talsmaja wrote:Hi all,
I have a Bob Latino kit st-70 that I built in 2012 that has worked perfectly until just recently when it blew a fuse. I bought some replacement 3A slo-blo fuses and after replacing the fuse and turning the amp on the following happened: The tubes lit up and within seconds of turning the amp on I saw an arc in the rectifier tube and the fuse blew again. Does this sound like I need a new rectifier tube or new output tubes? Thanks!
It is the most probable cause.
But, it might also be a problem with something draining B+, a broken can cap, a el34 that flashes.
If you don't possess an external B+ powersupply to test with you could
rule out the above at the cost of possibly breaking another 5ar4 by this procuedure:
replace 5ar4 with a new one. Remove the el34's on one side ( keep note of
their positions ) power on. The results is one of :
-1 works fine.
-2 fuse blows
If (1) then reinstall the el34's in their original positions and power on again
if everything works you are done, the fault was the 5ar4.
If (2) , reinstall the el34's in their original positions, and remove the other
el34, noting their positions. AT this point the 5ar4 might have been destroyed
but do continue. If amp powers up and works with one channel the fault was in
one of the removed el34. If the fuse blews again you have a problem
with either faulty can cap or the new 5ar4 has been broken . Replace the can
cap and get a new 5ar4.
The above sequence should identify the problem in 90% of all cases. If
not i suggest you find a workshop .