Major steps on the Gu74B 1 Kilowatt amplifier

Some major steps has been taken since the last post. The structural part of the chassis assembly is finished. (When you build an amplifier; actually half of the work is in the workshop). What is missing now are the holes in the front panel for switches, shafts and metering.

I will also start posting parts of the circuit diagram below.

Overview picture of the amplifier:

I have started with parts of the Mains wiring, mounted the blower and the socket in the pressurized sub chassis. The air intake is in the upper right corner, just to left of the Power Entry Module. The blower the then drags air through the PS compartment, and then through a hole in the wall between PS and the RF deck. The air exhausts through the tube cooling fins and up through a chimney and finally through a hole in the top cover.

Detail pictures:

The blower is obtained from the very helpful people of Airflow UK; http://www.airflow.co.uk/. It is rated 31 CFM at 0.5 inch back pressure, which is 50% above the tube specification. I hope this will be enough considering that the airflow will be somewhat hindered by all the components in the PS compartment and in the RF deck.

All wiring follows European standard; blue for Neutral and brown for Live!

Parts of the Mains wiring. All connections are shrink tubed to prevent accidental contact!

Safety interlock switch. If the top cover is removed. HV is instantly disconnected. But of course; you should never take of the top cover on a live High Voltage Power Supply! Still you also have to think of the capacitor bank which can take up to a minute to fully discharge. But more on that when we come into the filtering section!

Heavy Duty relays in the Mains circuit to cope with high current surges!

Circuit diagram of the Mains wiring:

Here is the first part of the schematics. I will add more as we get further into the project. Here is how it works:

When the Mains switch in the Power Entry Module (The Power Entry Module contains switch, fuses and EMI filter) is turned on power will be present in the control transformer, blower and mains indicator on the front panel. In this stage the amplifier rests until the HV ON switch on the front panel is activated. When HV ON is switched, 12 volts DC will be present on the first relay. When the relay is actuated 230 volts will be present on the HV transformer primary. But the current will actually start flowing in two steps. For the first half second the current will be limited by the resistor in series with the Live lead to the transformer. When the capacitor is charged, after about 0.5 seconds, the second relay will actuate and bypass the resistor. The purpose of this step start is to take stress off from the large capacitor bank in the DC circuit of the Power Supply.

At this stage; grid voltages will be applied before the cathode is heated. I will have to adress that later with some kind of delay circuit.

The circuit diagram is done by the help of TinyCAD. An Sopen Source software available at: http://tinycad.sourceforge.net/