[Charles Xavier]

I have these 2 tubes and they both should glow like pic 2 on both sides. My other pair glow on both sides The sound seems to be the same from both channels. Is the tube in picture 1 going bad ? or is it ok ?

[FullRangeMan]

The first image show one Cathode is off/cold.
If both cathodes should be on the tube is bad.

If the amp electric supplies are arriving OK at the tube pins, the small filament(cathode heater) is disconected inside the tube or other anomalie in regards to cathode or filament.

You can pull out the tube from the socket and get a magnifying glass to see the pins/leads situation inside the tube.

[JakeJ]

I agree with Fullrangeman, you have a bad or open heater on one of the two.

You could use a volt meter set for continuity and test across the 1 & 2 pins, then the 6 & 7 pins.  I believe you will find one of them will read open.  Here is a pin out diagram.



Image credit from the following website: http://www.jogis-roehrenbude.de/Russian/6C33C/6C33C-B-6S33S-VExtendedDatasheetMB.pdf

[Charles Xavier]

Thanks guys, I have a replacement on the way.