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Viking Valiant - No grid current




 
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Author Topic: Viking Valiant - No grid current  (Read 3716 times)
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N1BCG
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« Reply #75 on: November 23, 2017, 09:53:26 AM »

It's alive!

L43 is the choke in the choke input HV power supply. It might make a buzzing sound at higher plate current levels, but it shouldn't be affected by band. Smaller dips at higher loading settings (technically lower loading capacitance) happen when you tune to harmonics -- not desireable. The largest dip, and correct dip, is the one you see using the most loading (knob to the left, greatest capacitance). Once found, the loading is gradually reduced until the dip only goes down to the proper plate current when plate tuning is adjusted.

The loading changes could be due to more failed loading caps, particularly if the rig got a 180 Volt pulse at the mic jack. 450mA? Yikes. It's best to avoid 400mA at any time.

Try perfecting the 40M tuning and start looking around for new loading caps...

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WZ8J
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« Reply #76 on: November 23, 2017, 10:09:28 AM »

Okay,
Pretty much back to where I was before the bozo no-no event.
I readjusted the bias on the final and the clamper and now back to normal tune up and power out is a little over 125 watts on 40 & 80m.  Smiley
Still here the L-43 buzz a little on key down. Is this more or less normal?
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N1BCG
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« Reply #77 on: November 23, 2017, 10:21:26 AM »

Is it L-43 or the PTT relay under the chassis? In either case, it's not a concern. Now, about that mic plug... You can still use that mic, or any other, as long as the connections are correct. One idea is to fabricate a "Y" splitter with two separate leads with useful jacks on the ends. These would be wired to a three conductor plug to plug into the rig.

Your mic(s) would plug into the audio jack and a PTT switch into the other. Voltage measurement on the leads will quickly reveal which is for transmit (-180V) and which is for audio. BTW, a low to high audio matching transformer greatly improves performance when using low impedance (600 Ohm) microphones.

An important note: It's better for the "tip" lead to be used for keying. In this case, it's the last connection made as the plug is inserted and it eliminates the chance of keying voltage ending up in the mic lead. If this isn't the case, I highly recommend never plugging in or unplugging the connector with the power on if it's wired with audio on the "tip".
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WZ8J
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« Reply #78 on: November 23, 2017, 10:49:56 AM »

Hey Clark - again appreciate the comforting words. I feel like a passenger on a jet having to take controls when the pilots pass out from too much booze. I am being talked down from the tower. "Steady now, ease the stick gently forward.."
So I found in my daughters guitar things an adapter with a stereo end plug. I was thinking about plugging in the mono end of the mic cord into that and the stereo end into the mic jack on the rig, but I don't want any chance of a repeat of the last experiment.
Alternatively, could I just disconnect the wire to the SW8 that the previous owner connected and just flip the SW8 manually?
This seems safer than trying that jack with the 180V keying present.
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N1BCG
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« Reply #79 on: November 23, 2017, 11:20:44 AM »

Hopefully, discovery of this thread will save other Valiant owners from a heap of hassles. "We've done all the suffering for you" or somesuch grandiose claim.

Pilfering from your daughter, eh? I hope her guitar amp doesn't use 6146 tubes and she learns of the treasure trove of those in your Valiant!

The idea of running that kind of voltage in a microphone lead is unsettling as is holding a metal cased D-104 while connecting it to the transmitter.

Since we like talking to you more than talking about you, it might be wise to follow through on your idea of disconnecting the transmit lead and using the PTT switch on the chassis. Some ops added a low voltage relay and ran the relay voltage to the mic lead instead.

Seems like a good time to say Happy Thanksgiving!

 
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KA2DZT
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« Reply #80 on: November 23, 2017, 11:02:43 PM »

450 ma is a little much for three 6146s.  I think that's what is in a Valiant
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WZ8J
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« Reply #81 on: November 24, 2017, 09:05:54 AM »

Thanks for the input. I was just following the manual which says 450ma on cw and 330 ma on AM. I will take your advice and dial it back. I would like to preserve the finals, they are likely as old as the rig! Not sure when was the last time GE made 6146b's  Shocked
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N1BCG
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« Reply #82 on: November 24, 2017, 12:10:55 PM »

Supply voltages were a bit lower back when older gear was designed and the manufacturers established operating parameters based on that. With today's higher mains voltages and the substitution of solid state rectifiers, circuit voltages can be significantly higher than what is shown on schematics.

Because of this, some ops run their vintage gear on variacs or reduce operating currents to compensate.
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wa1sth
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« Reply #83 on: November 24, 2017, 05:38:02 PM »

Kudos to Clark for following through with this..What Amateur radio is about....
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WZ8J
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« Reply #84 on: November 25, 2017, 03:52:28 PM »

Okay Clark, not done yet he he.,

I am having difficulty deciphering the wiring diagram and how to properly connect the wires to the 80-MC2M jack.

The Valiant instructions are audio to pin 1 and switch to pin 2 - Uh that's sounds pretty simple.

The wiring diagram for the Electrovoice 719 is attached. I find it baffling.

The mike is equipped with a DPDT switch.

I have a black wire, red wire and a green wire and the braided shield coming out of the mike cable.






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N1BCG
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« Reply #85 on: November 25, 2017, 06:57:21 PM »

It looks as though it should work fine if you connect the shield and black wires to the mic connector case ( the strain relief spring ), the white wire to pin 1 ( mic ), and the red wire to pin 2 ( PTT ).

The Electrovoice 719 is a high impedance ceramic microphone so it could work well with the Valiant!
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N1BCG
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« Reply #86 on: November 26, 2017, 09:12:51 AM »

MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM

This post is dedicated to addressing the possible causes of HUMMM on the carrier.

Evaluation should be done with the transmitter feeding a dummy load and a receiver with no antenna or an outside antenna. The less obvious but important reason to not have the transmitter on an antenna is because radiated RF can mix with AC line currents and re-radiate with imposed hum. "Carrier-current hum" is a popular term.

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).

Setting the Mode switch to CW and keying will energize the high voltage power supply and generate full output. If hum is now heard then it could be failure of either or both of the high voltage filter caps (C91, C92), the HV choke (L43), or failure of either or both of the bias supply filter caps (C93A, C93B).

If it's C91/C92 then the HVB+ will increase a bit with working caps.

L43 can be tested by measuring the *A.C.* voltage drop across the terminals since it's there to present a high impedance to alternating current.

If either C93A or C93B is bad, the bias supply will actually modulate the finals with hum. As with the other caps, putting in working caps will cause a jump in supply voltage.

To eliminate the possibility of hum coming from the modulator, be sure that the modulator screen voltage is "0" when the transmitter is keyed in CW. The Mode switch grounds the screen circuit (tube socket pin 3) and shorts out the secondary of the modulation transformer.
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WZ8J
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« Reply #87 on: November 26, 2017, 09:09:25 PM »

To all of those who thought our saga was drawing to a close with the Valiant riding off into the AM airwaves...think again.
Testing on dummy load on AM and heard a ssst and a bit of a flash and now she blows fuses immediately on switching to HV.
Nosing around, I pulled the 5V4. It doesn't look good. The plates seem to have a warp in them when viewed from the side. I thought this was the tube that produced the brief flash before things got quiet.
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N1BCG
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« Reply #88 on: November 26, 2017, 10:16:19 PM »

Nosing around, I pulled the 5V4. It doesn't look good. The plates seem to have a warp in them when viewed from the side. I thought this was the tube that produced the brief flash before things got quiet.

Pictures, please.

Yep, if the 5V4 develops a short then that could easily explain the blown caps. As for blowing fuses when the HV is switched on, it sounds like it's time to use that 150W bulb in series with the power cord and measuring the HVB+ (which should be more than zero but less than 600 in this "safety configuration".
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WZ8J
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« Reply #89 on: November 27, 2017, 07:12:38 AM »

Thanks Clark,
I will pick up a 150 watt bulb on my travels today. Don't have one in the house. The 100 watt I have isn't high enough power to be helpful.


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N1BCG
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« Reply #90 on: November 27, 2017, 09:20:20 AM »

I will pick up a 150 watt bulb on my travels today.

...and a 5V4. The cathode and plate aren't that far apart, so any malformation could easily cause a flashover or short.
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WZ8J
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« Reply #91 on: November 29, 2017, 03:19:36 PM »

Got a 150 watt incandescent bulb from Home Depot so my current limiter is now good to go. The tube filaments light up and I show some current on the meter in both buffer and oscillator settings. No grid current. When I switch to HV, no red light.
I would like to test the L-43 HV choke for shorts. Any suggestions on how to go about that?
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KB2WIG
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« Reply #92 on: November 29, 2017, 03:28:38 PM »



Carefull place meter accross the choke.  Short=0 volts.

Carefully.

Carefully.

Klc
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What? Me worry?
N1BCG
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« Reply #93 on: November 29, 2017, 05:03:27 PM »

I'm going to assume that the 5V4 low voltage rectifier was replaced, which is why you're getting any meter readings. As for grid drive indications, you may need to turn up the drive control since the transmitter is running at reduced voltages. That could also prevent the PTT relay from closing and activating the HVB+.

You could also try using an insulated tool to manually press down on the relay wiper to close the HV circuit. It's a small relay on the underside of the chassis on the left side. Be ready to measure the HVB+ at the caps in the power supply. It will be a bit low due to the bulb, but at least it shouldn't be zero.

How bright is the bulb when the variac is at max?
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WZ8J
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« Reply #94 on: December 01, 2017, 07:24:37 AM »

The Valiant lives!!!
On air last night with Clark, N1BCG who devoted hours and hours on line and on phone with me to get this rig running. We found the buzzing was due to the modification a previous owner made by adding the phone style mic jack to the front panel.
Can't thank Clark enough for taking virtual "Elmer" to a whole new level. The learning was invaluable and probably worth all the hassle (for me at least).
I would also like to thank Tim, WB8UHZ who sent me a couple tubes and crystals when I first got "El Valiante" and also all those who posted on this site to help me along.
I hope that others will be helped by this thread as they undertake the restoration of these great old boat anchors.

73's until the next sparks fly  Grin

Kevin
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