Homebrew TWT Power Supplies

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Imogen Anderson
5 years ago
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1 14 th International EME Conference Dallas-Ft.Worth, Homebrew TWT Power Supplies Gerald Williamson K5GW Al Ward W5LUA August 13,

2 Non-Suppressed TWT B1 Fil V Adj FIL/AIR HV - PSU + R1 HV RY Input Helix I Trip TWT Output Most of the cathode current must flow to the collector Must minimize current that flows to the helix Proper focusing of the beam minimizes helix current and maximizes power output. Filament power supply at cathode potential w.r.t. ground. Must use HV relay in secondary to start tube in less than 100msec can not wait for cathode power supply to charge any capacitance otherwise tube will be out of focus and current will intersect helix could destroy tube if helix trip-out circuit not used. R1 used to limit cathode current in case of internal arcing. 2

3 Using the Anode to control TWT B1 Fil V Adj FIL/AIR HV - PSU + R1 2M ohm Anode/Grid Input Helix I Trip HV RY TWT Output Some TWTs have a grid or an anode to either modulate the cathode current or to be used as a means to turn TWT on and off quickly. When the anode is at cathode potential, the TWT is turned off. When the anode is at helix or ground potential, the TWT is turned on. 2M ohm resistor keeps anode at cathode potential until HV relay switches anode to helix potential. 3

4 Suppressed Tube - Operating the below Helix Potential B1 Fil V Adj FIL/AIR HV - PSU + Helix I Trip 4.4kV 2M ohm Anode/Grid HV RY TWT Input 4.4kV 2.7kV Output R1 1.7kV Typically can be operated at about 60% of Helix Potential Simplest but not best approach is to dissipate the extra power in R1 40% of the power is then dissipated in series dropping resistor R1 4

5 Using dual supplies for Helix and Fil V Adj B1 FIL/AIR HV Helix - PSU + 4.4kV 2M ohm Anode/Grid Input Helix I Trip HV RY TWT PSU kV R1 Output Using separate supplies minimizes high cathode to collector potential when no current is flowing could damage TWT Helix power supply supplies only a few ma of current for the helix power supply supplies high current for the collector. R1 still nice to have to minimize the big bang effect of internal TWT arcing only need maybe 500 ohms for a voltage drop of 150V at 300mA of collector current 5

6 The K5GW Approach - Using Power Supplies in Series B1 Fil V Adj FIL/AIR HV Helix Adj - PSU + Helix - PSU + Ccol R1 Chelix HV RY 2.7kV 1.7kV TWT Input Output Helix I Trip Enclosure out at Feed A lot of high power tubes either do not have an anode or it is internal connected to the helix/ground requiring the use of a HV relay in the cathode to turn the TWT on. supplies 2.7kV Helix supply is piggy backed or in series with the collector supply upping the collector by another 1.7kV and then having its return to the helix through the trip circuit to ground. 6

7 120VAC Schematic Diagram TWT HV PS 20A.01ohm see text Ry1 Rstby Ry2a Rstby Ry2b T4 T1 T2 T3 8 x 470uF/450V & 270K/3W IuF 50uF/10V Rcal Ic Mon IcTrip M 4x1N5408 Diodes 500 ohm/200w M HV RY Ry3 12 x 470uF/450V & 270K/3W Rcal 100 ohm IhTrip T1 is a 2500vrms transformer from an AL1200HF amplifier to supply collector current. T2 is a used microwave oven transformer used to boost the collector voltage high enough for the helix A variac at T4 is used in the primary to set the helix voltage. Rstby in series with T1 and T2 are used to lower the voltages during standby. T3 samples current drawn from ac lines which is proportional to collector current Rcal used to calibrate collector current meter. 100Ωresistor used to sample helix current 1N5408 diodes protect meter circuit in event of internal TWT arc over. 7

8 AC & TR Control & Trip Circuits 120VAC Input Neutral 120VAC to TWT Air/Fil 3A Air/Fil On SW1 T5 1000uf/50V Ry4 n/c Trip Ind 510 Ry5 Trip Ind HV On SW2a 510 Ry1 Ih Trip Threshold Trip Adj 150 ohm TIP120 1K 1K 1K n/o n/c Reset Trip Ic Trip Threshold Trip Adj 1K 1K 150 ohm n/o Reset Trip TIP120 1K n/c HV On SW2b Ry2 Ry3 XMIT/PTT 28VDC Helix and current trip circuits provide TWT protection and indication of fault. Must be manually reset with push button switches to regain TWT operation. 8

9 Ek HV Monitor Ec 16 x 250K Cal Cal 10K M Ek 2 - Eh(boost) 3 - Ec (Ek-Eh) 16 x 250K Cal 10K Clarification from the paper in the proceedings Position number 1 does measure the Ek which is the cathode to helix voltage, position number 2 measures Eh which is actually the helix boost voltage, and position number 3 measures the difference Ec which is the collector voltage. Approximately 1000:1 resistive voltage dividers are used to safely sample the voltages at the cathode and collector w.r.t ground. 9

10 Completed TWT Power Supply Outlet fan Inlet fan and filter 10

11 Internal Views of the Completed TWT Power Supply 11

12 TWT Cooling Assembly Heat Sink Blower Dayton 1TDR6 rated for 110 CFM 12

13 W5HN Internal Views of the Completed TWT Assembly Air filter from a shop vacuum 13

14 W5HN Various High Power TWTs Occasional gift from TSA when carrying one of these in your checked luggage 14

15 W5HN Summary The techniques described here have been used successfully with high power 200 watt plus tubes at K5GW and the echoes are very nice! Any Questions? 15

The ETO-Alpha 89 ETO-Alpha 89

The ETO-Alpha 89 ETO-Alpha 89 ETO-Alpha 89 The 89 was produced from 12/92 to 9/2000, 408 units were built during this time. These units were much like the 86, but with many updates and refinements. The 89 uses a pair of 3CX800A7 triodes