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Viking Valiant - No grid current




 
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Author Topic: Viking Valiant - No grid current  (Read 1380 times)
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WZ8J
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« Reply #25 on: September 18, 2017, 10:25:00 PM »

No,
The exciter has no effect on the buffer meter reading. Nor does it effect the oscillator meter reading.
I will take the aluminum cover off tomorrow and check out the contacts on the band switch.
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WZ8J
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« Reply #26 on: September 19, 2017, 05:17:41 PM »

I think I figured out the cause of the lack of grid current. There was a capacitor from the control grid (pin 5) of one of the 6146's to the shell (ground) on the 5763. I could not find this cap on the schematic, so I removed it.
Lo and behold, suddenly we have grid current and I can tune it with the exciter.
Well, that joy lasted for a few minutes until I thought I heard a little arc and smelled a rank odor and then a bit of smoke. I fear it may be coming from L-43.
Of course I turned it off immediately.  Undecided
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N1BCG
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« Reply #27 on: September 19, 2017, 08:38:37 PM »

Yikes.

Can you post a pic of the cap you removed and where it was? I'm not clear on what you meant by the shield of the 5763. Also, L43 is the choke in the high voltage power supply. If that smoked then you're drawing tremendous amounts of current.

Lots of things need to be checked before any high voltage is applied...
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DMOD
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« Reply #28 on: September 20, 2017, 12:55:32 PM »

I think I figured out the cause of the lack of grid current. There was a capacitor from the control grid (pin 5) of one of the 6146's to the shell (ground) on the 5763. I could not find this cap on the schematic, so I removed it.

Lo and behold, suddenly we have grid current and I can tune it with the exciter.
Well, that joy lasted for a few minutes until I thought I heard a little arc and smelled a rank odor and then a bit of smoke. I fear it may be coming from L-43.
Of course I turned it off immediately.  Undecided

It doesn't appear your V8 Clamper tube stage is working properly, if the current draw was due to the Finals'.

Were the 6146's checked in a tube Tester? One of more may be faulty.

As Clark said, make sure the LV and the exciter section are working before applying HV.

It is always a good idea to compare the circuitry to the schematics before beginning any mods or upgrades, even before applying any voltages.


Phil - AC0OB
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WZ8J
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« Reply #29 on: September 23, 2017, 07:40:00 PM »

The weird thing is that I have not switched on the high voltage. Only turned the Exciter control on low voltage mode. I did not try to tune up the rig. Never got that far before I smelled whatever is heating up.
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N1BCG
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« Reply #30 on: September 23, 2017, 10:11:54 PM »

If something is heating/burning up then it's time to switch to "safety mode". A simple system involves taking a short three conductor extension cord and intercepting the black (hot) lead. At that point, connect a porcelain lamp socket (like you'd find in a closet) and insert a 150 watt bulb. The Valiant plugs into this cord and the cord plugs into the wall.

Basically, this circuit acts as a current limiter so even a direct short would merely illuminate the bulb fully. A 150 watt bulb will only partially light with the Valiant on (but not keyed) and it makes finding short circuits much easier with less risk to the components.

Of course, all of your voltages will be slightly lower but you'll still be able to get some drive for test purposes. I've found this series bulb circuit invaluable for "first time lightups" of all kinds of gear, particularly in conjunction with a variac.


* IMG_5659.JPG (2022.75 KB, 3024x4032 - viewed 33 times.)
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WZ8J
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« Reply #31 on: September 25, 2017, 03:01:36 PM »

Now there's a station accessory even I can build!
Very clever. I will definite put one of these together.
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KB2WIG
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« Reply #32 on: September 25, 2017, 03:25:03 PM »



Try mine------ it has a switch... much more attractive than that one



klc
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What? Me worry?
WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #33 on: September 27, 2017, 11:29:31 PM »

My Valiant II crapped out.
No grid drive.
Buffer, yes.

Turned out a badly acting 5763 drive tube.
Works fine now...

Might be the problem, might not.

                  _-_-
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WZ8J
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« Reply #34 on: October 01, 2017, 11:25:55 AM »

Again, just want to thank all who provided helpful comments and guidance.
Here's the latest on Val-ain't:
I took someone's suggestion and started checking the wiring vs. the schematic, but then also found the build instructions for the kit on line. This was a great help to confirm my reading of the schematic.

Turns out that whoever installed new HV filter caps hooked them up incorrectly. I fixed that and tried it again, this time with the 3B28's removed. No smells, no smoke and buffer, oscillator and grid currents look good.
I then installed the HV rectifier tubes and tried it again (low voltage only) and still no problems, all seems okay.

So, I guess the next step is see if I can tune up the rig....stay tuned.

Sure learning alot in this process, but that was the intention of getting a fixer-upper.
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N1BCG
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« Reply #35 on: October 01, 2017, 08:33:40 PM »

That sounds great! Incorrectly installed caps in the HV supply would certainly get your attention on transmit. Wondering now if the previous owner made claims of the rig "running great". Hmm.

You might be able to try it out, quickly, first with the meter set to Plate and then again set to Mod. The Drive control should be fully counterclockwise.

If the current goes full scale on Plate, the Clamper tube setting may be wrong.

The current should go to 50-70 Ma on Mod when the modulator bias is properly set.
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WZ8J
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« Reply #36 on: October 02, 2017, 06:43:24 AM »

Hey Clark,
I tried to go through the tune up process after properly installing the HV filter caps, but when I flipped the manual switch to on and the meter to plate there was no reading. A quick turn of the FINAL adjustment yielded nothing. Before I got a chance to adjust the COUPLING, I heard a "braaap" and both fuses in the line cord blew.
Hope the HV transform is okay... Huh

I had thought about going to email with this correspondence, but I am sure someone will reference this thread for leads to solve their own issues as I scoured the net looking for such clues. Or, maybe morbid curiosity will lead them here for entertainment.
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WD5JKO
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WD5JKO


« Reply #37 on: October 02, 2017, 07:42:52 AM »


I have no specific hands on experience here, but generally speaking, installing electrolytic capacitors backwards can only be fixed by replacing them with new ones, and getting the +,- correct. The ones installed before are likely toast. Electrolyte capacitors are NOT self healing.

Jim
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N1BCG
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« Reply #38 on: October 02, 2017, 07:48:22 AM »

Agreed. Check the resistance across those caps and you'll probably find a short circuit. Removing them should raise the resistance to about 20k, the value of the voltage dividervresistors across each cap.
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DMOD
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« Reply #39 on: October 02, 2017, 11:10:59 PM »



I took someone's suggestion and started checking the wiring vs. the schematic, but then also found the build instructions for the kit on line. This was a great help to confirm my reading of the schematic.

Turns out that whoever installed new HV filter caps hooked them up incorrectly. I fixed that and tried it again, this time with the 3B28's removed. No smells, no smoke and buffer, oscillator and grid currents look good.
I then installed the HV rectifier tubes and tried it again (low voltage only) and still no problems, all seems okay.



There should be no HV generated until you close the PTT circuit (KeyDown) or flip the front panel switch.

Let's hope the 3B28 filament to plate resistances saved the HV transformer.


Phil - AC0OB

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