Minimum Heater Current

[gtto]

This is kind of an offshoot of another thread I started. If you are interested that thread is http://music-electronics-forum.com/t42828/ . The amp is a Fender Supersonic 60. Output tubes are two 6L6GC. The transformer was replaced with a Hammond 290VEX. Problem is that it is 240V and I am in a country with 220V. So now what I get is 5.4VAC across P13/P14, 24VAC across 15/16, 24.2VAC across 16/17 and 24VAC at tp10. Plate voltage at pin 5 is 418 V But it has been as high as 430V. If I was in the states I would have already bought the proper transformer but by the time it is shipped and goes through customs it could cost $400. My question.....is the heater current hot enough to not cause cathode poisoning or some other problem? If it will cause poisoning what exactly will that do and how long could it take? Thanks in advance. I am kind of new to this and people on this forum have been a great help.

[nickb]

This is kind of an offshoot of another thread I started. If you are interested that thread is http://music-electronics-forum.com/t42828/ . The amp is a Fender Supersonic 60. Output tubes are two 6L6GC. The transformer was replaced with a Hammond 290VEX. Problem is that it is 240V and I am in a country with 220V. So now what I get is 5.4VAC across P13/P14, 24VAC across 15/16, 24.2VAC across 16/17 and 24VAC at tp10. Plate voltage at pin 5 is 418 V But it has been as high as 430V. If I was in the states I would have already bought the proper transformer but by the time it is shipped and goes through customs it could cost $400. My question.....is the heater current hot enough to not cause cathode poisoning or some other problem? If it will cause poisoning what exactly will that do and how long could it take? Thanks in advance. I am kind of new to this and people on this forum have been a great help.

Honestly, I don't know the answer to your question. I'd be surprised if it were a big problem.

But why live with it? You can buy a small 20VA 220 (220-240 will be fine) to 20V 1A transformer for very little and wire it to step up the input to your Supersonic. If you wire the phase of the boost transformer wrong you'll get 200V instead of 240V.

[g1]

The 5.4VAC is the heater voltage.
The heater current is another problem that was mentioned in the other thread. The 290VEX hammond is rated for 3.8A on the heater winding, the Supersonic 60 runs at about 4.2A from the heater winding.
The question was whether this is significant enough to cause any overheating. As it's only a 10% difference, it should probably be ok, but if not you can use an external transformer just for the heaters.