Home Back Schematic Ladder Power Supply Conecting Cable Tuned Input J Box Oil System Notes
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GS35B Theory of operation:
(line number references apply to the ladder diagram)

Power Supply 1, is a 12 VDC 10 AMP switching supply for tube filament, located inside control circuit chassis(line 7). Power Supply 2, is a 24 VDC 5 AMP switching supply for control voltage, located inside control chassis(line 7). There is also a 12 VDC power supply inside the amplifier J Box(line 6) mounted at the back bottom of the amplifier cabinet this supply powers the 3 1/8" square muffin fan, F2(line 8), that blows air through the cathode chassis and up through the tube socket to remove filament heat as the oil cooling system only removes anode heat so the cathode chassis could overheat with no cooling at all. This fan was also taken from a junk computer. F1(line 6) is a small 2"X2" CPU fan removed from a junk computer that is mounted on the outside of the control chassis to provide some airflow to keep the heat sink of the bias board cool, I drilled multiple 1/8" holes in front of the fan and again through the top cover of the control chassis directly above the bias board heat sink for cooling. F3(line 3) is a box fan 18 inches square or so with a automotive transmission oil cooler attached. P1(line2) is a little giant model 7121-6641 pump to circulate the transformer cooling oil. P1 and F3 are located in a remote location in my case in the basement/crawl space under my ham room, but may be located any convenient remote location to keep noise and heat out of your operating location, even outside if weather permits.

Power On: Power switches S1 and S2(line 3), S2 is normally the power switch as S1 is normally left in the on position as K1 main contactor(line 4) is energized via S2.
(This arrangement allows one to turn off S2 and then turning on S1 everything goes through the start-up cycle except upon completing all steps, the K1 relay energizes, however as S1 is off you get no high voltage until manually turning on S1)
Upon turning on S2 120 VAC is applied to the coil of K1 however the Neutral side of the coil for the K1 contactor must go through the n/o contacts of K2(line 3). The K2 relay is not energized until the TDR timing relay in the control circuit chassis provides a 180 second delay for filament heating. Once the 180 second delay TDR energizes, K2 energizes, K1 energizes applies 240 volts to the primary of T1 5kva 240/2400 VAC power transformer, through the R12 70 ohm 25w resistor. As this is a capacitor input DC supply it appears as a dead short to T1 initially and the voltage across the K3 coil(line 5) remains very low due to the voltage drop across R12, as the filter capacitors charge up the voltage across the K3 coil rises and after about a second K3 energizes shorting out R12. I had only a 120 VAC coil 30 Amp rated contacts rated relay to use for K3 so powered it from one side of the 240 VAC T1 primary to the center tap of T1 primary thereby providing 120VAC when at full primary voltage, if you have a 240 VAC coil relay for this purpose then the coil of K1 would go across the full 240VAC primary of T1 and not connect to the center tap. Also power supplies 1 and 2, inside control chassis have been energized, and fans F1(line 6), F2(line 8), F3(line 3), and Pump P1(line2) have been energized.
Switching Supply 1, 12 VDC filament supply, has in-rush current protection built in. The GS35B is rated at 11.9-13.3V @ 3 Amps my supply is a adjustable regulated switching supply rated 12.6 VDC @ 10 Amps. When the filament voltage reaches 12 VDC the RLS Relay(line 9)energizes and the RLS contacts apply power to the TDR relay to initiate the 180 second heater warm up time delay. This arrangement allows the filament to attain full voltage before the TDR begins its filament heating time delay. The filament supply is adjusted to supply 12.6 VDC measured directly at the tube filaments after warm up. When the TDR relay times out NO contacts 8 and 6 of TDR(line 11) close energizing RL1 relay, and the other set of NO contacts close allowing the K2 relay to energize, this arrangement allows the tube to reach full heating of the filament before applying the high voltage.
(Relays RL1, RL2, RL3, RL4, and RL5 are 1" cube size, 24 VDC relays with one spdt contact rated at 10 amps. They do not have pin numbers, on the ladder diagram everything is shown in standby, power off conditions.) When RL1 energizes its NO contacts close, RL2 will be energized providing there is not a grid overload present and that the flow switch is closed. (Line 12 of ladder diagram). In line 14/15 of the ladder diagram you will see the PTT from the transceiver/transmitter when this is closed/shorted the path from the -24 can flow to the RL2 NO contacts(line 15) (RL2 is energized by the TDR relay so if the 180 second delay has completed the RL2 is energized and those contacts are closed) then to the left to the stand by switch(line 16), If in operate position then to the left to a branch one way is to the antenna relay(s)(line 15/16) and to RL5 (line 14), these are energized immediately then the RL3 relay(line 13) energizes through the RL5 NO contacts, this is to allow the antenna relays to close before high power RF is transmitted, if no delay antenna relays can be destroyed. In lines 16/17, you will see the grid overload protection circuit, max allowable grid current is set with R6 50 K ohm potentiometer when grid current exceeded Q1 will conduct and energize OL relay(line 17) via a close contact of the standby switch being in operate, this contact shown in standby position on ladder diagram, once energized the OL relay will latch close through its own NO contacts 9 and 6 and remain latched until placing the standby switch back in standby thereby opening its contacts in line 17 and de-energizing the OL relay. A note about relay RL4, this relay is normally energized via the NC contacts 9 and 3(line 18) of the OL relay opening the NC contacts of RL4 in line 19 of the ladder diagram and thereby not lighting the red overload light until the OL relay energizes and de-energizing the RL4 relay causing the RL4 NC contacts to close. The bias is provided by the W4ZT bias board, the adjustment is made via R2 a 10K ohm wire wound pot from the front panel, it is adjusted to obtain 120ma idling grid current. This amplifier works extremely well, I get between 1200 to 1500 watts out on all bands driving it with my TS-590S. It makes almost no noise, the two small cooling fans are whisper fans and if you don't listen very close with no receiver noise you really do not even hear them. In the summer you can operate for long durations like in a contest, the amp just idles along and your area does not heat up from extra heat.

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