[Heathkit] Question on SB401

[OTAKEBI@aol.com]

Have an SB401 that did a strange one tonight.
I was talking on SSB 10 meters and all at once the ALC meter went from mid 
scale all the way to the right of the meter.
I heard a noise in final cage like a hum.
Switched meter to plate and pressed mike and plate meter pegged all the way 
to the right.
Switched meter to HV and pressed mike and HV dropped from 400 to 300 without 
speaking into mike.
Opened top cover of radio pressed mike. Hum was coming from one of the final 
tubes.
Soon as I keyed the mike it began to hum and started to get red.
The other final looked fine.
Turned SB401 off for about 10 minutes and turned it back on.
All was fine for about 2 minutes then same problems.
All of a sudden all the problems stopped and rig went back to normal.
Spoke to the guys on the net for about 15 minutes and all normal.
Could a tube go bad then good again?
Now that all is normal where do I look for problem?
It looks like if this goes it could take a lot with it.
I have spare tubes and could put one in place of the tube that was humming 
and glowing red but I am getting full output now so should the tube still be 
suspect?
Any help would be great.
Oh, I did replace the finals on the rig about 4 months ago and did it the 
Heathkit way as per book.
I have had no trouble prior to tonight.
Thanks,
Dan N4VET


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