On Dienstag, 31. August 2004 15:50 Patrick Turner wrote:



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.


....but by now I only get about 6W out of a pair of 6V6 while it should be
about 14W. Seems there is still something wrong.

Claus

--
Claus Misfeldt
www.frozenfrog.de