Tube Current

[Blair]

This has been something I have wondered about for a while, so hopefully I can get a bit of clarification.

Most datasheets have a max signal current that is super high. I get in response from posts "these are extreme circumstances".

So, there is also a min/idle current.

The question is, how much fluctuation in current is there? For example: MKIII. You bias each tube at 55-65mA, so there is an idle current of 110-130mA. The original PT is rated at 200mA, but triode has a replacement rated for 300mA.

Clearly, the overhead is nice, but the original had no issues reaching 60W.

So, is there a idle/max current ratio that is good for estimating what is needed to drive a PP circuit?

I know the average DIYer would simply say, "I just make sure I double the current expected to be needed", but what is the manufacturer rule of thumb.

Thanks,

Blair

[kheper]

So, there is also a min/idle current.


So, is there a idle/max current ratio that is good for estimating what is needed to drive a PP circuit?

I know the average DIYer would simply say, "I just make sure I double the current expected to be needed", but what is the manufacturer rule of thumb.

There is no "manufacturer rule of thumb". It depends on the particular design of the amp. From Genelex:

http://www.triodeel.com/kt88p4.gif

AB1 UL Fixed bias:
Ia+g2(idle) = 2 x 50ma
Ia+g2(max)= 2 x 157ma

http://www.triodeel.com/kt88p3.gif

AB1 UL Cathode bias:
Ia+g2(idle) = 2 x 87ma
Ia+g2(max) = 2 x 99ma