SSE Post-mortem help

[spopepro]

So my SSE has been working alright for about a week. I've probably been fiddling with it more than I should have... but this morning it died. I'm trying to figure out what happened so that I can fix it.

Music was playing in this exact configuration for 4 hours last night: 480v B+, 380R cathode resistor, Tung-sol (new sensor) 6550s, triode, no feedback. I turned it on this morning and it worked for 1 min before it quickly went silent, one channel slightly before the other. Now one tube has significant getter loss/whitening. Fuse was found to have blown (1.5A slow). Replaced fuse and Power Tx is ok, accurate voltage, no shorts. Cathode bypass caps seem puffy on top--probably need replacing. Cathode resistors give correct readings. No other problems visible.

So I first figured it was my fault for using 50v caps with a higher than normal B+ and adjustable cathode resistors. However, upon further calculation there should have been only about 30v across them. It makes me think something else happened.

What else can I check? I'm going to replace the puffy caps, but I don't feel like I know what went wrong, so I'm afraid to fire it up again.

[rknize]

Tube failure. The white tube has gone gassy and the tube is passing large plate currents. This is causing the voltage across the cathode resistor to go way up, overloading the cap. I had a similar experience in my SSE with those same Tung-Sol 6550s. It didn't go gassy, but it has some alignment issue that makes it red plate for no reason and overload my cathode resistor.

If the tubes are new, get them replaced.

[spopepro]

That's nice to know. Is there any way to verify? I don't want to stick the tube seller with the bill if my amp caused the problem. Thanks!

[rknize]

If the getter is white, the tube is defective.