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Construction photo's of the dual 572B HF Linear Amplifier

I have started building a HF linear amplifier. It will use two 572B valves in grounded grid configuration. I will be posting photo's here during construction. I am busy with college work at the moment, so am doing a little bit of building when I can. Should be an interesting page when the amplifier is finally complete!

4th November 2010

The very first piece of construction; fitting an anode voltage meter to the front panel.

Using a vintage cutting tool to cut the hole for the vintage panel meter. Yes, it was hard work!

kV Panel Meter
Panel meter rear - mounted

kV Panel Meter
Panel meter front - mounted

7th November 2010

kV Panel Meter
Fitted a 5mm aluminium sheet in the bottom of the case for strength and installed the 800VA 1.6kV Torroidal Transformer. Weight: 8Kg (hence the thick aluminium!)

4th December 2010
The horrible task of cutting large holes for meters and squares for rocker switches! Fitted two power switches, a grid current meter and a plate current meter to the front panel.

soft start
Cutting out for the soft start and power switch.

Panel meter cutouts
Cutouts for plate & grid current meters, plate voltage meter, standby/operate switch, soft start switch and main power switch.

Grid & Plate current meters, Plate voltage meter & switches
Meters and switches mounted. Rear view.

Grid & Plate current meters, Plate voltage meter & switches front panel
The front panel so far.

5th December 2010
Built the power supply board.

High Voltage PSU
Made the power supply board out of eight 450v 470µF capacitors with 100kΩ 2w resistors over them for 59µF at up to 3.6kV. As i'm using 2.2kV these should be very happy with 275v on each. 100kΩ resistors will dissipate 0.75W so they too will be happy. Bridge rectifier is made up of twelve 1N5408 rectifier diodes with 1kV 0.1µF capacitors and 680KΩ resistors over each (not added yet).

LC meter
LC meter confirms 59µF (470 ÷ 8 = 58.75).

6th December 2010
Plate choke

Anode Plate Choke
Wound a plate choke on a 22mm piece of overflow pipe 180mm long using 24SWG wire. From the top down, the sections are 20T, 20T, 10T, 10T, 30T, 100T for a total of 190 turns. Inductance is 0.118mH (118µH). It appears to have no resonant spots on the bands I'm building the amp for. Tested with dip meter.

12th December 2010
More panelwork!

Amplifier Layout
Cut out the holes in the back panel for the fan, 2x SO-239 sockets, 2x phono sockets and power socket. Used the same tool as I used with the voltage meter.

13th December 2010
Installed some parts!

Amplifier Layout
Got a fair bit done today. Installed the valve sockets, filament chokes, PSU filter board, plate & load capacitors and plate choke. Also made the parasitic suppressor seen on top of the plate choke. The heater filaments are now wired to the transformer, thats one bit complete!

22nd December 2010
Mounted the chassis in the case

Amplifier Case

Amplifier Case
Installed the soft start resistor, fan regulator, did some wiring, mounted the main chassis plate into the case and installed the front and back panels. Its actually beginning to look like an amplifier!

23rd December 2010
Switched on the power supply!


To be continued...