glass. There is some =
handwritten marking on the inside of the tube, but just numbers. Do =
these=20
sound like the Svetlana 811a or some Chinese clone?<BR><BR>Without =
having the=20
extended experience with 811a tubes as many of you do (it's only my =
3rd amp),=20
what would cause the plates to curl like this-just excessive heat, =
improper=20
loading, improper cooling? <BR><BR>One of the things that I looked at =
on the=20
811h amp when I saw this was that it only has one area for air =
outflow, and it=20
looks to favor the capacitors in the power supply. The tubes really =
don't see=20
all that much air around them. On my sb200 (2) I had always put a =
muffin fan=20
on top of the amp to pull the hot air out and keep the internal =
temperature=20
down in contests. What's the general consensus on installing a =
screened vent=20
over the rf section to vent air=20
there?<BR><BR>Thanks,<BR>Scott<BR>KA1CLX<BR><B><?bigger><BR>Advantage=20
Communications<BR><?/bigger></B>Professional Wireless=20
=
Communications<BR>www.radiosonline.com<BR>800-851-RADIO<BR></BLOCKQUOTE><=
/BODY></HTML>
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