4-1000A Kilowatt Amplifier Designed and Built by: Jay Bennett, AA6GK 1989 Edition Page 1 SPECIFICATIONS Frequency Coverage: 160 through 10 meter amateur bands; single knob bandswitched. 1800 - 2000 KHz input power:120w output power: 2100w 3500 - 4000 KHz 120w 2200w 7000 - 7300 KHz 120w 2200w 14000 - 14350 KHz 120w 2000w 18000 - 18200 KHz 120w 1800w 21000 - 21450 KHz 120w 1800w 24800 - 30000 KHz 120w 1650w Modifiable for any frequency between 1.6 and 30 MHz. Power Requirements: Plate Supply 240 vac 60 Hz @ 35 amps 3 prong "dryer" type plug provided optional: 208 vac 60Hz @ 40 amps with 120 vac ct 120 vac 60Hz @ 70 amps R. F. Cage 120 vac +/- 5% 60Hz @ 5 amps Demand Power 'ON', 450 watts Power 'ON', Plate 'ON', 1000 watts Power 'ON', Plate 'ON', amp keyed: 1600 watts Power 'ON', Plate 'ON', full output: 4300-6000 watts Input Characteristics and Drive Requirements: Input circuits pi-network 50 ohm input adjustable L, Q=2 to 3 Input SWR less than 2:1; SO239 connector Drive 80 to 180 watts Output Characteristics: Output circuits pi-network 50 ohms silver plated coils vacuum variable tuning and loading capacitors SO 239 connector Output power 1500 to 3000 watts rms depending on drive 1500 to 4500 watts peak ssb " " " Efficiency 50% to 70% Amplification 11 db. to 13db. Fusing: Plate Power supply ac line 25 amp household screw in. high voltage lead 2 1/2 amp agc R. F. Cage ac line 5 amp mdl slow blow note: Plate Power supply and R. F. Cage are safety interlocked Weight: Plate Power supply 150 lbs. (72 Kg.) R. F. Cage 35 lbs. (17 Kg.) Changeover Relay: Jennings vacuum relay, 24 volt d.c. coil Keying line voltage-30 vdc 300 ma max. Page 2 FRONT PANEL CONTROLS Plate Tuning vacuum variable with turns counter Plate Loading vacuum variable with turns counter Bandswitch Wattmeter selector SWR sensitivity potentiometer Power on rocker switch and panel indicator Plate on rocker switch and panel indicator ALC level potentiometer Keying control rocker switch and panel 'on air' indicator REAR APRON R. F. Cage fuse Octal socket for plate power supply control leads Idle bias control switch Type HN high voltage connector Keying control jack, RCA audio ALC output jack, RCA audio Ground binding post Input SO 239 connector Output SO 239 connector AC power cord- R. F. Cage (polarized) Note: Low pass filter is screwed to back panel TOP OF CHASSIS AND INSIDE Filament voltmeter adjustment Plate current meter adjustment Parasitic suppressor adjustment RIGHT SIDE OF CHASSIS wattmeter scale adjustment pots INPUT CIRCUIT SUBCHASSIS input circuit inductor adjustments WATTMETER SENSOR SUBCHASSIS bridge balance trimmers ****************************************************************** * * * DANGER!! * * * * THE PLATE POWER SUPPLY IN THIS AMPLIFIER IS CAPABLE OF * * * * 6000 VOLTS AT 30 AMPERES INSTANTANEOUSLY. EXERCISE * * * * EXTREME CAUTION! COVER INTERLOCKS ARE PROVIDED FOR * * * * YOUR SAFETY. DO NOT DEFEAT THEM. THE VOLTAGES PRESENT * * * * INSIDE THE AMPLIFIER COMPONENTS ARE LETHALLY DANGEROUS! * * * ***************************************************************** Page 3 GENERAL DESCRIPTION Indicator lamps show when power, plate, and drive are applied. Metering left to right is filament volts(0-10vac), plate volts (0-10Kvdc), plate current(0-1adc), output power(0-300 and 0-3000 watts forward; 0-300 watts reflected; SWR forward and reverse). Drive must be reduced to this amplifier to assure legal operation inside the amateur bands. The amplifier can operate class C, B, AB2, or AB1 depending on Q point (idle bias) setting. In standby the 4-1000A is biased beyond cutoff and its output grounded to assure maximum receive noise floor. The unit re- quires well regulated 208 or 240 volt line capable of 25 to 30 amperes. A separate circuit is recommended, using #10 (#8 for runs in excess of 25 feet). The boost transformer must be wired in for 208 volt operation; the power trans- former in the plate power supply must be rewired for 120 volt operation. 120 volt operation is not recommended. See page 3 of schematic diagram. A remote power supply is utilized to save table space and for safety considerations. R. F. cage and power supply are fully power interlocked as to prevent the plate power supply from energizing with certain cover panels removed. The unit uses an EIMAC 4-1000A (8166) in a grounded grid configuration. Input pi-networks are used to match 50 ohm exciter output to the 110 ohm tube input impedance as well as to assure maximum power transfer with lowest intermodulation distortion. The input characteristic is low 'Q' providing less than 2:1 SWR on all parts of all amateur bands. The plate power supply provides 6000 volts dc at up to 1 amp with 10% regulation. Vacuum variables and vacuum changeover relay allow the use of very high voltages while keeping the R. F. cage physically small-17" wide, 13" deep, 12" high. The output circuit is a pi-network to transform the 5500 ohm output impedance to 50 ohms with a design 'Q' of 12. Extra loading capacitance is switched in on 80 and 160 meters. The unit has a built in wattmeter that reads RMS watts. The SWR function allows the wattmeter to function as a SWR meter by first adjusting the full scale meter deflection, then reading SWR directly. It is impossible to key the amplifier with plate voltage off or during plate start up sequence. Lack of filament voltage precludes operation of the bias supply. The following is a description of the automatic plate start up sequence: With Plate switch on and Control switch on the Power switch is turned on. T1 energizes lighting filament, energizing relay and bias supplies (through cover microswitch.) Three seconds later (filament warm up time) plate relay #1 energizes sending prestart signal to plate power supply prestart relay #2. The prestart relay energizes the plate transformer T3 through two 2.5 ohm 40 watt resistors in series with the 240 volt primary winding of T3. 3 more seconds elapse as the plate Page 4 voltage builds to 2/3 nominal thus limiting the current in the plate supply diode string to a safe value. Finally, plate relay #3 energizes, closing the main contactor relay, fully energizing the plate supply by shorting out the prestart resistors. Extra contacts on the main contactor complete the keying circuit back to the R. F. cage, allowing the amp to be keyed. The above sequence take from 5 to 7 seconds. The relays are arranged so that the slightest power inter- ruption (20 ms) results in the immediate deenergization of the plate power supply. The entire prestart sequence must repeat before plate can be reenergized. The sequence would start automatically should power come back on later. The above described sequencing is designed to protect the silicon diode string in the 6000 volt supply. Try turning the amp off and on as fast as you can with the Power switch to see how the protection operates! Grid current metering is not provided since it is unlikely that grid dissipation will be exceeded with 6 to 7Kv on the plate. With 10 years' operation no tubes have been ruined or suffered from reduced emission. 'Q' point bias is derived by the cathode current drawn through a selected number of forward biased silicon diodes. This biasing method provides exceptional linearity since the bias supply is as 'stiff' in regulation as the plate supply. Many engineering problems were encountered due to the greater than one octave frequency range of this amplifier. The bandswitch is designed to ground the cold end of the plate tank coil on 40 and 17 meters to move tank self res- onance away from the operating frequency. The plate RFC #2 is a two section choke. The 160uh lower section is used only on 80 and 160 meters and is shorted out by a relay on all other bands to prevent self destructive series resonances in RFC2. The 80uh top section is sufficient for 40 meters and up; both sections together provide 240uh at 80 and 160 M. The 4-1000A is a difficult tube to cure of parasitics in the 95 Mhz range because of its high output capacitance, its ability to operate at full output to 110 MHz, and its failure to achieve self neutralization above 20 MHz. The use of the low 'Q' nichrome series trap in the cathode cir- cuit is key to stable operation. The use of nichrome wire in the 40ph plate parasitic trap coil hairpin is key to reliable high power operation at 28MHz. Substantial tank circulating current flows through the tube output capacitance (in addition to C3) on 28 MHz necessitating a minimal value for the plate parasitic trap coil, while still maintaining amp- lifier stability, if reasonable efficiency is to be achieved. Nearly 50 watts is dissipated in the parasitic suppressor globar on 10 meters in c.w. operation. Plate efficiency suffers on 10, 12, and 15 meters (a low of 50% on 10) because of the above design limitations; however the amplifier still provides nearly 12 db gain. Prolonged c.w., RTTY, and key down tuning at over 1500 watts rms output above 25MHz should be avoided. Page 5 CONNECTION TO EXCITER/TRANCEIVER Using 50 ohm coax connect driver/transceiver to amplifier input connector. Plug in octal power supply control cable. Connect Amphenol HN high voltage connector to amp; make sure it's tight. Run at least #8 ground wire to ground binding post. An adequate earth ground is essential. Connect Amphenol 7 pin connector to power supply. Plug power supply into 240 volt outlet. Connect amplifier to load through at least RG8 coax. Connect driver/transceiver keying circuit to amplifier; requires a 'make' contact to ground for keying. Connect driver/transceiver ALC line to amp if desired. Plug amplifier into 120 vac. Make sure amplifier is level. TUNING PROCEDURE Turn on amplifier power and plates; verify plate voltage is on. Turn control switch off. Load driver/transceiver into desired load. Verify that the load is less than 2:1 SWR, using the wattmeter/SWR meter. 2:1 SWR is 11% reflected power. If greater than 2:1 SWR exists correct it before proceeding. Set bandswitch to desired band. Preadjust turns counters as follows: BAND PLATE LOAD Note: 160M 0720 to 0870 0460 "LOAD" presets 80M 0970 to 1080 0330 are for a 50 ohm 40M 1170 to 1190 0210 resistive load at 20M 1290 to 1300 0640 center of band. 17M 1325 0680 15M 1335 to 1350 0790 12M 1300 0750 10M 1360 to 1500 0900 Page 6 Set Wattmeter to 3000 fwd; turn on control switch. Set exciter/tranceiver for low power c.w. operation. Key exciter/transceiver into amplifier; note changeover relay operating. Quickly resonate PLATE control for maximum output on wattmeter. Retouch driver tuning and loading if necessary. Increase power and retouch amplifier "PLATE" and "LOAD" for maximum output. DO NOT run amplifier key down off resonance at maximum power as damage to the 4-1000A may result. 4-1000A should be medium orange at full power output. Avoid full power tune ups on 10M of over 15 seconds duration. Reduce exciter/tranceiver mike gain and/or carrier level to legal limit. Switch exciter to desired mode and your on the air! WATTMETER ADJUSTMENT Adjustment of the null circuit and the meter multipliers should only be attempted with the proper equipment. This consists of either a directional wattmeter of known accuracy or an accurate ohmmeter, SWR bridge, RF ammeter, and dummy load. The null adjustment rarely needs adjustment; if adjustment is required, remove R. F. cage top cover. Dismount the R. F. head from the rear panel. Using exciter power on c.w., load up into dummy load on 20M. Set the wattmeter switch on 'SWR, ref." With exciter power on, advance the SWR sens. control until meter deflection is observed. Using an insulated screwdriver or diddle stick, adjust the trimmer in the R. F. head for minimum meter reading. Reverse the coax cables to the R. F. head. Set the wattmeter switch to "SWR fwd." Null the other trimmer as outlined above. This completes the adjustment. Reconnect coax cables and remount R. F. head. Jumper the cover microswitch and tune up the linear to 300 watts as outlined in tune up procedure. 300 watts should be as measured on external wattmeter or R. F. ammeter in series with dummy load of known resistance. Set the linear wattmeter switch to "300 fwd". Adjust the 300 fwd pot on the right side of the chassis for full scale deflection on the linear wattmeter. Set the wattmeter switch to "3000 fwd." Tune up to maximum power, but not more than 3000 watts as shown on the external metering. Adjust the 3000 fwd pot to read whatever power is indicated by the external metering. Reverse the leads on the R. F. head. Set the wattmeter switch to "300 ref." Adjust the output power to 300 watts as indicated on the external metering. Adjust the 300 ref. pot for full scale reading. Correct the R. F. head wiring and remove microswitch jumper. Replace top cover. This completes the adjustment. Page 7 BIAS OR 'Q' POINT ADJUSTMENT Adjusting the 'Q' point of the tube varies the class of op- eration. Turn on the amplifier power and plate voltage. Key the amplifier without drive. Adjust switch on the rear apron for a plate current of: 120 - 140 ma class AB1 100 - 120 ma class AB2 80 - 100 ma class B 40 ma class C This completes the adjustment. INPUT CIRCUIT ADJUSTMENT Load up amplifier into dummy load on 1900 KHz c.w. Reduce power to 1000 watts output. Using small long screwdriver, adjust 160M slug through top cover for minimum driver SWR. Slugs are inside top cover behind the wattmeter instrument. DO NOT touch the tank coil or the 4-1000A plate circuit! Reload amplifier near band edges and recheck driver SWR. It should be possible to center the 2:1 passband over the entire band. Top cover MUST be left in place on 160M, 15M, and 12-10M bands since plate tank tuning is affected by top cover placement. Repeat adjustment procedure in the center of each band. Adjust 12-10M slug at 28.00 MHz. This completes the adjustment. FILAMENT VOLTMETER ADJUSTMENT Unplug the plate power supply. Remove the top cover of the R. F. cage. Remove parasitic suppressor, chimney, and 4-1000A from its socket. Connect and accurate ac VOM or DVM to the 2 tube socket pins closest to the front of the amplifier. Replace tube in socket being careful to maintain VOM probe contact; neither probe can touch ground. Turn on power switch and adjust the filament voltmeter pot (located under the input circuit sub chassis) until both instruments read the same voltage, about 7.6 vac nominal with tube lit. This completes the adjustment. Remove probes, replace tube, chimney, parasitic suppressor, top cover, and finally plug in the plate power supply. CURRENT METER ADJUSTMENT Unplug the plate power supply and remove the right side cover. Remove the R. F. cage top cover. Connect a 1.5 volt battery in series with an accurate milliameter OR a metered current source capable of 500madc across the 3 ohm 125 watt green re- sistor that sits vertically near the diode string in the plate power supply. Adjust the current meter adjustment pot (located under the input circuit sub chassis) until identical currents are read on both instruments. Use proper polarity. This completes the adjustment. Reinstall all covers and plug in the plate power supply. Page 8 PARASITIC TRAP ADJUSTMENT Completely disconnect R. F. cage. Remove top cover. Unhook parasitic suppressor, remove chimney, and remove 4-1000A. Remove small phillips screw on top of blower flange between blower and back panel. Remove small phillips screw between rear of tube base and chimney (if they were installed). Remove flat head machine screw in copper strap on top of chassis directly forward of screw #2 above. Turn amplifier upside down. Remove bottom cover. Remove pressurized sub chassis. Unsolder nichrome trap coil from tube pin and solder to #14 bus wire immediately adjacent. This bus wire is grounded. Turn unit right side up. replace tube in socket. Preset amplifier bandswitch, plate, and load controls for 12-10M operation. Unsolder plate lead from top of plate RFC2. Reconnect parasitic suppressor to tube. Using a grid dip meter, determine the parasitic resonant frequency near 95 MHz by finding the dip on the parasitic suppressor near the 4-1000 plate cap connection. Turn the unit upside down. Using the same dip meter and same frequency found above, adjust the parasitic trap capacitor for resonance. This completes the adjustment. Carefully resolder trap coil onto tube pin. Replace pressurized sub chassis and bottom cover plate. Turn unit right side up. Resolder plate wire to RFC2. Avoid sharp pointed solder joints. Replace tube, chimney, plate cap connection, and top cover. MISCELLANEOUS NOTES The relay and plate supplies are full wave bridges. The relay supply is unfiltered d.c. to improve regulation. All dial lamps and indicators are NE51s. A whisper fan is located in the plate power supply to cool the bleeder resistors. The 10 and 12 meter bandswitch setting is optimized for 10M however satisfactory output and input SWR results can be obtained on the '10-12' bandswitch setting down through 24.0MHz. The selected nichrome dropping resistors in the filament circuit are chosen to provide 7.60 vac at the tube pins with 120 vac applied to the primary of T1. Since the filament voltage can be from 7.125 to 7.875 vac (+-5%), the chosen value allows the ac line voltage to fluctuate between 113 and 124 vac without detrimental effect on the 4-1000A. The r. f. cage blower is rated at 160 cfm; tube requires 35 cfm. The blower motor dropping resistor is designed to reduce blower speed and noise while maintaining adequate air flow. The ALC output becomes more negative with increased drive. THE HIGH VOLTAGE IS LETHALLY DANGEROUS! ! THE TUBE EMITS SOFT X-RAYS WHEN OPERATING AT FULL POWER! ! KEEP COVERS IN PLACE AND USE EXTREME CARE WHEN TESTING WITH COVERS REMOVED! ! Page 9 INPUT COIL TABLE 50 ohms to 110 ohms 'Q'?2 BAND C1 L1 C2 160M 1820pf 32t #25 close wound 1360pf 80M 910pf 16t #25 close wound 750pf 40M 780pf 9t #20 close wound 470pf 20M 670pf 6t #16 close wound 470pf 17M 430pf 5t #18 close wound 3/8" form 350pf 15M 305pf 4t #16 close wound 267pf 12-10M 200pf 3 1/2t #16 spaced to 1/2" long 250pf all coil forms are 1/2" dia (ex. 17M) Miller 4400 series ceramic with tunable slugs OUTPUT COIL DETAIL AND PI-NETWORK DESCRIPTION The output tank is made up of three sections. The 12-10M coil is 5 turns of flattened 3/8" copper tubing 2 1/2" in dia. and 5" long. The center section is a PI-DUX 195-2 with the 10M coil removed. The 160M end section is 21t of #12 3" in dia. and 31/2" long (a piece of B&W 3033 coil stock). On 40M and 17M the coil cold end must be grounded to move output tank coil self resonant points away from the operating frequency. Plate design impedance is 5500 ohms. 'Q' = 12. All tank components are silver plated. BAND C3 L2 C4 160M 215pf 38.0uh 1800pf 80M 112pf 18.0uh 875pf 40M 56pf 10.5uh 435pf 20M 24pf 6.0uh 220pf 17M 22pf 4.5uh 200pf 15M 19pf 3.4uh 150pf 12-10M 21-14pf 2.0uh 130-115pf Taps are moved for maximum efficiency at 2000 rms watts output 12M-10M 15M 17M 20M 40M 80M 160M 5t + 2t + 2t + 2t + 5t + 9t + 21t 2 1/4"dia 1/4"dia 1/4"dia 1/4"dia #8 #8 #12 3/8"flat tube tube tube wire wire wire tube 1/2"long 1/2"long 1 3/4" 2"long 2 1/2" 3 1/2" 5" long long long long Page 10 BIBLIOGRAPHY The 4-1000A in Grounded Grid Larry Kleber K9KLA July, 1963, QST pp 29-34 A Power Supply for That Big Linear Amplifier Carl Smith and Doug Demaw W1CER (W1FB) December, 1969, QST pp 41-43 Some Notes on the Design and Construction of Grounded Grid Linear Amplifiers Doug Blakslee W1KLK December, 1970, QST pp 22-32 Care and Feeding of Power Grid Tubes Laboratory Staff, copyright 1982 Varian-Eimac 301 Industrial Way San Carlos, CA 94070 Putting the SB200 on 160 Meters Stafford and North KG2M November, 1987, QST pp 32-35 Technical Correspondence, RFC Design Jay Bennett AA6GK June, 1988, QST p 50 Technical Correspondence, Stable High Voltage Metering December, 1988, QST p 43 Improved Anode Parasitic Suppression for Modern Amplifier Tubes Rich Measures AG6K October, 1988, QST pp 36-39 Calculating Power Dissapation in Pasasitic Suppressor Resistors Rich Measures AG6K March, 1989, QST pp 25-28 Adding 160-Meter Coverage to HF Amplifiers Rich L. Measures AG6K January, 1989, QST pp 23-28 QST is published by: The American Radio Relay League 225 Main Street Newington, Ct 06111 Page 11 Page 12