30 seconds sounds about right for a tube to heat up and go over current.
1/2A may not be enough fuse, so blowing the fuse may just be a diagnostic
that the fuse is doing its job -- get the right fuse to start with.
With Heathkits, you always need to ask the question "did it ever work?".
Then you need to ask "did it ever work _right_?". Then "was it
modified?". Then, finally, open it up and visually inspect everything
not just for the obvious like burnt components or wires, but for the less-
obvious assembly errors like cold solder joints, wires broken because of
improper assembly, wires put in the wrong places*, etc.
Inspect with your eyes _and_ your nose -- if you get a whiff of "that
expensive smell" then track down what's burnt. When you turn it on (out
of the case, of course), go over it with your nose again -- your nose not
only smells, but it's a pretty good heat sensor, sometimes you can
"smell" warm air coming from a too-hot component before it actually
starts smelling burnt.
If it still blows the same way with a 1A fuse then start checking tubes
for proper bias and shorts and stuff. Then check all of the power supply
voltages to make sure they're correct.
If it's solid state other than the CRT this'll be easy. I would think
that if the CRT is pulling too much current that you'd have seen a honkin'
bright spot, but I suppose that if the biases were really all shot to
hell then you may have just lit up the whole screen and not noticed it --
power it up in a dark room the next time and see.
And tell us what model it is, and other essential things like how many
tubes!
* I'm partially color blind in green and red, so my Heathkit oscilloscope
got assembled with a green wire swapped for a gray wire. One was a 160V
bias, the other was a 5V signal. I made expensive smells with that one.
But then, I fixed it, too.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com