Claus Misfeldt wrote:

On Dienstag, 31. August 2004 11:22 Fabio Berutti wrote:

The data You saw are correct: they are only referred to A COUPLE of tubes
as it was common practice for PP pairs.
As per the dissipation:
- first, the tube only sees V difference among cathode and anode:
therefore, if the feed ing voltage is 305V and the cathode bias is 19V,
the tube works actually with (305-19)=286V

...agreed

- second, when fitted with cathode bias the system is already
self-regulating. It seems Your amp has a common cathode resistor for both
tubes. In this case, the current cannot be 26 mA per tube: being the
cathode bias given by V=RxI it follows 19=270xI - I=70.37 mA per pair as
per tube D/S.

-19V Bias is from the data sheet. I measured by two ways:
1.) 267 Ohm (measured) / 14,9V (mesured drop)= 56mA; 56/2=28mA
2.) Resistance of prim. leads of OT: 109 Ohm; Voltage drop on that, when
idle 2,78V = I= 26mA

Would you agree in saying, that this current seems to be a bit too low?

28mA would be about right for Ik
at Ea = 285v.

Patrick Turner.



Regards
Claus

--
Claus Misfeldt
www.frozenfrog.de