Antonio Vernucci wrote:
I am planning to build a suppressor-grid modulated AM transmitter.

In all the diagrams I have seen they use proper pentodes, i.e. tubes
that have a real suppressor grid (e.g. 803).

I have seen no diagram using beam power tubes (e.g. 813 or 814) which
have beam forming plates instead of the suppressor grid .

Before purchasing 803 tubes, I would like to be sure that 813s or 814s
are really unsuitable for suppressor-grid modulation.

My question is whether, with 813s or 814s, the plate current can be
actually controlled by varying the beam forming plates voltage.

Does anyone have experience on that issue?

73

Tony I0JX

Rome, Italy

A little late, but could be of interest:

Try the 2E22 valve.

I used to work with this excellent valve during my military service in
1968, repairing military equipment that used it as supresor modulated.

It was built especially for that purpose.

Here are the specifications:

2E22
Power Pentode

Base & Bulb
EIA Base 5J

Mechanical Data

EIA Base ...................................... 5J
Electrical Data

Heater Voltage ................................ 6.3 V
Heater Current ................................ 1.5 A
Direct Interelectrode Capacitances (approx)

Pentode
Input ......................................... 13 pf
Output ........................................ 8 pf
Grid to Plate ................................. 0.2 pf
Maximum Ratings (Design Center Values)

Pentode
Plate Voltage ................................. 750 V
Grid No. 2 Voltage ............................ 250 V
Plate Dissipation ............................. 30 W
Grid No. 2 Dissipation ........................ 10 W
Characteristics and Typical Operation

Class C Oscillator/Amplifier
Plate Voltage ................................. 750 V
Grid No. 3 Voltage ............................ 22.5 V
Grid No. 2 Voltage ............................ 250 V
Grid No. 1 Voltage ............................ -60 V
Grid No. 1 Current ............................ 6 mA
Plate Current ................................. 100 mA
Grid No. 2 Current ............................ 16 mA
Driving Power ................................. 0.55 W
Power Output (approx) ......................... 53 W
Characteristics and Typical Operation

Class C Modulated Amplifier (Supressor)
Plate Voltage ................................. 750 V
Grid No. 3 Voltage ............................ -90 V
Grid No. 2 Voltage ............................ 250 V
Grid No. 1 Voltage ............................ -90 V
Plate Current ................................. 55 mA
Grid No. 2 Current ............................ 29 mA
Power Output (approx) ......................... 16.25 W

Alejandro Lieber
LU1FCR
Rosario - Argentina

Real-Time F2-Layer Critical Frequency Map foF2 at:

http://1fcr.com.ar