Kat 6550 - one odd voltage

[Really Aardvark]

I'm new to the electronics game but have completed the build with only one exploding capacitor - those electrolytics don't run well backwards.

All seems well sonically but electrically speaking one voltage is low - g2p (pin 3) on one ECF80 runs at 79v not 95v as specified. Its definitely the valve - swapping the valves over takes the low voltage to the other channel.

The I have questions are
- is this a duff valve?
- does it need to be replaced?
- what effect is it having on the rest of the amp electrically and sonically?

I'm reading Morgan Jones but haven't quite got to grips with it all yet!

Any help, guidance and views would be appreciated.

Thanks in advance

GregS