That looks like the blocking cap for the driver tubes, under the chassis deck. If it's bad, it will probably heat up as the power drops. But it's not safe to put your finger on it to find out. Not with 900 Volts on it. A picture with a wider view would tell us what it's connected to. More than one of those caps in this model as a rule.
73
73
...runna pile-up on 6m SSB