Power Supply:

The Power Supply is constructed around a 5 KVA Pole Pig Transformer capable of providing several amps in Amateur Service. The 5 KVA Pole Pig Transformer has multiple Primary and Secondary Taps. The 120 VAC Primaries are connected in Series. The Secondaries are in Parallel (full wave bridge rectification) and about 30uF of Filter Capacity (no choke input).

The Power Supply is capable of producing 3900 VDC output plate voltage. Bias is created by a bias circuit board and is adjustable from 17-35 VDC producing an idle current of 40 ma for SSB operation at 3000 VDC. Cutoff of the amplifier in standby is accomplished by using a 560K resistor switched in and out by a relay connected to the transceiver's PTT Line.

The RF Unit/Metering Circuity is mounted on the Bias Board using 1 ohm 1% resistors as reference resistors.

RF Unit - Metering:

The RF Unit has a front panel with 4 Meters; Plate, Grid, Heater and HV. The Power Supply contains 1-130 VAC Variac for adjusting the Heater Voltage (~12.6 VAC at 3 amperes) and twin 120 Variac to control the High Voltage Transformer.

A Time Delay Relay provides a time delay of 3 minutes for heater warm up (sorry, no fast-on with this tube!).

RF Unit:

The RF Unit is constructed around a Roller Inductor. The Inductor is about 15 Micro Henrys. 160 Meter operation is with an additional fixed coil of 12.1 uh. A switch is used to switch in the 160 Meter coil along with a padder capacitor for C1 (Plate Tuning) and C2 (Loading).

The amplifier shows the 300 pf 10 KV Vacuum Variable for PI Network tuning and an Air Variable 1400 pf Capacitor for loading.

I am using a FT2000D which has an internal automatic tuner which I do not use because the amplifier has an input Pi Network for tuning the input.

I have a simple circuit for adding the 160 Meters coil and capacitors to the Pi Network. When this switch is switched in for 160 Meters operation it connects the coil and capacitors to the circuit, when switched out the 160 Meters inductor and capacitors are out of the circuit.

Output Pi Network:

Since a Roller Inductor is used, the Tank Circuit is a PI Network instead of a PI L Network. According to the ARRL Handbook the plate resistance of a class B amplifier is found by dividing the plate voltage under load by 1.8 times the maximum plate current which provides the desired output power. Actually this figure may be as low as 1.57 but it is best to design the PI Network using the higher value of 1.8 because this yields the largest values for the plate and load capacitances, making sure you have enough maximum capacitance! A plate voltage of 3600 V and a plate current of 1 A gives a plate resistance of 2000 Ohms. Lower maximum plate currents, the plate resistance becomes higher and the maximum values of the tuning and loading capacitance decrease. The values for a Pi Network using a plate resistance of 2000 Ohms and a Q of 12 are, according to the ARRL handbook:

R1	Band	C1	C2	L
2000	160	446	2284	17.6
	80	226	1158	8.9
	40	118	606	4.7
	30	84	429	3.3
	20	60	306	2.36

where capacitances are in pf, inductance in uH.

Using these values the 300 pF and a fixed padder the tuning capacitor I have will comfortably reach the maximum value of tuning capacitance required. The 1400 pf Air Variable with a fixed 1500 pF loading capacitor will require a switch for the fixed capacitance in parallel. This will be easily accomplished using an addition switch contact on the switch used.

If a higher plate voltage and lower plate current are used the plate resistance can be much higher. If the plate voltage was 4000 VDC with a maximum plate current of 0.8 Amps the plate resistance works out to 2778 Ohms. I used a computer program and calculated the Pi Network values for this plate resistance and a Q of 12, since the ARRL handbook doesn't provide them. The computer program used gave close values to the ones in the ARRL handbook for lower plate resistances. The table for 2778 Ohms is:

R1	Band	C1	C2	L
2778	160	348	1908	24.5
	80	179	982	12.6
	40	89	491	6.3
	30	62	340	4.37
	20	45	245	3.15

These values are even easier to obtain.

Parasitic Choke:

The Parasitic Choke Resistor is made from a carbon rod taken from a D Cell Battery. The carbon rod is 2 1/2 inches in length, diameter is 5/16 of a inch, and has a resistance about .7 Ohms. The coil is 12 Ga. Copper Wire with three turns. Connections are made to the carbon rod with copper pipe straps.

Plate Choke:

The Plate Choke is a 1" diameter Ceramic Form with a six inch length of 1/2 inch diameter Ferrite Rod installed in a hole inside the choke to raise the inductance. Using this method, will increase inductance, reducing the need for a large single layer choke, which can be wound with less turns, removing any self resonances from the ham bands.




Tuned Input Values for GS-35B:

Band - C1 Input / L / C2 Output (cathode)

160 - 2400pf / 3-5uh       / 2000pf
 80 - 1330pf / 1.8-3.3uh   / 1165pf
 40 -  700pf / 0.6-1.8uh   / 600pf 
 20 -  390pf / 0.2-.6uh    / 320pf 
 15 -  200pf / 0.08-.2uh   / 130pf 
 10 -  100pf / 0.02-0.08uh / 180pf

Operation:

Before you can use this tube it needs to be "Regenerated". The internal plate structure has a coating (gitter) which absorbs any gasses present, at high temperature, so the tube has to be "cooked" and burned in. This is accomplished by slowly increasing the heater voltage over 10-12 hours to full voltage with out high voltage present.
Next
The tube can be cooked by, bypassing biasing voltages, and running the tube at 1800 VDC. The idle current at 1800 VDC should be around 250 ma with zero bias. The tube needs to be run under these conditions for 4 or 5 hours, with full forced air cooling--to remove the heat. After finished with the last step, the amplifier should be put into a Dummy Load at about the same plate voltage (1800 VDC) and current for several hours, then it can be operated FULL BORE!

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