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Part 2: Cathode control & meters

OLD Revisions. New revision HERE

Revision 0 in 2005

Revision 3: november 2010

Revision 3b2: february 2011 (PCB minor change)

Revision 4, december 2013.

No technical changes between rev 3b2 and rev 4 (except 2 side PCB, with solder resist and silkscreen).This "improved" design, use a power MOSFET instead of bipolar darlington transistor TIP147 or equivalent. The reason is to reduce a bit the huge dissipated power in the bipolar, which result is Q1 breakdown, in a lot of cases all around the world. Even at high cathode current (up-to 3 Amps) no need for "mamouth" heatsink plus blower for Q1 MOSFET.

On high voltage detection, a transistor MOSFET, is added to be compatible with the new logic board. A trip system is implemented, in case of excessive grid current. This relay contact is to be inserted in logic card safety chain. An optional HV meter is added on the board.

This card, associated with the logic card, performs the main functions required by a power triode grounded grid amplifier (except amplification).

This design can be used with any other power triode, not only with GS-35b’s.

All necessary meters are included: grid and plate currents, high voltage. Adapt shunts, resistors and voltages to your needs. All values are given as practical examples. All critical components are available at RADIOSPARES or FARNELL.

Schematic diagram

Voltages ranges simulation

Trip system simulation

PCB layout

Circuit board

Cathode RF input circuit design

Some pictures of the cards

Pictures of the cards in a 1 x GS35b amp at 144 MHz

Pictures of the cards in a 2 x GS35b amp at 144 MHz


Internal link to OLD logic board

Internal link to slow rise regulated heater power supply


Simulation of comparisons between bipolar and mosfet

Simulations of trip system

Cathode input circuit design (excel sheet) Calcul_ENTREE_Ampli_Grille_a_la_masse

CATH&METERS_FET.ZIP OLD REVISION with bill of materials, datasheets, and EXCEL calculation sheets.

That’s All Folks !!!!!!

Dominique - f1frv@sfr.fr OR

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