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THE AM BULLETIN BOARD => Technical Forum => Topic started by: WZ8J on September 12, 2017, 01:56:11 PM



Title: Viking Valiant - No grid current
Post by: WZ8J on September 12, 2017, 01:56:11 PM
I've got a Viking Valiant - (later kit version) Can't get any grid current on the meter.
I have done checks on the meter and I think its okay. The meter will display to half scale on the oscillator position and quarter scale on the buffer position, but no deflection on grid, nor on plate position.
I can hear the signal in a receiver using either crystals or the VFO.
I can adjust the signal strength in the receiver by tuning the exciter, course and fine coupling and final tuning. Same behavior with a crystal and VFO on either 40M or 80M and on other bands using VFO.
Checked the drive pot and it is operating correctly.
Resoldered suspect looking cold solder joints on the mode and oscillator switches and other points under the chassis.
Checked to make sure the square aluminum cam actuated by the band switch shaft with the notches in the proper position for the band
I have substituted the 6CL6 (Crystal Osc. Buffer) and the 5763 (multiplier) with good tubes (thanks WB8UHZ!).
I subbed the finals for known good 6146B's
I replaced the Chernobyl resistor in the VFO with an 18K 10 Watt.
Recapped the electrolytics.
Someone added a phono jack on the front panel for a mic.
Some of the resistors appear to have been changed using modern components.

So can someone give me a roadmap on where to go next? Would love to get this old gal on the air. She looks very clean inside and out with very little dust and no corrosion.
I have schematics and the manual.

I have VOM's a VTVM and a scope. I know how to work safely around high voltage.
Any advice is welcome. I have not repaired much equipment but did repair a TS 520 and rebuilt an SB-220, so that is the limit of my experience.

Thanks folks!







Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 12, 2017, 08:04:35 PM
Try pulling out all three 6146 tubes and see if you get RF on the grid circuit. The concern is damaging these tubes with too much drive if the metering circuit is faulty. It's also possible that the driver tank circuit isn't tuning correctly although you mentioned the signal on a receiver which suggests it is functioning correctly.

Have you checked the RF bias setting? There should be approximately -70 volts on the grids of the 6146 tubes.

None of these tests require the transmitter to be keyed. Lots of stuff to try...


Title: Re: Viking Valiant - No grid current
Post by: N3GTE on September 12, 2017, 08:13:23 PM
Have a look at the metering switch. Make sure the contracts are clean and tight.

Terry N3GTE


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 12, 2017, 08:42:40 PM
Thanks Clark,
Looks like it's only about -50V on the grids.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 12, 2017, 08:48:57 PM
The RF bias pot (lower one on right side of chassis) should have enough range to give you -70 volts. If not, check the bias supply for proper negative voltages. That supply affects several things so it has to be functioning properly. Either a weak rectifier tube or bad filter caps can cause low bias voltage.

I also second Terry's suggestion. A great place to start.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 12, 2017, 09:12:32 PM
I adjusted the bias and now have -70V on the amp grids.
Still no effect on the grid current.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 12, 2017, 09:15:23 PM
Those tabs on the meter switch contacts look a bit fragile. I am lothe to break them. I sprayed em with some tuner cleaner.
Still no joy.  :P


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 12, 2017, 09:29:10 PM
Check the continuity from the meter to the grid circuit. When set to "Grid" each lead of the meter is connected to R57 (5.1 Ohms). You could also connect a VOM to that resistor, and when set to a low voltage range, see if you get a reading.

Btw, switching the Oscillator switch to Zero turns on the VFO and all stages up to the 6146 grid circuit for testing safely.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 13, 2017, 07:30:44 AM
Okay Clark,
I checked and have continuity from R57 to the meter. The meter on the rig deflects when the VOM is connected across that resistor.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 13, 2017, 10:09:15 AM
The meter on the rig deflects when the VOM is connected across that resistor.

Hmm.

I made an "RF diode" for testing circuits like this. It's basically a diode detector with a 0.01 cap to filter out everything but the resulting D.C. Measuring the RF voltage at the grid terminal on one of the 6146 sockets should show a pretty substantial voltage that can be peaked with the "Exciter" control.

Analog VOMs set to A.C. can usually do this. The other lead doesn't need to be connected. This won't yield an accurate measurement of P-to-P voltage but it will show relative signal.

The main concern about no grid current is that, if it's true, then the 6146s will conduct way too much and could be damaged. The plate current meter would pin. If that's not happening then the clamper tube is doing its job by sensing the lack of drive and pulling the screen supply down to a safe level of plate dissipation.

Try the VOM test. If the RF level isn't substantial then you might have a bad coupling caps (C97, C98). These are two red mica caps in parallel. The RF level should be the same on both sides of these caps.

Are you sure the 5763 tube is good? Ah! And one more thing... check that the drive control is actually providing 0 - 300V on the center (wiper) lug (be careful!). This is a wirewound pot that often wears out.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 03:37:27 PM
Okay Clark,
Again, thanks for the direction. I did verify that the DRIVE pot can be adjusted from 0 to 300V.
I tried the analog VOM on AC at the mica coupling caps. Very low reading on the grid side of the amp a slightly higher reading on the coil side. Changing the EXCITER level did not have a noticeable effect on the RF level measured with the VOM.
So, if these caps need replacing, can I substitute a single 50 mfd for the two 25 mfd caps in parallel? Could I use an electrolytic?

Finally - I have no way to check the 5763, I did get a replacement and swapped it, but no impact on the grid drive.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 04:09:01 PM
Changing the EXCITER level did not have a noticeable effect on the RF level measured with the VOM.

There's the first clue. The exciter control is actually the tuning control for the 5763 plate / 6146 grid circuit so you should see the voltage peak at resonance. The "Drive" control varies the output of the 5763. Where was that set? Most of the time they're around the 10-11 o'clock area.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 04:42:45 PM
I had the drive at about 3-5 (9-11 o'clock). But adjusting it does not move the meter noticeably.

Also the mica caps are marked 25 MMF not MF as I mentioned in the previous post,
so I guess we are talking pico farads rather than micro farads so never mind about the electrolytic substitution question.  ::)


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 05:00:42 PM
Try this on 160, 40, 10 with the VFO and using a crystal (be sure it's in the right pair of connections on the 8 pin socket and that the Oscillator switch is set correctly. This will allow you to see if any of the circuit combinations produce drive.

Also be sure that the Mode switch is set to "AM".

The meter switch will show the cathode current for the 5763 when set to "Buff" and reads "13" (bottom scale X2) on my Valiant. The Drive control will have a large effect on that reading. For comparison, my Osc reading is "24" (bottom scale X2).


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 08:06:05 PM
Okay,
Let's see how many pages we can extend this thread to!

So I set the mode switch to AM
I only have two Crystals one for 40 and 1 for 75 but I put one in the socket anyway. Fortunately a previous owner dabbed some green ink on the correct pins.
OSC to "zero"
and here are the meter readings (bottom scale X2) for the bands:
160 Buffer 4, Oscillator 20
80  Buffer 6, Oscillator 20
40 Buffer 8, Oscillator 15
20 Buffer 6, Oscillator 15
10 Buffer 5, Oscillator 16

So inspector who do you think is the likely culprit? Are we getting closer to solving the mystery?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 08:22:49 PM
I swear, Valiants are responsible for most of my gray hair...

Does the Drive control have any affect on the Buffer readings?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 08:25:28 PM
Oh yes, it adjusts it quite a lot in fact.
I should have mentioned that all of the buffer and oscillator readings were done with the drive all the way down.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 08:35:38 PM
OK, well you're going to need some amount of drive so what you had around 9-11 o'clock is reasonable for testing.

With that set and the VOM on AC and connected to one of those mica cap leads, adjusting the Exciter (tuning) knob should result in a peak in VOM reading.

If not, then I suspect a bad connection on the wafer switch which selects the proper tap on the driver tank coil (it's the vertical inductor behind the VFO cabinet).


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 08:59:04 PM
Do you measure high voltage on the driver tuning cap (C7)? And, because I have to ask, is the shaft slipping or does the knob turn the cap fully?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 09:10:01 PM
Yes of course the shaft slips. I seem to have to really tighten the set screws, but if I snug em up good and only trn the knob clockwise, it doesn't slip.
I haven't tried to measure anything on that air variable cap. What voltage should I find there?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 09:16:35 PM
By slipping I meant that the knob is actually turning the cap. It just seems like you're not able to get an RF peak on the meter which suggests that the tank circuit isn't getting tuned.

That cap will have 300 volts on it, full 5763 plate E!

We're basically testing the tank circuit connections...


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 09:17:47 PM
Okay Clark,
I show 356 volts across C7 in AM on "ZERO" position and 377 volts on AM on "VFO" position.

I noticed that issue too, that cap is kinda stiff to turn, but yes, it is opening and meshing the plates.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 09:24:14 PM
That's about right for voltage. I should have mentioned that the Oscillator switch should be set to "Zero" in order to get proper RF at the mica caps. 


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on September 18, 2017, 10:03:56 PM
Yes thanks, I did that in fact tried all the positions for the RF reading at the mica caps but no change. I wonder if I should try it with the oscilloscope?
You think the micas might be the suspects? - I think I saw them on the freeway in a white bronco.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on September 18, 2017, 10:13:41 PM
Does the "Buff" reading change on the Valiant meter as you tune the Exciter control? It's just as if the driver tank isn't getting to resonance.

Are the wafer switch contacts clean for the bandswitch switch under the aluminum shield?  It should have several wires of different colors connected to it from the driver tank coil.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.  :-\


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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...


Title: Re: Viking Valiant - No grid current
Post by: DMOD 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.  :-\

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


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: KB2WIG on September 25, 2017, 03:25:03 PM


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



klc


Title: Re: Viking Valiant - No grid current
Post by: WBear2GCR 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.

                  _-_-


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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... ???

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.


Title: Re: Viking Valiant - No grid current
Post by: WD5JKO 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
Wd5JKO


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: DMOD 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



Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 04, 2017, 10:58:41 AM
Started a new job with my company and been traveling extensively so haven't worked on the Val-Ain't lately except that I did pick up some SS HV plug in rectifiers to replace the 3B28's of unknown status. I also installed new 82uf 450V electrolytics to replace the old ones that someone had installed on the incorrect pins of the HV rectifier tubes.

I found the construction manual for the Valiant kit on line. This is a helpful guide.
Did the suggested resistance checks and got the following results:

PIN 3 of XV20 Resistance should be 10.8K, got 56.5K
PIN 1 of XV12 Resistance should be 250K, got 314K
PIN 6 of XV12 Resistance should be 60K, got 109K
PIN 1 of XV14 Resistance should be 60K, got 67K  :)
PIN 2 of XV18 Resistance should be 20K, got 40K
PIN 5 of XV21 Resistance should be 12.2K, got 9.7K

Seems okay on LV. No attempts at HV at this stage.
Want to be confident before I throw that switch.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 05, 2017, 11:34:16 AM
Managed to tune up the Valiant last night  :D
Low output. Only getting about 45 watts out into a dummy load on CW. Probably have soft tubes.
Can only get about 225ma plate current.
Haven't checked the audio stages, don't have a microphone plug for the two prong jack. Will either need to replace that or find a male plug on ebay.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 06, 2017, 11:44:53 AM
If you're getting sufficient grid current (7.5mA) and the final bias voltage is correct (-70vdc) then it's likely you have one or more slacking 6146 RF tubes. Also be sure they're all lighting. I've heard a case where one of the tubes' heater wasn't lit due to dirty pin connections. One reason or another, someone's not putting out.

Another possibility is one or more shorted loading caps. This would limit how little loading can be set and artificially cause too great a dip. Check that confounded turnstile cap and each of the micas in series between the AUX loading switch and the chassis. Conversely, plate current that can't be dipped low enough is indicative of open loading caps.

A clever way to check the output tuning network is with an antenna analyzer such as what MFJ makes. With the transmitter unplugged and all caps discharged, clip a 2200 Ohm (or close) resistor between the plate cap of one of the RF tubes and the chassis. Connect the analyzer to the antenna connector via a short coax jumper and set it to the center of a band that the transmitter can operate on. With the analyzer set to display resistance and reactance, tune the transmitter as though it were on. You should be able to find a nice 50Z +/- 0j match. If not, there's something rotten in the output circuit. Try this on each band, particularly 160 as that band requires all of the loading caps to be working.

** The output tuning and loading controls are merely an impedance matching circuit from about 2000 Ohms (the three tubes) to 50 Ohms (the antenna). It works both ways!


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 07, 2017, 09:09:10 AM
This was an "aha" for me Clark. Thanks for that last post:
Another possibility is one or more shorted loading caps. This would limit how little loading can be set and artificially cause too great a dip.
I noticed this artificial deep dip and saw that the power on the Bird watt meter went down, so I knew it was not a resonant point.
Also - since I last posted I subbed in a known good 6124B in the final and now showing 178 or so watts out on CW!
I achieved this by tuning for max output power on the watt meter not by the dip in the plate current.
I will have to check those loading caps for shorts as you directed.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 07, 2017, 09:30:21 AM
--- N I C E ! ---  aka  _.   ..   -.-.   .   !  since you're using the CW mode.

That deep dip shows tank circuit resonance, but little coupling with the output, so a low output power indication is expected. That's where the loading caps come in. The value is gradually reduced to the point where maximum power is transferred to a 50Z load.

Of course, maximum power is also limited by the tube ratings. I use 300mA of plate current for AM and CW. While it's a bit lower than the manual specifies, it's easy to see that the pointer is on "300" and it's gentler on the modulator and finals. The transmitter was designed in the 1950s when line voltages were lower, so lowering the current helps compensate for the higher resulting plate voltages.

You can use a wattmeter for tuning, but be mindful that the plate current doesn't soar. The traditional method of tuning is to lower the drive level somewhat to prevent excessive plate current while dipping and loading (never adjust the AUX switch while keyed up). The drive level is then gradually increased to a max of 7.5 mA of grid current and the dip at the proper plate current reading set with the loading controls.

Sounds like a lot, but ops back then had a pipe in their mouth and a wife to bring them a Rhinegold or somesuch beverage to aid on the process.


Title: Re: Viking Valiant - No grid current
Post by: w1vtp on November 07, 2017, 10:08:04 AM
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.

My series bulb tester / current limiter includes a variac. My first AL-82 power transformer had an internal zorch. I could tell as I brought up the variac when the zorch occurred the bulb would flash brightly but no blown fuses / breaker panel trips.

Should work with the Valiant. Maybe use an even higher wattage bulb.

a


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 07, 2017, 06:46:57 PM
I'm not believing my plate current readings. They appear to be way low, especially since I am getting close to 200W out on the Bird watt meter. :o
What is a safe way to check the plate current near the meter with VOM? I don't want to damage the meter on the rig, but I need to see if the meter is reading accurately.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 08, 2017, 05:41:52 PM
Begin testing at R58. It's 0.202 Ohms made from a short length of resistance wire. That value isn't easy to measure, but you could measure the voltage across the meter contacts when it's set to "Plate". With that setting, the meter is indicating the voltage drop across R58. Incidentally, I believe the panel meter reads 5mA FS.

A lower than expected plate current reading could be caused by dirty meter switch contacts. Does rocking the switch cause the meter to read differently?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 17, 2017, 07:34:27 AM
Okay,
I knew the output power was suspect. I changed the short coax jumper between my watt meter and the dummy load and found that I had a defective coax. The power readings were distorted because of the reflected power.

With a good jumper in place I am getting 50 watts out on 20M and about 20 watts on 80M.

I tried subbing in some new final tubes I had from my TS520. No real change in output. I think this means one of two things:
either I still have a bad tube in the trio of 6146's amongst my selection, or there is something else limiting the plate current.

Other anomalies:

cannot achieve normal levels of plate current during tune up. The highest plate current reached is tuning up on 160M and getting 250ma but only about 12 watts output.

best output is on 20M at about 55 watts but only at about 120ma IP.

Get very low meter readings on buffer and oscillator meter positions when oscillator switch is on VFO.
 
Get more normal readings on both buffer and oscillator when oscillator switch is set on "zero"

I can only get Ig when I advance the drive pot a little, but I think that is pretty normal.

Rechecked the bias voltage and it is now at 72v. Not sure why this doesn't stay put at 70V or if it is that critical.

I am wondering if the buffer or oscillator tubes are weak, or if there is some component in those circuits not operating correctly.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 17, 2017, 10:07:12 AM
I use 160M and 40M for tests since there's no frequency multiplication on those bands and the lower frequencies put more of the output network to the test (requiring more caps in the circuit). From your tests, it looks like you're getting about 8% efficiency on 160M and 76% on 20M. Are you getting 7.5mA of grid current on the finals without setting the drive control past 12 o'clock?

This sounds like low 6146 screen voltage / improperly set 6AQ5 clamper circuit. The clamper circuit is a protective system that prevents destructive 6146 current with drive loss. When active, the 6AQ5 tube conducts and drags down the 6146 screen voltage. R13 is used to adjust the threshold (check the manual for details).

The efficiency discrepancy may be caused by faulty caps in the tuning circuit and you're actually tuning the output to a harmonic of the intended frequency.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 17, 2017, 01:15:16 PM
Again thanks for all the helpful instruction I hope to soon graduate with my degree from Valiante University  8)

I used my MFJ antenna analyzer to check the tank circuits per your recommendation.
I found that I could not get a decent match on 160M. I did on 80M and 20M. Looks like I need to check those loading caps.

I will also try adjusting the clamper again. Last time I did this I don't recall getting much adjustment.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 17, 2017, 01:29:37 PM
I will also try adjusting the clamper again. Last time I did this I don't recall getting much adjustment.

That's a clue. Under the setup conditions, the plate current will slam if R13 is adjusted too far in one direction, and it will never be able to rise sufficiently under normal operating conditions if adjusted too far in the other.

The clamper threshold, R13, is set much like a squelch control. You should definitely see the effect during the adjustment process!


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 17, 2017, 06:29:55 PM
Well that was it. I didn't realize the pot for the clamper could be turned more than 360 degrees! Doh!
I got it adjusted to 10 ma and now have plenty of plate current.
Moved on to the operational checks in the manual after clamper is set but did not pass the first check:
Oscillator current should read about 24Ma - I've got 28 ma - close
Buff should read about 6 ma - I'm showing 4 ma
Switch meter to grid and tune exciter to max current with DRIVE in position 3
Adjust grid drive to 3 ma (bottom scale)
Turn meter to PLATE and throw SW8 to "MAN" and tune final for Minimum current - Should get 80ma, I GET 390ma


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 17, 2017, 06:58:37 PM
Well, grid current should be 7.5mA, but if it's low, the plate current should be low also. Double check the clamped setting. It can be tricky to get just right.

R13 turns completely around? It might be damaged.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 17, 2017, 07:30:50 PM
Yep the Ig is fine 7.5ma
It's the Ip that's high.
I'll check the clamper adjustment again. It calls for 10ma which is a very fine reading on that top scale for plate current.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 17, 2017, 07:34:53 PM
Also try a higher band. You may not have enough loading capacitance to get a sufficient dip.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 17, 2017, 08:02:44 PM
Okay,
Looks like it tunes up good to about 125 watts out on CW on 40M!

I'm starting to think the C47 I think multi stage cap is a little knackered.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 17, 2017, 08:20:05 PM
Ah, nice!! Yep, that "turnstile cap" is notorious for failing. You can replace it with 300, 600, 900, and 1200pF caps (I think). Check my memory...

I expect to hear you soon on 40M!


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 09:13:14 AM
I was able to load up the finals to the proper plate current on cw on 20m, 40m, and 80m. Cannot get proper loading on 160m which I suspect is a loading cap issue.
I was able to adjust the mod bias to -55, but this was a rather touchy adjustment and it has a tendancy to easily bounce around. Wonder if it wasn't fully warmed up or if there is a component in the circuit breaking down a little,

Either way should be able to get this rig on the air soon. 8) 8) 8)


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 10:45:37 AM
Spoke too soon...
Disaster strikes. I had a studio mic with a phono jack which I plugged into the front mic jack some previous owner installed and pow- fireworks and some smoke. I fear I may have shorted the mod transformer  :'(


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 12:11:45 PM
Typical Valiant, unfortunately.

What do you think happened? Did the fireworks happen when you spoke into the mic or when you plugged in the mic?

It's a good time for that series 150W bulb in the power cord...


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 01:18:08 PM
It happened when I plugged it in. SW8 still on PTT.
I have a variac, won't that accomplish the same thing as the 150W bulb?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 01:33:06 PM
Trying to piece this together... so the transmitter was set for "AM", on standby, and just needed to be keyed? Then the mic was plugged in and BANG!  Right?

Is that added jack definitely for a microphone and does it include a contact for keying? If so, what might have happened is the -180 Volts used for keying got into the audio input circuit and that would have sent a thunderous pulse through the modulator. Is the studio mic wired with a PTT circuit? Usually those mics are balanced 600 Ohms where two leads are for audio and the third is grounded. I'd be surprised if it were wired for PTT if it had a 1/4" plug.

Where did the smoke rise from?  I'd trace the leads from that added jack to confirm its purpose. Variacs are very handy, especially if they have a current meter.


Title: Re: Viking Valiant - No grid current
Post by: KA2DZT on November 22, 2017, 01:37:48 PM
It happened when I plugged it in. SW8 still on PTT.
I have a variac, won't that accomplish the same thing as the 150W bulb?

Not exactly,  the light bulb prevents a heavy short from damaging the xfmrs and other parts.  A Variac doesn't do anything to prevent damage from shorts.

Fred


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 02:35:43 PM
I think you're on the right track Clark. The studio mic has no ptt.
The jack is wired to the audio pot and to the hot side of SW-8
The smoke looks like it came from arcing at C98 (Electrolytic cap on the 5V4 to ground. C98 came unsoldered from the ground lug.
The leads from T-3 mod transformer are all connected to a terminal strip.
I measured resistance from each lead to each of the others and found them all shorted.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 02:49:16 PM
Don't necessarily be concerned about the mod xfrmr resistances. Those windings have relatively low D.C. Resistances. So far, it just sounds like a cap failure.

Got replacements for both? A shorted 5V4 could have done that.

Also, only use a stereo (3 conductor) plug and keep the tip and ring leads well separated. One is for low voltage audio, the other has -180 volts on it for keying when connected to ground/shield.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 03:35:42 PM
You mean all might not be lost?
I do have replacements for the C98 dual cap.
I'm going to check the pin out for the 5V4 and check for shorted tube with my VOM


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 03:48:49 PM
You might be fine. Put your voltmeter on either + lead of that cap and to the chassis to monitor LVB+ as you bring up the Valiant on the variac.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 05:48:17 PM
what should the LVb+ be 300V?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 06:21:29 PM
300 Volts approximately. Mine shows a bit more because line voltage is higher now than in the 1950s. Anything from 300-340 should be ok.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 06:34:32 PM
with the caps replaced, all seems well bringing the voltage up.
I have 125V AC line voltage here. If I turn the variac up all the way, it goes to 367 volts. Is this kinda high?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 07:49:44 PM
That's a bit high but not critically. You could always use the variac to re-create 1957 voltage :-)


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 22, 2017, 09:04:14 PM
Ha! yeah. Well what do you think the next step should be. I am a little HV shy but everything on LV is looking normal.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on November 22, 2017, 10:20:26 PM
I think the whole AMfone community is on pins and needles over this. Time to take a deep breath and go for it (but keep that mic unplugged). The failure was in the low voltage supply and that's been fixed.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on November 23, 2017, 09:19:55 AM
Okay,
I tuned it up on 80m, 40 and 20m.
No smoke or sparks - yeah!
The rig is tuning differently now. Here are my observations:
On 80m, L43 buzzes noticeably on key down
Power is lower than before got about 90 watts out when before I was getting 125
Get very small dips in plate current at advanced loading settings
Loads better on 40m but seems to take more advanced loading to get to full (450ma plate current). Power about 100 watts now.
I am guessing the stress of the "event" stressed out components in the loading circuit that were already weak?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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...



Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.  :)
Still here the L-43 buzz a little on key down. Is this more or less normal?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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".


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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!

 


Title: Re: Viking Valiant - No grid current
Post by: KA2DZT 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


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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  :o


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: wa1sth on November 24, 2017, 05:38:02 PM
Kudos to Clark for following through with this..What Amateur radio is about....


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.






Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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!


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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".


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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?


Title: Re: Viking Valiant - No grid current
Post by: KB2WIG on November 29, 2017, 03:28:38 PM


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

Carefully.

Carefully.

Klc


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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  ;D

Kevin


Title: Re: Viking Valiant - No grid current
Post by: K3FEF on December 16, 2017, 06:59:36 PM
Just chiming in to follow. :-)  Spoke with WZ8J on the air tonight and we confirmed (from schematic) that the R61 pot is a 2W and not 25.   So hopefully next time I hear Kevin it will be on the Valiant. :-)  Because that 25W 5k pot sure would be BIG. LOL  Thanks again for the QSO Kevin.  73!!


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on December 27, 2017, 11:42:46 AM
Looks like the some of the loading caps have now given up. I can no longer get the plate current to dip below 450ma to be able to operate on 75M phone. I can still load up fine on 40 & 20.
Not sure if it is the turnstile cap that is bad or the padding caps for 80M. Some of the transmitting and door knob caps are pricey - what is a good approach to replacing these? Anyone know of a good source?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on December 27, 2017, 03:18:33 PM
Update:
Stumbled across this bit of info from Wireless Girl: http://www.wirelessgirl.net/Projects/AMTransmitters/LoadingCapacitorRepair.html
So I've ordered some MLCC caps.



Title: Re: Viking Valiant - No grid current
Post by: N1BCG on December 27, 2017, 06:44:44 PM
It's easy to check transmitter output tuning circuits if you have an antenna analyzer or an impedance bridge and know the plate resistance (which is usually easy to calculate: Normal Plate Volts / Plate Amps = Plate circuit Ohms).

With the transmitter unplugged, connect the analyzer to the antenna connector, a non-reactive (carbon) resistor between the RF PA plate circuit and the chassis, and set the bands on the transmitter and analyzer to the same setting. For Valiants, an 1800 or 2200 Ohm, 1/4 Watt resistor works fine (600 Volts/0.3 Amps). An exact value isn't critical.

While watching the impedance and reactance, adjust the transmitter's tuning and loading controls to obtain a 50Z +/- 0j readings, if possible, on each band. Loading capacitor issues will be most noticeable on lower frequencies such as on 160M.

This method of "back feeding" the output tuning circuit permits a safe way to troubleshoot tuning and loading problems by using low levels of RF.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on December 28, 2017, 09:50:02 AM
Following this procedure with a 2K ohm resistor from plate cap to ground on the finals using MFJ antenna analyzer yields 1.2:1 SWR at 36 ohms - best possible on 3880 khz


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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.  



Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: KD6VXI on December 29, 2017, 06:49:07 PM
That could completely be within the tolerance of an Mfj device.

--Shane
KD6VXI


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.
 


Title: Re: Viking Valiant - No grid current
Post by: WD8KDG 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


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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?


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on January 27, 2018, 05:29:04 PM
Go for it! What could possibly happen?


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on January 27, 2018, 05:31:06 PM
Go for it! What could possibly happen?

tick, tick, tick....


Title: Re: Viking Valiant - No grid current
Post by: WZ8J 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.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG on January 27, 2018, 05:50:31 PM
Real Valiant owners keep fire extinguishers nearby so it almost doesn't matter what happens.


Title: Re: Viking Valiant - No grid current
Post by: WZ8J on January 27, 2018, 06:08:57 PM
okay, no impact from that experiment. Hum is still there.


Title: Re: Viking Valiant - No grid current
Post by: N1BCG 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?


Title: Re: Viking Valiant - No grid current
Post by: WA1HZK 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
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands