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Viking Valiant - No grid current




 
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Author Topic: Viking Valiant - No grid current  (Read 11852 times)
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N1BCG
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« Reply #100 on: December 28, 2017, 10:50:59 AM »

Yep, something's amiss. You should be able to get a perfect 50Z match with no reactance using expected control settings *.

Check each lug of the "turnstile" cap for resistance to ground. All should be open. Do the same for the mica caps that connect between the bandswitch and the chassis. This will locate shorted caps (most common issue). Be sure to test each of the mica's separately as some are in series.

Open caps can be found by taking a spare cap (all Valiant owners have lots of these) and bridging across each cap. Look for changes that return the control settings to where they should be.

Of course, a capacitor checker can also make fast work of this. I believe the MFJ antenna analyzer has one built in.

* I made a chart of control settings for commonly used frequencies on each band. It shows the knob settings for Drive, Exciter Tuning, Final Plate Tuning, Aux Loading, and Fine Loading. Only minor, if any, adjustments are needed when pre-setting the controls.  

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WZ8J
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« Reply #101 on: December 28, 2017, 05:04:49 PM »

Yep, something's amiss. You should be able to get a perfect 50Z match with no reactance using expected control settings *.

Check each lug of the "turnstile" cap for resistance to ground. All should be open. Do the same for the mica caps that connect between the bandswitch and the chassis. This will locate shorted caps (most common issue). Be sure to test each of the mica's separately as some are in series.

Open caps can be found by taking a spare cap (all Valiant owners have lots of these) and bridging across each cap. Look for changes that return the control settings to where they should be.

Of course, a capacitor checker can also make fast work of this. I believe the MFJ antenna analyzer has one built in.

* I made a chart of control settings for commonly used frequencies on each band. It shows the knob settings for Drive, Exciter Tuning, Final Plate Tuning, Aux Loading, and Fine Loading. Only minor, if any, adjustments are needed when pre-setting the controls.  


There was continuity between one tab on the turnstile cap and ground. That is the only cap with that condition.
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KD6VXI
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« Reply #102 on: December 29, 2017, 06:49:07 PM »

That could completely be within the tolerance of an Mfj device.

--Shane
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WZ8J
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« Reply #103 on: December 30, 2017, 05:43:47 PM »

So while I know there is an issue with the turnstile cap, I have learned that the real reason I suddenly couldn't get the plate current to be low enough on 75M was due to my installing the incorrect precision resistor I recently bought for one of the meter shunts. I had somehow managed to install the .404 ohm jobby where the .202 ohm resistor should have been. Now that is fixed and I can again safely load the rig up on 75.
I will address the turnstile cap when I get my latest shipment from Mouser.

Still needing to resolve the HV hum which seems to come from L-43. It physically vibrates. I was able to confirm this by pressing the handle of my solder sucker tool to the side of the case and can feel the vibes coming through. Tried tightening the screws but this had no effect.
 
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WD8KDG
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« Reply #104 on: December 30, 2017, 05:49:39 PM »

So while I know there is an issue with the turnstile cap, I have learned that the real reason I suddenly couldn't get the plate current to be low enough on 75M was due to my installing the incorrect precision resistor I recently bought for one of the meter shunts. I had somehow managed to install the .404 ohm jobby where the .202 ohm resistor should have been. Now that is fixed and I can again safely load the rig up on 75.
I will address the turnstile cap when I get my latest shipment from Mouser.

Still needing to resolve the HV hum which seems to come from L-43. It physically vibrates. I was able to confirm this by pressing the handle of my solder sucker tool to the side of the case and can feel the vibes coming through. Tried tightening the screws but this had no effect.
 

L-43...............I've never seen one, but:

If there are bell ends.........remove them. There is a thimble with the windings that is on the iron lamination. A wooden wedge might do the trick??

Craig
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Ham radio is now like the surprise in a box of "Cracker-Jacks". There is a new source of RFI every day.
WZ8J
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« Reply #105 on: January 27, 2018, 04:06:30 PM »

N1BCG said:
If the Valiant Oscillator switch is set to ZERO or the Mode switch is set to CW (but not keyed), a low level RF signal will be generated using just the low voltage supply. This should be clean when heard on a receiver set to AM and CW (for checking tone).

I can hear hum on the CW signal in a receiver with the rig only connected to a dummy load & with the mode on CW and Oscillator set to Zero. Hum also present on AM on the zero setting (no HV on in either case)

So does this mean the hum is originating from the low voltage supply?
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N1BCG
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« Reply #106 on: January 27, 2018, 04:35:13 PM »

So does this mean the hum is originating from the low voltage supply?

Probably, but be sure you're not getting "carrier-current hum" which is when a strong signal is re-radiated by power wires. This can cause a 60 Hz hum to be superimposed on the signal. However, using the dummy load should have prevented.

Are the LVB+ caps new?
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WZ8J
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« Reply #107 on: January 27, 2018, 05:21:04 PM »

pretty sure its not carrier current, since it is only LV low power signal.
I replaced the 15 UF 450V bias supply caps, but can't remember if I replaced them again, after the zorch incident.
I did replace both LV supply caps, and yes i got the reversed polarity correct.
I do have some new 400V 15 UF electrolytics, would it be okay to try these even if for a short test or is that too risky?
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N1BCG
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« Reply #108 on: January 27, 2018, 05:29:04 PM »

Go for it! What could possibly happen?
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WZ8J
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« Reply #109 on: January 27, 2018, 05:31:06 PM »

Go for it! What could possibly happen?

tick, tick, tick....
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WZ8J
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« Reply #110 on: January 27, 2018, 05:33:07 PM »

Think I'll just parallel them with the existing caps, just in case...plus its easier. It'll give 30 UF but that shouldn't hurt.
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N1BCG
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« Reply #111 on: January 27, 2018, 05:50:31 PM »

Real Valiant owners keep fire extinguishers nearby so it almost doesn't matter what happens.
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WZ8J
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« Reply #112 on: January 27, 2018, 06:08:57 PM »

okay, no impact from that experiment. Hum is still there.
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N1BCG
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« Reply #113 on: January 27, 2018, 08:32:17 PM »

The only other power supply operating in standby is the bias supply. Try putting the caps there. How loud is the hum?
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WA1HZK
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« Reply #114 on: February 19, 2018, 06:40:10 PM »

Just tossing this out.
Bad pots, common problem but it sounds like yours are working.
Screen Bypass Caps shorting around the driver. 6AQ5 or 5763 I think. That drove me nuts on one way back.
Keith Clark
Wa1hzk
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