Bob,
The tube temps can be measured reasonably well with an IR thermometer. Hot
spots too look for are on the center of the ceramic body and the junction
with the anode. The datasheet lists max temps on both (If I remember
correctly, it's about 200C/150C for the two).
You are right - a big cooler swap out can make a huge difference. For SSB
or fast CW, it's not a huge concern. But for RTTY, the cooling method
including the anode spreaders is job #1.
There is a picture of my amp in operation photographed with a thermal IR
imager (a very very cool toy) on my QRZ.COM page. Love that gadget - wish I
had one for my own!
73/jeff/ac0c
--------------------------------------------------
From: "Robert Briggs" <vk3zl@bigpond.com>
Sent: Wednesday, March 03, 2010 2:37 AM
To: <amps@contesting.com>
Subject: [Amps] Re GI-7B Triodes..
> Hi all, just a few notes regarding the GI-7B, BT and GI-6B triodes....I
> am currently running a pair of GI7BT tubes in a homebrew 80-10 meter
> amplifier....These tubes are little gems particularly if you take the
> trouble to set them up correctly and pay attention to cooling..I am
> running 2500vdc under load at 800ma carrier for around 1150 watts
> output....I have my grid trip set at 180ma but to date it hasn't had to
> activate....
>
> In regards to cooling....I note many of the conversions use a common
> muffin fan blowing air over the standard GI-7B coolers....I am very
> sceptical that this is a very effective way of cooling these tubes and
> would guess that they would be running near their heat limit...I chose
> to install a compact squirrell cage blower into the amplifier when I was
> constructing it...It is rated at 60cfm Jap built, picked up at a
> swapfest....
>
> I took the original coolers off the GI-7BT tubes and replaced them with
> coolers from GI-46B tubes...The GI-46B coolers are an excellent
> substitute and far superior to the standard cast alloy
> coolers....Finding spare 46B coolers may be a bit difficult...I was
> lucky enough to have a friend in Europe who sourced some for me....
>
> I hope this information is of use.....
>
> 73 de Bob..VK3ZL..
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