Hello...
Well, after following all the good advice
from you all, I gave 'er a shot and tried firing
it up.
Fireworks inside rectifyer tube. Yellow_Light_Colorz_PDT_21
Here's what happened and the procedure I used:
No variac (saving scarce funds in case I need new PA060)
so I built a dim bulb tester.
Put in a 3a FAST blow fuse (at the suggestion of our gracious host)
Started with no tubes and a 15w bulb, no prob,
shut off.....
Next, 40w bulb waiting several seconds between each..
Then 60w --> 100w.
So far so good..
Next, 7199s, followed same steps... still ok.
Then, added EL34s.... still good.
Next, 5AR4...
(always following the same steps)
15w bulb ok... for approx 1min.
40w bulb.... ok for maybe 2mins... then...
a soft pop and fireworks inside 5AR4.
Next, popped in 2nd 5AR4..
Forgot to put 15w bulb back in, so started with
40w.. (OOOPSie) Yellow_Light_Colorz_PDT_09
After about 2 mins, soft pop and fireworks.
(might have been 1 min.. I forget)
Backround info:
First 5AR4 is "International" branded, but
has "Made in Great Britan" etched in.
Always guessed its a 70s vintage Mullard, and
the shape looks like one, but...
if anyone says otherwise, I'll take your word for it.
2nd 5AR4 is older (ca. 1990 or so) Sovtek.
Neither had a lot of hrs on em, but they WERE
in 2 very old 70s with intermittent (the usual)
problems..
Amp is a total rebuild, except for irons and chassis...
PC3a replica (Vintage Electron) board,
Can cap is the 40-> 80-> 30-> 20 that others
here have used.
Btw... I had the inputs shorted the whole time
and spkrs connected to the OPTs.
Fuse did NOT blow either time!
The Last 5AR4 I have would be next, but I don't
want to risk it till I've heard from you guyz..
Till I have some sense of what might be causing
it, and having made every reasonable attempt
at fixing anything that might be wrong first.
HELP!! :-)
Sooooo frustrating to have come this far only
to get thwarted at the last step..
Thanx much in advance!!!
Greg