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Author Topic: Viking II High Voltage problem  (Read 31569 times)
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WA1GFZ
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« Reply #25 on: January 08, 2009, 03:56:34 PM »

longest post wins!!!!!!!!!
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Steve - WB3HUZ
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« Reply #26 on: January 08, 2009, 10:32:01 PM »

PHD - Piled High and Deep.
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ka3zlr
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« Reply #27 on: January 09, 2009, 05:05:47 AM »

Ok is the Posturing over... LOL...Grin

Did he get the transmitter fixed..? that's all i wana know...I got an extra Mod tranny if he needs it....Junxton Junk... Grin

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WA1GFZ
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« Reply #28 on: January 09, 2009, 08:36:10 AM »

up here in 1 land it is "piled higher and deeper"
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Steve - WB3HUZ
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« Reply #29 on: January 09, 2009, 10:23:28 AM »

Well, of course it would be, in 1 one-land.
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KM1H
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« Reply #30 on: January 09, 2009, 11:26:55 AM »

But up here its frozen solid until the spring thaw. Down below it keeps getting deeper and riper.

Carl
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WV9R
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« Reply #31 on: January 09, 2009, 07:37:50 PM »

Hi all, wow lots going on here ..well I replaced the caps and I am waiting on a rectifier tube..once I get a tube I will check the clamp tube adjustment and see what happens ..hopefully I dont let any smoke out. I'll keep everyone updated as I go ..and if you see a mushroom cloud in the direction of Chicago...hopefully it wasnt me.  hih
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Ray
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« Reply #32 on: January 09, 2009, 07:45:38 PM »

Ray,

When you get it going let us hear it on the Midwest Classic Radio Net which meets on Saturdays at 7:30 A.M. local on 3885.  Unless your tube is coming overnight I guess we won't hear it tomorrow morning  Smiley

Enjoy the snow tonight and please keep it upstate!

Rodger WQ9E
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Rodger WQ9E
WV9R
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« Reply #33 on: January 10, 2009, 10:02:17 AM »

Hi Rodger, Nope no tube yet...I'll try to keep the snow up this way, but dont want you to get sleet or freezing rain ..my son is on his way back to school down there by you. I'll let you guys know when the tube arrives and I will get on the net ..Thanks Ray
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Ray
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WQ9E
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« Reply #34 on: January 10, 2009, 10:17:34 AM »

Hi Ray,

We got the freezing rain but not enough to cause any problem except for the roads.  I am a prof at Illinois State and classes start Monday for us.  Looking forward to hearing your Viking 2.

Rodger WQ9E
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Rodger WQ9E
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« Reply #35 on: January 10, 2009, 07:44:56 PM »

Hi Rodger,
       Thats where my son is going, in his 2nd year, he's not sure what he wants to do yet, but I'm not suprised.  I told him he should check and see if there is a radio club on campus. Well hope the weathers better for you than us all week .  Ray
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Ray
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« Reply #36 on: January 10, 2009, 10:46:24 PM »

Ray,

Have him look me up sometime.  If we cannot draft him into the College of Business I will be happy to put him in touch with someone in the proper college.

Rodger WQ9E
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Rodger WQ9E
WV9R
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« Reply #37 on: January 12, 2009, 10:22:40 PM »

Hi All,  Well I was able to borrow a 5v4g tube and got the Viking II fired back up ..it tunes nicely with all of the currents as per the manual, except one, I have no modulator cathode current, the manual says, in the clamper tube adjustment, that it should be set to between 60ma and 80ma, I have none, notta, zip....down in this section all of the resistors and caps have been changed. Not sure if a mod has been done or not. I did notice though that R10 and R11 are 200 ohm, not 100 as the print shows. I'm going to download the mods , I think there were 2 of them , and see what I can figure out , if anything hihi...does anyone know what voltages I should be looking for on the pins of the 807's, I know I'm being a pain in the ass asking all of these questions, but this is really my first endeavor into this type of transmitter. Any help as, always would be greatly appreciated.  Thanks Ray
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Ray
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« Reply #38 on: January 12, 2009, 11:04:27 PM »

Ray,

Typically I would suspect a problem with the tap setting on R-13 which sets the screen voltage for the 807 modulator tubes, you should typically have around 250-270 volts appearing on the screen grids.  The fixed bias should be around -37 volts on the modulator control grids, and the plate voltage should be around 620-640 with the final loaded to rated input.

While you are checking this I would suggest doing so with the modulator tubes removed from the transmitter since you don't need them in place and you don't want to damage them.  I would suggest first measuring the control grid bias at the tube sockets (you don't need the plate/HV switch on for this and make sure it is within +/- 15% of -37 volts).  If this is good, then you need to measure the other tube potentials.  Since HV is present at so many places on top of the chassis in the Viking 2 I strongly suggest you connect your meter with all power off and then power up to make your measurement and remove power before removing your meter leads.  I would not bet my life on the bleeder resistor so after powering off and before connecting any leads wait a minute or so and then short the plate supply to ground.  Then set up and  measure the screen voltage and if it is very low then you need to find out why, whether it is simply a need to reset the tap on R-13 or if there is another issue.  If the screen is good, measure the HV at the plate caps again exercising extreme caution.

The value of R10 and R11 will have no significant impact on the resting current of the modulators.

Rodger WQ9E
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Rodger WQ9E
WV9R
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« Reply #39 on: January 12, 2009, 11:05:37 PM »

As a update:  Both of the audio mods that I found required changing the tubes out. Both of the tubes that I have a 6au6a's, so if a mod was done the tubes were not changed, does anyone know of a mod that left the tubes the same? Thanks Ray
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Ray
WV9R
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« Reply #40 on: January 12, 2009, 11:08:41 PM »

Thanks Rodger,  I also noticed it appears that someone removed the resistors in the leads going to the caps of the 807's, or was this a resistance type of wire?  Thanks Ray
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Ray
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« Reply #41 on: January 12, 2009, 11:23:57 PM »

The mods by Thomas Bonomo, K6AD, in ER mag a fews years ago, used the original audio tubes, with a phase inverter tube added as part of stage 2 mod. The ER issues are 110, 111, and 112. I am planning these changes for my Viking II when basic repairs are complete. (time? what free time!?)
Norm K7NCR
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WV9R
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« Reply #42 on: January 12, 2009, 11:31:20 PM »

Hi Rodger,  Looks like I have some other issues, On the leads going to the caps of the 807's I have 740 volts, I dont see any screen voltage, and I see two negative voltages, one in the 72 volt range and one in the 55 volt range. On the yellow and green lines of T3, I'm reading -72 volts and past R10 and R11, on one I'm reading -55 and on the other it's still -72...think I need to shut down for the night and regroup..I also measured voltage on the tap of R13 and got a negative reading there too ...I keep telling myself this is my hobby ..I enjoy this ... Grin
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Ray
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« Reply #43 on: January 13, 2009, 08:39:52 AM »

Hi Ray,

Part of the fun of the hobby is the feeling of accomplishment after you "slay the dragon" that is harassing you  Smiley

Based upon what you have found, first a couple of questions and then some suggestions:

1.  Are the bias capacitors new and near the correct value (not over 22uf for the input capacitor C13)?
2.  Are you still using a 6AL5 for the bias rectifier or has it been replaced with SS diodes?

I am assuming that the answers to 1 and 2 are yes.  If so, check the values of resistors R15, R16, and R17.  These provide the bleeder and voltage taps for the bias circuit and it sounds like 1 or more have drifted high in value since the center tap on T-3 is being fed with too high of a voltage.

Are you making the measurements past R-10 and R-11 with the 807 tubes in or out of socket?  There should not be any significant current flow through the control grid lines on these two tubes so if the tubes are in you have a tube problem and if not there almost has to be an issue with the socket, even if one of the two resistors went way up in value you should not be measuring much voltage drop since the only current flow should be through your meter.  I am assuming you are using a fairly modern meter with at least a 20,000 ohm per volt sensitivity and more likely a 10 megaohm input from a DMM.

The abnormally high HV reading combined with a negative reading on the tap indicates that R-13 is probably open (or disconnected for some reason).  Remove power from the transmitter and short the HV to ground, then remove the short and measure resistance to ground.  If it is over 20K ohms (and it is likely well over this) then your bleeder resistor R-13 is open or disconnected.

Rodger WQ9E
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Rodger WQ9E
WV9R
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« Reply #44 on: January 13, 2009, 09:02:00 AM »

Hi ..R17 is not droppingthe bias voltage at all.  I clipped on side and temped in a 4.7k, all I have and the bias dropped to about -30 volts. I'll have to check R13, but it's off to work in the snow now ..hopefully the roads are not too bad, I drive to Michigan City Indiana, right in the famed "snow belt", it can be bright and sunny here, but there it could be a blizzard if the lake effect snow machine turns on. I'll post more tonight.  Thanks
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Ray
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« Reply #45 on: January 13, 2009, 08:48:25 PM »

Heres todays update:  I replaced R17 which is suppose to be a 2700 ohm resistor, well mine tested at 110 ohms, so changed it and now I have -41 volts of bias at the 807's so thats all good. I checked around and found a cold solder joint on the 6aq5 and after cleaning and resoldering  I have 202 volts getting to the tube.  The tap on R13 still shows a negative voltage. I tested R13 and it was at 19,600 ohms.I still have no mod current or from what I can see screen voltage at the 807's. I'm seeing this schematic in my sleep ...something is not calling my name, and I hope it doesnt reach out and slap me either hihi...any suggestions would be greatly appreciated...it coming along one small step at a time.  Thanks Ray
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Ray
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« Reply #46 on: January 13, 2009, 09:30:24 PM »

Hi ..I've got a question...on the HY plate switch there are 4 wires, at least on mine. 1 is white with orange/blue trace 1 is white with silver/red trace 1 is black and 1 is orange, now where the orange wire is there was another wire that has been cut, can anyone tell me what it was and where it should be going? I cant fined the other end anywhere ..Thanks Ray
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Ray
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« Reply #47 on: January 13, 2009, 09:38:13 PM »

Ray,

Since you have high voltage but you have negative voltage on the R13 tap, either the tap is not making contact with the resistive wire on R13 (is it loose) or R13 is not connected to the high voltage.  So check and make sure that one end of R13 is connected to the HV bus, the other end is held slightly above ground by the metering shunt sh1.  The top end of R13 should have the full high voltage on it and the tap is set to provide the screen voltage to the 807 modulator tubes; it should be a few hundred volts positive with respect to ground and not negative. 

One side of SW-2 applies power to the plate transformer, the other side is used to ground the cathode of the oscillator tube V6 so that it is operational when the plate switch is on, it is also connected to the accessory plug on the back to provide a switched ground for the external VFO to activate it for transmission.
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Rodger WQ9E
WA1GFZ
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« Reply #48 on: January 13, 2009, 10:07:23 PM »

Your modulator screen voltage should measure high if the 807s are removed since there is no current through the screen dropping resistor..
Light load the high voltage will be high. Mine runs 760 with solid state rectifiers. Check the resistance of the big slider resistor. Many times someone set it too tight and broke the fine resistance wire. A negative voltage could mean it is open at the tap. be very careful if the resistor is open because that is also the HV bleeder and it will hold a charge for a while after you unplug the rig.
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WV9R
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« Reply #49 on: January 13, 2009, 11:42:49 PM »

I want to thank everyone, espically Rodger for all of the help I received. I cleaned R13 a bit and cleaned the contact on the band and now I have mod current. Cheesy I adjusted it as it says to in the manual in the procedure for adjusting the clamper tube. I'll finish the adjustment tomorrow and see what I end up with ..if it all looks good I'll put the rest of the case back on and see if I can get it on the air...if it all works out good it will be on the the Thunderbolt to see what condition it's in ..I havent even plugged it in yet ...one project at a time... Grin  I'll post tomorrow ...hopefully with good news!
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Ray
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