CTR AL811 Manual Download Page 16 | Manualshive

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CTR AL811 Manual Download Page 16

16

For easy soldering, pre-form D16 leads as shown. Also pre-tin them:

Figure 24 D16 form leads

Zener Diode Bias

There is no question that using as much positive cathode bias as possible, within limits of IMD,
makes the tubes run cooler. These graphs show bias means more than drive power to tube
dissipation:

Figure 25 Drive vs. Dissipation for various conditions

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Summary of Contents for AL811

Page 1: ...ours 105c rated electrolytics 2 four improved bleeder equalizer resistors 3 one large 6A grid meter protection diode 4 four 499K 1 1kV rated two watt temperature stable meter multiplier resistors These resistors also correct a slight meter error Protection Kit 811KP 1 three application tested GDT tubes 2 one large 6A meter protection diode 3 one 100k 2 watt resistor 4 two 3 9V 5 watt Zener diodes ...

Page 2: ...ntenna relays are activated by grounding the RLY jack Feed an antenna analyzer into the RF input or output jacks and listen with a radio on the other port With the amplifier on 10 or 15 meters adjust the analyzer and receiver to the same frequency Adjust the PLATE and LOAD for maximum signal Now you can safely vary flapper plate positioning for minimum signal level The best flapper setting is the ...

Page 3: ...retches the pulse out into a several mS long series of lower level oscillations below the band selected The pulse can then make it through the tuned input much like a brief high power transmitter of a few hundred watts into the radio Worst case peak voltage level is an arc while on ten meters while worst case pulse length is on 160 meters The red line is the primary damaging high frequency arc pat...

Page 4: ...son never used This prevents a weak popping noise in your receiver from intermittent gas tube ionization with some GDT s and tubes 6 Supplies an additional GDT if you want to further clamp the RF input line to the input circuit 7 You should remove MOV s if they are defective or if they are readily accessible MOV s do not add anything worthwhile in protection and MOV s are failure prone They are to...

Page 5: ...emove resistors If you plan on dropping the back panel do this shaft step first The AL 811 three tube does not require dropping the back panel just to install GDT s or do most changes GDTs in the AL811 three tube are installed as shown here ...

Page 6: ...ront screw ONLY If you remove the rear screw you will have to re index the rear switch wafer Refer to Fig 4 Figure 5 band switch shaft Remove the side rails on each side Fig 6 Remove the screws and pull the rear panel off the shaft Do not damage or rotate the blue plastic input switch on the input circuit board Once you have the panel back and off the shaft lay the panel down as in Fig 6 You can n...

Page 7: ... without removing any wiring with the exception of output coax Figure 7 properly wired back panel dropped Note Incorrectly wired panels will not drop without unsoldering multiple transformer wires and perhaps coax and other leads It s advisable to take a picture of the panel with wires attached to aid in reassembly of the panel Be careful unsoldering leads Leads are accessible through a plate on t...

Page 8: ...ctly wired panel The transformer leads are too short to allow the panel to fully lay down and must be unsoldered for input board or tube chassis service Figure 8 Figure 8 wires too short After rear panel removal remove any MOV s They will be located on the circuit board right down by the fan MOV s are sometimes blue They will be present along with capacitors Refer to Figs 9 10 11 to help identify ...

Page 9: ...9 Figure 10 capacitors Figure 11 MOVs Remove MOV s do not remove capacitors Generation I board ...

Page 10: ...tor In these amplifiers the 100K 2 watt resistor goes from anyplace on the filament system to chassis ground Gen II board Look for the small capacitor near dual relays Fig 13 and remove it if installed The string of 6 large forward connected rectifier diodes adds about 4 volts of bias Figure 13 Gen II input board ...

Page 11: ...ave MOVs Figure 14 Gen III and later input boards This is the ideal working position for all back panels This is a correctly wired back panel The back panel easily slips backwards off the switch drive without any wire removal This is a two relay board the two black relays to the right side Notice the string of rectifier diodes used for bias running along the black filament choke Figure 15 All unit...

Page 12: ... switch damage and prevent expensive broken switches Figure 16 All units break or radius shaft rear edge Remove the tubes the terminal strips and lugs in these locations and disconnect the two orange 1000 pF high voltage blocking capacitors that go between the RF parasitic board and plate choke Unsolder these capacitors at the end that solders to circuit board above the Plate Tune capacitor See fi...

Page 13: ...atsink compound and proper hardware 4 40 machine screw with lock washer and nut to mount the resistor The resistor connects across the neutralizing capacitor Fig 19 Ground the tube grids directly using solder lugs provided in the kit and solder the GDT s in Fig 18 Figure 19 add GDTs AL811H only 811 was fig 4 Check all the solder connections carefully Inspect the plate choke If the plate choke has ...

Page 14: ... resistors they should be changed The sand or tan bleeders have proven to be failure prone When they fail they ruin all four electrolytic filter capacitors A 50k to 100K higher reliability resistor of suitable wattage must be used I include suitable resistors and superior filter capacitors in the 811KS kit The small meter protection diode on the very center far right below the ferrite bead gets ch...

Page 15: ...ive This diode allows the any arc energy to get from the chassis to the capacitor bank negative harmlessly bypassing meters There is plenty of room to solder The large rectifier diode in this kit replaces D16 D16 is located near the tank coil The kit diode has thick leads It can lay solder on top of the board It does not need to fit through holes Refer to Figures 21 22 and 23 Figure 23 Meter and H...

Page 16: ... D16 form leads Zener Diode Bias There is no question that using as much positive cathode bias as possible within limits of IMD makes the tubes run cooler These graphs show bias means more than drive power to tube dissipation Figure 25 Drive vs Dissipation for various conditions ...

Page 17: ...ng over 65W is over the tube rating The diodes can be soldered in by cutting the white wire near the fan Strip both ends slide large heat shrink over the white wire well away from the diode s Make hook leads in the diodes Crimp and solder them to make connections Use either one or two diodes as required Figure 26 preparing and connecting Zener s This kit also includes a small 100K 2 3 watt metal o...

Page 18: ... intention in revised boards to supply 24 to 30 Vdc as a standby bias offset reference There is a pick point for this reference on the later boards The 100K 2W resistor connects between that 24 point and any nearby easiest accessible point of the filament winding The tap point I provided for bias or accessory use can be identified by looking for two small rectifier diodes near one of two small ele...

Page 19: ...point when we were having problems with some early Chinese early 811 tubes Figure 28 100K 2W resistor location A Early two relay board with 24V point for resistor Figure 29 100K 2 watt resistor location B Figure 30 Zener location Note Zener band is toward the transformer diode is in the cooling fan air stream This unit has the 100K resistor elsewhere ...

Page 20: ...all ferrite bead wound with wire It adds an additional ten ohms of surge resistance over the 8 ohms of the RF plate choke and 4 ohms of the filter capacitors This resistor provides almost 50 reduction in worst case current surge The small ferrite core choke must be removed to install the surge resistor since that resistor s inductance replaces the ferrite choke in RF function ...

Page 21: ...bead HV choke Figure 32 form resistor leads to surface solder See the supply kit below for resistor mounting whether you have the supply kit or not The 811KS supply kit that has solder in 500V long life high temperature capacitors These capacitors are more than enough capacitance to get over the voltage filtering and regulation ...

Page 22: ... of the kit parts offer an improvement over factory parts I suggest surface soldering parts As long as you make a good solid electrical joint with properly flowed solder the joint will have more than enough mechanical strength to hold components To install the capacitors and resistors clear the board of all the original parts you intend to replace Clear any holes where you want to mount with the l...

Page 23: ...atch for shorts or accidental close contact This is high voltage Figure 34 install new PS parts Most parts need preformed or prepared lead lengths and bends See the following suggestions Figure 35 Pre form and pre tin leads ...

Page 24: ...24 Pre tinning leads aids soldering but be careful pre tinning through hole leads Through hole leads may need hot wiped of excess solder using a wet paper towel Figure 36 Cut and preform leads ...

Page 25: ...screw 12 Figure 18 811H remove bottom screws 13 Figure 19 add GDTs AL811H only 811 was fig 4 13 Figure 20 reglue choke all units 14 Figure 21 Replace sand color bleeders Replace diode 14 Figure 22 Metering and power supply 15 Figure 23 Meter and HV Component Locations 15 Figure 24 D16 form leads 16 Figure 25 Drive vs Dissipation for various conditions 16 Figure 26 preparing and connecting Zener s ...

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