KT88 in class B

[Saint Vith]

Hi, I found in Internet that is possible connect 2 kt88 in class B and get 150 W. Do you know specifications about this connection ?
load impedance, B+, Vg2, Vg1, etc.

Thank you

[DougL]

I looked on the data sheets found by Duncan Amp TDSL.

Listings were Class AB1 Between 50 and 100 Watts in Pentode / Beam Tetrode Mode.

My Guess is for maximum power, you are going to be at or near maximum on both plate voltage, and G2 voltage of 800V and 600V respectively.
The transformer primary impedance should be about double the class A Pentode Z. Guess of 6600 to 8000 Ohms would be optimum.

Bias voltage would need to be determined, but it is very near cutoff on class B. The 625 / 600 V, 100W bias was -45 and Rl (a-a) was 5000 ohms

GEC KT88 Data, Page 2

Hope this helps.

Doug

[Saint Vith]

Thank you DougL, I have a 9kohms primary impedance output transformer. First I will do the most simple. Vplate 800 V, Vscreen 400 V (I will take this V from the mid point of electrolitic caps in serie connection, the H.T. secondary have a mid point that I connect to the mid point of caps). I will tell you the results.

Thank you Juan.

[richwalters]

GEC application report No.3 for KT88 Describes a 150W class B ICAS amp with 88's. (June 1972 issue3). The KT88 is config as triodes.

In brief

B+ = 850V
Vg2rms =60V
Ia= 2x10mA
Ia max sig = 2x140mA
Ig1+g2=30mA
Pout=150W
RL A-A =6Kohms (speech applications) ICAS
Zout =25Kohms
D=6-8%
Pdr approx=7W
Vin (g-g)rms=360V
Zin=18Kohms

For other applications RL A-A be increased to 7.5Kohms.

( with B+ at 600V 100W is given)

Driver stage must be capable of supplying 180+180V rms.

The driver stage is a basic cathode biased using a centre tap feed choke of approx 20H < 500ohms. Small o/p tranny can be used as subs.

I've got an article but it isn't fully complete.

ICAS = Intermit Commercial & Amateur Service.

There must be a full article somewhere on the web.

richj