DG7YBN / my 432 MHz PA with GS35b Last Update Feb. 10th 2014

432 MHz Cavity PA with Triode GS35b

The amplifier is build as split compartments, HV source and RF deck - which is 19" 4HE.
I bought it 2014.02.09 from DF0MU as they sell a number of their tube backup amplifiers.

It has a circulator (Narda?) in the input and a directional coupler in the output port,
two panel meters: one for bias/anode current, the other to read output and reflected power.
the HV is supplied via an RG-141 PTFE coax with a professional safety plug.

Due to the relatively low anode voltage of 2.8 kV gain is about 11.5 dB (only). Maybe a little more when
running "QRP" power, like from 25 watts of drive to at least 450 watts+ out, see testing data in table below.

Inside the PA compartment: a beautiful cavity (designed by DJ6JJ, make: DJ3FI), all silver plated brass and PTFE,
note the brown plastic stub on left - which is used for fine tuning the input cavity. The outputs plug socket is 7/16.

A few minutes of polishing with a soft piece of cloth brings back the glory of the high times of pre LDMOS age cavity amps

Some data for higher anode voltage that show the ability of that cavity design


        Data N2DX/DJ3FI     My Test

Va          3200 V          2800 V
Ia           850 mA          490 mA
Ia idle       75 mA           95 mA
Vg bias       34 V             -
Ig           170 mA            -
Pin          100 W            25 W
Pout        1500 W           580 W
- - - - - - - - - - - - - - - - - - -
Gain        11.8 dB         13.7 dB
 
Source http://www.nd2x.net/DJ3FI-70-1.html

a ... TURBINE ... or what? Air outlet on right side

This HV Sources weight is 40 kg or 88 lbs

On startup HV is brought up in two steps, 1100 V and to 2800 V after 60 secs
Capactor 32 uF (by SEL) / 3.75 kV, Pabst Blower, solid state relais for soft start.

73, Hartmut, DG7YBN