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Title: Viking II no Mod Post by: k5kab on April 25, 2010, 12:44:00 PM Ok guys I,m close everything is holding great. Replaced the 2 pin mic jack to a 4 pin jack, tuned the radio to 250 mils of plate. Switched meter to MOD to see the idle current draw and there is NON.
Audio thru the mike and the mod meter jumps slightly but no output. I guess the key is no idle current on the mod meter. ??? Title: Re: Viking II no Mod Post by: WD5JKO on April 25, 2010, 01:22:29 PM I would check the 807 voltages underneath at the tube sockets. Specifically, look at the Grid 2 (screen) pin for somewhere around +300v when keyed up on AM, and the Grid 1 (control grid) pin for a negative voltage somewhere around -30 to -40 volts. Me suspicion is that the HV bleeder resistor may be open circuit. If this happens then the you may not have any screen voltage to the modulators. Also look at the 807's (glass) when you key up on AM. Do you see any blue inside, that might also move around when you try to modulate? If so, maybe the modulator is fine, but your issue is in the metering side of things. Good Luck, Jim WD5JKO Title: Re: Viking II no Mod Post by: N3DRB The Derb on April 25, 2010, 05:02:48 PM make sure you short the HV before touching anything....if the bleeder is shot it will sit there with death underneath for a long time.
Title: Re: Viking II no Mod Post by: k5kab on April 26, 2010, 09:51:49 PM I would check the 807 voltages underneath at the tube sockets. Specifically, look at the Grid 2 (screen) pin for somewhere around +300v when keyed up on AM, and the Grid 1 (control grid) pin for a negative voltage somewhere around -30 to -40 volts. Me suspicion is that the HV bleeder resistor may be open circuit. If this happens then the you may not have any screen voltage to the modulators. Also look at the 807's (glass) when you key up on AM. Do you see any blue inside, that might also move around when you try to modulate? If so, maybe the modulator is fine, but your issue is in the metering side of things. Good Luck, No Hv on the bottom of the 807's all the pins read -39 volts. Caps seems to be good. With the voltage divider R-13 adjusted all the way to the rear, I do get blue flicker from the 807's and 50 mil on the MOD meter but still 0 on the MOD meter at idle.I can hear a slight audio signal thru a second receiver but the audio is low about a 2-3 on a scale of 1-10. What gives ??? ??? Title: Re: Viking II no Mod Post by: WD5JKO on April 26, 2010, 11:16:43 PM No Hv on the bottom of the 807's all the pins read -39 volts. Caps seems to be good. With the voltage divider R-13 adjusted all the way to the rear, I do get blue flicker from the 807's and 50 mil on the MOD meter but still 0 on the MOD meter at idle.I can hear a slight audio signal thru a second receiver but the audio is low about a 2-3 on a scale of 1-10. What gives ??? ??? I am attaching the Vik2 schematic, and 807 tube diagram (bottom view). The filament leads are the big fat pins (1,5), so going clockwise we have pin2 (screen grid), pin3 (control grid), pin4 (cathode and g3). If all pins read -39 volts then you have multiple problems. I would take Derb's advice and before getting in there (power off), short out the HV and LV B+ to make sure the circuits are dead. Then ohm out the wiring to those sockets. The current shunt SH2 is a suspect as is the solder connection to it. The bleeder resistor R13 (20K WW with slider tap) might be open circuit. Jim WD5JKO Title: Re: Viking II no Mod Post by: WA1GFZ on April 27, 2010, 11:15:49 AM You need to adjust the slider to get the screen voltage up higher
when you tighten the screw again go a bit less than snug or it will damage the resistor and open it then you will lose your bleeder and the rig becomes very unsafe. Title: Re: Viking II no Mod Post by: k5kab on April 27, 2010, 02:47:08 PM You need to adjust the slider to get the screen voltage up higher I am almost at the very end of the bleed risistor,just to get any screen voltage. when you tighten the screw again go a bit less than snug or it will damage the resistor and open it then you will lose your bleeder and the rig becomes very unsafe. Title: Re: Viking II no Mod Post by: WQ9E on April 27, 2010, 04:59:41 PM Kill the power and pull the plug and then short the plate supply to ground. After you remove the short, measure the resistance of the plate supply to ground (where it connects to R13)-it should be around 20K. It sounds like R13 is open, another possibility is you do have to tighten the adjustable slider reasonably tight after you adjust it; otherwise you form a high resistance at the tap point.
But odds are the resistor is bad. Title: Re: Viking II no Mod Post by: k5kab on April 28, 2010, 01:54:33 PM Did more digging last night . Grid pin 2 screen 0 volts, Grid pin 1 -38 volts.
R-13 at the HV end (3 purple wires) is 710 volts, checking continuity the wires are good all the way to T-3. The purple HV wire at T3 from R13 gives me 203 volts, but 0 volts at Pin 2 keyed. Title: Re: Viking II no Mod Post by: WA1GFZ on April 28, 2010, 02:58:32 PM How about the function switch
Title: Re: Viking II no Mod Post by: k5kab on April 28, 2010, 04:43:54 PM How about the function switch What about the function switch Title: Re: Viking II no Mod Post by: WA1GFZ on April 28, 2010, 04:54:05 PM The 807 screen connections go through the function switch. Look at the schematic provided
Title: Re: Viking II no Mod Post by: ka3zlr on April 28, 2010, 05:05:32 PM And make sure the little black ground wire from the function switch that goes under the
switch and through the chassis is soldered and connected well... 73 Jack. Title: Re: Viking II no Mod Post by: N3DRB The Derb on April 28, 2010, 06:41:02 PM also heck C8 your 807 screen bypass a .5 I seem to recall thats a paper cap.
Title: Re: Viking II no Mod Post by: k5kab on April 28, 2010, 09:07:17 PM when your saying function switch, is that the cw/phone switch ?
where should this 300 volts come from I checked on one side of C-10/C-11 and found the 300v but it drops to -54 on the other side, and this is where the purple wire that gives the 300v to the 807 screen starts. So im confussed as to what component. I jumped from the 300v straight to the 807 screen an got everything running great rigging it. hahahahahahaha where is the problem wow. hahahahahahahah ??? Title: Re: Viking II no Mod Post by: WA1GFZ on April 29, 2010, 10:57:29 AM You will fry the 807s if you leave the LV supply connected directly to the 807 screens without plate voltage. This is a very simple circuit. The slider resistor sets the 807 screen voltage. This voltage connects to the 807 screens when the function switch is in the AM position. The reason the screen voltage comes off the slider is to remove plate voltage and screen voltage at the same time.
Title: Re: Viking II no Mod Post by: k5kab on May 19, 2010, 09:50:06 AM Bullz eye R-13 BLEED RISISTOR DEAD thanks guys, for pointing me right at the problem. Funny how people can tell you about the forest, but in often times you can't see it for the TREES, ??? ??? hahahah Thanks a million
Title: Re: Viking II no Mod Post by: WA1GFZ on May 19, 2010, 12:42:21 PM It was just your turn AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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