Of Sections In Each U

ID w CHANGE-OVER

Fig, 2. Power supply schematic>

Bottom view. Notice the shield which isolates the output section from the rest oj the circuit*

glow of the plates. However, I prefer to use an output indicator such as an SWii bridge or a monitor scope. Adjust the plate tuning capacitor (C5) until the output indicator reads maximum, then adjust the loading capacitor (C6: until the output indicator again reads maximum, Switch in additional capacity (C7, C8, C9) as required and retune (C6).

lie last step is then to readjust (C5) for maximum.

The 4E27s in this circuit amplify about 10 to 1 on 10 meters. So 100 watts driving power could get you 1000 watts to the plates, therefore, be careful not to burn up the tubes. Always tune up with reduced power

Power supply. \o thing critical here at all.

Power Supply

The power supply circuit for this 4E27 amplifier is illustrated in Fig. 2, A 10 x 12 x 3 inch chassis allows you plenty of room for all the power supply components.

The diode strings are mounted on terminals on a perforated epoxv glass board. The terminal mounting tools were a tack hammer and an almost blunt center punch.

The bleeder resistor is composed of ten 20 k resistors in series, Five watt resistors are adequate, but al] 1 had was 50 watt resistors, so that's what I used. However, the larger resistors may be used in the future as a voltage divider for screen and suppressor grid voltages if you decide to change over to type AB^ operation.

Operating the power supply is very simple, all you have is an on-off switch. The

Power supply. \o thing critical here at all.

The bottom of a power supply is the bottom of a power supply.

117 V ac relay makes and breaks the primary side of the power transformer. This eliminates any possibility of hash from the power supply while it's on stand-by.

A 300 mill dc ammeter in the cathode circuit of the power supply gives you an indication of how much B4- current you are drawing.

General Comments

If VOX operation is used, be sure to set the change over relay for a long delay so the unit will not change over on pauses in words. Rapid continuous keying of the power supply relay may cause an excessive load on the power supply.

I would like to thank Don Bristol, W6ZUI, for his assistance in developing this amplifier and for furnishing the major components

Amplifier and powt*r supply such as tubes, transformers, chokes and capacitors, One capacitor, the plate tuning capacitor (Co), was in a Bendix Frequency Standard aboard the Squalus submarine when it went down May 231 1939 off the coast of Portsmouth, N.H, in 240 feet of salt water. Three months later when the submarine was pulled to the surface, much of the electronic gear was reclaimed including capacitor (C5),

Many thanks also to my good neighbor Marty Jacobson for the fine photos.

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