Hifihvn raises an important point about tube amps. They should indeed never be operated without a speaker load, or a reasonably equivalent high power resistor as a load. I too have my doubts that 150 ohms is low enough to be suitable in all cases. And a substantially lower value would, with most amps, mean that the power rating of the resistor would have to increase significantly.
The reason a load is needed is that with no load, abrupt changes in the amount of current that is fed into the primary of the output transformer can produce extremely large voltage spikes, due to a phenomenon called "inductive kickback." The result can be a ruined transformer or output tubes.
The concern is most significant if music is playing through the amp. However, I would not rule out the possibility that even with no signal present, turn-on or turn-off transients might cause a similar effect, perhaps cumulatively over time if not immediately.
Regards,
-- Al
The reason a load is needed is that with no load, abrupt changes in the amount of current that is fed into the primary of the output transformer can produce extremely large voltage spikes, due to a phenomenon called "inductive kickback." The result can be a ruined transformer or output tubes.
The concern is most significant if music is playing through the amp. However, I would not rule out the possibility that even with no signal present, turn-on or turn-off transients might cause a similar effect, perhaps cumulatively over time if not immediately.
Regards,
-- Al