09-05-2014, 08:09 PM
Fixed. Thanks to your reply. After reading your reply that suggested removing the OT center tap and also unhooking the Plate and screen supplies from the PT, I got cold feet on removing the center tap as the screen supplies would still be hooked up. So I decided to remove the output tubes. At the same time, I started to question my variac so I checked it out as well. I put an 8 amp slow blow in the variac. Turned everything back on (no output tubes) and voltages were ok, no fuses blow. Replaced the tubes one pair at a time. On the last pair, one tube flashed and the 10 amp fuse in the amp blew. The 8 amp slow blow held. Replaced the bad tube and the amp is solid again.
Cause: I have a small stash 60's vintage Tungsol 6550s. I tested them before putting in the amp. I guess one decided to give up after 5 minutes.
Questions: Is there a law of which fuse blows when two or more identical values are in series. The first one in the variac always blew first. Both 10 amp.
If you only remove the plate voltage, does that cause excessive screen current?
Comment: I forgot how much heat SVT's generate. Warmed my shop by several degrees.
Hangman, thanks for the reply. It got me on the right track.
Cause: I have a small stash 60's vintage Tungsol 6550s. I tested them before putting in the amp. I guess one decided to give up after 5 minutes.
Questions: Is there a law of which fuse blows when two or more identical values are in series. The first one in the variac always blew first. Both 10 amp.
If you only remove the plate voltage, does that cause excessive screen current?
Comment: I forgot how much heat SVT's generate. Warmed my shop by several degrees.
Hangman, thanks for the reply. It got me on the right track.