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Valiant Restoration K3MSB




 
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Author Topic: Valiant Restoration K3MSB  (Read 8562 times)
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k3msb
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« Reply #50 on: January 29, 2018, 09:38:00 AM »

Hi Fred (KA2DZT)

I think we're talking about two different things.    I first put my external meter between the output end of L43 and the junction of C91/R17.   This reading was a bit high and someone pointed out that this would include the bleeder current etc.   Clark then suggested I move the external meter to be between J8-3 and J8-5 so as to get rid of the bleeder component.    This meter consistently reads the same and seems to be correct.     I think this is equivalent to what you suggest.

Clark posted "What happens if you put your known good meter in series with the Valiant meter? They should read the same current with 5mA full scale"    I misinterpreted this to mean the Johnson meter reading would not change if I had it set to 450 mA (full scale) before inserting the meter.    Thinking about this,  although the new meter (or DVM etc) is now in series with the Johnson meter,  BOTH are across the 0.202 ohm shunt.   So, the lower readings I though were incorrect were probably correct;    I need to ensure that whatever the Johnson meter is reading matches what the inserted device is reading --  which will not be the same as the standalone Johnson meter.

So, I have one data point that shows 100 mA across the meter full scale with my DVM measuring 5 mA which is correct;  how the devil I configured that I'm not sure -- I have a lot of wires hanging out there.....
       
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73 Mark K3MSB
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« Reply #51 on: January 29, 2018, 01:07:05 PM »

Another thing to try is to set your Fluke to volts and measure the voltage drop across the Valiant meter. The benefit is that it won't affect the meter reading. Once you have a cross-reference between it's current reading and your voltage reading, you'll be able to see if anything changes like it's done during the last test.
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k3msb
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« Reply #52 on: January 29, 2018, 07:50:29 PM »

With no DVMs attached,  I set the Ip to 500 mA (FS) and noted the external meter indicated 335 mA.

I put the DVM #1 in series with the Johnson meter, and DVM #2 across the meter.

This means DVM #1 and the Johnson meter are both across the 0.2 ohm shunt.

DVM #1 indicated 3.28 mA
DVM #2 indicated 64.4 mV.
Johnson Meter showed 335 mA (Ip scale).

Johnson meter is 335/500 mA = 0.67% deflection.

Current should be 0.67 * 5mA = 3.25 mA this is what  DVM #1 shows.

Voltage should be 0.67 * 100 mA = 67 mA this is what DVM #2 shows.

Granted the current and voltage is wrong as I have a DVM and the Johnson meter across the 0.2 ohm shunt,    but they are correct for a 335 mA Johnson meter indication.

The external Meter shows about 335 mA Ip, which in this case does not correlate to the 335 mA Johnson meter reading. The external meter is hooked between J8-3 and J8-5

Im starting to conclude the meter itself is OK.   Comments?
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73 Mark K3MSB
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« Reply #53 on: January 29, 2018, 08:31:54 PM »

So the question is if the meter readings are accurate for all the meter switch settings. If so, then you just need to find a stable resistance to put in parallel with the shunts to make the meter readings accurate for the parameters that are off.
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k3msb
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« Reply #54 on: January 29, 2018, 09:13:11 PM »

From one of my previous posts:

I decided to put a 0.9 ohm resistor in parallel with the 0.2 ohm Ip shunt.   This dropped the Johnson current meter reading by about 30 mA.      I then put a 0.2 ohm resistor in parallel with the 0.2 ohm Ip shunt and this dropped the Johnson current reading by 50 mA.    Putting in a lower parallel resistance did nothing more;  I even tried using resistance wire with the length such that it was almost negligible.  There must be something else in the circuit that has a low enough resistance that is taking over as the lowest resistance;  not sure what.    In any event,  using a lower value shunt does not look to be the answer.

That last part bothers me.

I've removed the modulators so the 0.404 ohm shunt shouldn't enter into the issue.

There's nothing else in that circuit.    Maybe remove C52 off the Clamp tube?   But if that was leaky,  it in parallel with the 0.202 shunt would cause the effective shunt to be smaller and the meter reading to be less, not more.

 Huh Huh Huh
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73 Mark K3MSB
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« Reply #55 on: January 29, 2018, 09:24:37 PM »

At this point, I say forget the Valiant. We need to find some dingy dive-bar with a dirt cheap beer special, scorching hot wings and a huge plate of nachos and exchange Valiant war stories. Actually, I've heard all of yours from the beginning so I'll do most of the talking, lol. You can pick up the first round...

Time for those other Valiant geniuses to chime in..
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KA2DZT
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« Reply #56 on: January 29, 2018, 10:36:50 PM »

I would recommend that you recheck the ground connection on the 0.202 shunt.  The slightest amount of resistance on the ground connection will cause the PA plate current to read high.  That's why when you keep reducing the shunt resistor with parallel shunts it stops making any reduction in the reading....

Have to take another look at the schematic,  I'll be back

Ok, I looked over the metering switch.  Again, make sure the PA current shunt is grounded.  To eliminate any possible grounding problems,  run a ground wire from the PA shunt ground lug to the ground lug for the ground on the meter switch.

Make sure there are no cold solder connections.  Resolder the ground connections with fresh solder.

Once you have a 100% good connection between the PA shunt resistor itself and the metering switch you should get correct readings.  Slightly poor connections on the meter switch will cause the meter to read low not high.  But, the only thing that will cause the PA current to read high is a poor ground connection at the PA shunt or a shunt resistor that has increased in value.

I also looked at the octal plug connections.  Placing a test current meter between J8-3 and J8-5 should read the same PA plate current that is passing through the shunt.  That meter will be in the B+ voltage line so you have to be careful.

Fred
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k3msb
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« Reply #57 on: January 30, 2018, 08:25:48 AM »

Good Morning Fred

I would recommend that you recheck the ground connection on the 0.202 shunt.  The slightest amount of resistance on the ground connection will cause the PA plate current to read high.  That's why when you keep reducing the shunt resistor with parallel shunts it stops making any reduction in the reading....

The ground connection has already been completely redone.

Quote
Ok, I looked over the metering switch.  Again, make sure the PA current shunt is grounded.  To eliminate any possible grounding problems,  run a ground wire from the PA shunt ground lug to the ground lug for the ground on the meter switch.

I can try that.   I also thought about just moving the entire shunt atop the chassis near the meter switch.

Quote
Make sure there are no cold solder connections.  Resolder the ground connections with fresh solder.

As said, the ground connection has been rebuilt.   I'm pretty sure I checked for cold solder connections elsewhere,  but reflowing them won't hurt.

Quote
I also looked at the octal plug connections.  Placing a test current meter between J8-3 and J8-5 should read the same PA plate current that is passing through the shunt.  That meter will be in the B+ voltage line so you have to be careful.

This is where I have my external meter connected.

While staring at the schematics I noted the HV should be 600V.    Mine is between 650 and 716 depending upon line voltage.  However, with the divider composed of the two 20K resistors and the 0.202 shunt,  that voltage swing shouldn't have any impact across the shunt.
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73 Mark K3MSB
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k3msb
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« Reply #58 on: January 30, 2018, 08:27:40 AM »

beer, hot wings, nachos

All basic food groups!
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73 Mark K3MSB
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« Reply #59 on: January 30, 2018, 09:38:50 AM »

Only takes 0.05 ohms of contact resistance between the metal chassis and the ground lug and the 0.202ohm shunt is 25% too high.  This will cause the PA plate current to read high.  Soldering a ground wire from the shunt ground lug (even solder to the wire on the resistor) to the ground lug at the switch will eliminate this problem.

Fred
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N1BCG
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« Reply #60 on: January 30, 2018, 09:40:31 AM »

Are we collectively sure that the Valiant plate current meter reading is correct and can be confirmed with an external meter in place of the jumper on the accessory jack (intercepting the plate circuit)?

If that's the case then it's really just a matter of determining why the current is high. Test the 6146 screen voltage. R16 is a large 12k resistor that could have drifted in value.
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KA2DZT
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« Reply #61 on: January 30, 2018, 09:48:24 AM »

Are we collectively sure that the Valiant plate current meter reading is correct and can be confirmed with an external meter in place of the jumper on the accessory jack (intercepting the plate circuit)?

If that's the case then it's really just a matter of determining why the current is high. Test the 6146 screen voltage. R16 is a large 12k resistor that could have drifted in value.

Don't think it's reading correctly.  He said, in a recent post, that the meter is reading 500 ma while the test meter is only reading about 335 ma.

Fred
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N1BCG
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« Reply #62 on: January 30, 2018, 10:31:09 AM »

Only takes 0.05 ohms of contact resistance between the metal chassis and the ground lug and the 0.202ohm shunt is 25% too high.

Agreed. And that could also be within the margin of error for the resistance measurement of the shunt resistor or the resistor itself. Running a separate ground wire is logical, but it would be better as a test than as a solution.

I have a digital meter and I doubt that its accuracy is that good at low resistances simply because it uses such low voltages for testing. It's very easy to get an erroneous reading unless you're dumping a bit of current through the test component so that the voltage drop can be more accurately measured.

Yesterday's test had a DVM across the Viking meter (which is the same as across the shunt) and it showed 64.4mV while the Viking meter read 335mA. So, R=E/I (0.0644/0.335=0.192 Ohms) The caveat is that you also had another DVM measuring current in series with the Viking meter. Could you try that again with just the Viking meter showing current and a DVM reading voltage across the meter?

Theoretically you should see 60.6mV across the Viking meter when it reads 300mA (0.202*0.300). I'm dismissing the Viking meter's 20 Ohms for simplicity.
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k3msb
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« Reply #63 on: January 30, 2018, 10:51:36 AM »

Quote
caveat is that you also had another DVM measuring current in series with the Viking meter.

Yes, and I mentioned that in one of the above posts.   BOTH the DVM and Johnson meter were across the shunt,  so the Johnson meter reading would not agree with the external meter across J8.

Also, regardless of whether the Johnson meter read as expected,  the voltage across it was always what was expected based upon it's deflection.

Tonight I will run the new ground wire.   I'm not sure where on the chassis the meter switch is grounded,  but I know I didn't check that particular ground.

Quote
Theoretically you should see 60.6mV across the Viking meter when it reads 300mA

I tried this for 500 mV,  but I can certainly try for 300mV.

This morning I placed an order for a 0.2 ohm shunt resistor;  not 0.202 but that's the closest I could get.  Insanity momentarily gripped me as I considered paying $29 for next day delivery;  but then I realized I wouldn't have any money left for beer, nachos, and wings, so I elected a cheaper shipping method.   
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73 Mark K3MSB
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« Reply #64 on: January 30, 2018, 12:44:20 PM »

You need a Wheatstone Bridge to accurately measure the 0.202ohm resistor.  I have 4 of them.  You don't need to waste time playing with all the DVMs.

Probably didn't need to order more shunt resistors.  Anything you order may not be exactly 0.2ohms anyway.

Does the meter read correctly on the other ranges??  Is it only the PA plate current that reads high??

If it is only the PA plate current that is reading high,  the problem is the ground like I told you.

Fred
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Ralph W3GL
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« Reply #65 on: January 30, 2018, 06:06:36 PM »

You tellem Freddy, just keep that FMing under control.....

W3GL... Grin
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73,  Ralph  W3GL 

"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other"     Ed Morrow
KA2DZT
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« Reply #66 on: January 30, 2018, 06:15:55 PM »

You tellem Freddy, just keep that FMing under control.....

W3GL... Grin


Hi Ralph,

Fixed the FMing years ago.

Fred
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k3msb
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« Reply #67 on: January 31, 2018, 08:31:47 PM »

Tracked the issue down  Smiley to a bad solder joint where the shunt connected to the terminal strip.    Which I checked before..... Roll Eyes

Johnson               External
Meter (mA)          Meter (mA)
100                      150
200                      230
300                      310
400                      390
440                      420

These were on 160M.

I reflowed the solder connections on the meter switch etc and that did not significantly alter any readings.

I will exercise the other bands tomorrow.
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73 Mark K3MSB
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« Reply #68 on: January 31, 2018, 09:06:03 PM »

Nice! The 300mA range is the most important and that's where the meters seem to agree. I wouldn't strive for the book values of current, particularly since your voltages are so high. I use 300mA for AM and 330mA CW. No sense in stressing out a 60 y/o transmitter.
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KA2DZT
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« Reply #69 on: January 31, 2018, 09:38:50 PM »

Was that cold solder connection on the ground side or the high side of the shunt??

Anyway glad you found it.

I based my comments assuming the solder joints on the shunt were properly soldered leaving only the ground to the chassis as the problem.

Fred
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k3msb
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« Reply #70 on: February 01, 2018, 07:58:17 AM »

The bad joint was on the high side of the shunt.   My 0.202 ohm shunt are 4 resistors in parallel;  a 0.2 ohm resistor is en-route from Mouser so I'll revisit the shunt next week.

I'm not sure the VFO is reading correctly so I may need to futz with that a bit as well.

Next week I'll do the driver mod Clark suggested.   There's also a mod for the VR tubes so that the Modulator current reads correctly;  I'll see about doing that next week too.  Audio mod will come afterwards.

I plan on being on for the AM Rally this weekend,  so today and tomorrow will be spent getting a 2nd station up and running with the Valiant being the transmitter.   I like 160M DXing,  but I've never been on 160M AM so we'll see how that goes.

Clark and Fred,  thanks so much for your help..... and keep reading this thread.... no telling what lurks in the future!
 
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73 Mark K3MSB
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« Reply #71 on: February 01, 2018, 08:57:35 PM »

Moved the Valiant to the operating position in anticipation of trying it out in the AM Rally.

Turn on the HV and blowing fuse F1 to the LV transformer T2 like candy.    Put it back on the bench,  same thing.     Did absolutely nothing to it.

Grid drive is set to 0 so I'm not overdriving it;  in fact, I never go key down to tune up!  

Tried it on 160, 80, and 40.   Same thing.     I removed J8 and that had no effect.  

 Huh Huh Angry Angry
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73 Mark K3MSB
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« Reply #72 on: February 01, 2018, 09:33:35 PM »

What size fuses are you using??

Still blows fuses with J8 out??

Let me know

Fred
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k3msb
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« Reply #73 on: February 01, 2018, 09:46:23 PM »

Using the recommended 2A fuses, yes with J8 out.    I'm real glad I moved that 2A fuse to a chassis mount fuse holder!

I was really frustrated and just a tad PO'ed, so I just put the radio back on the bench and called it a night.   I take a look at it on Saturday.

I noticed that the VFO was slipping so I was playing with it, removed the dial face etc.   Readjusted the pointer, reinstalled the dial face and tried to tune up.   Started blowing fuses as soon as I turn on the MAN/PTT switch;  don't even need to key down.

With J8 out I'll start by isolating the smoothing choke and see what that shows.

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73 Mark K3MSB
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« Reply #74 on: February 01, 2018, 10:15:49 PM »

I looked at the schematic.  I see three fuses.  Two 8amp fuses on the main AC line and a 1.8amp fuse on the primary of the main power xfmr.  Exactly what fuse are you blowing??  I'm not seeing a plate fuse but I'll look again.

One thing you should know,  those 866 HV rectifiers are a common cause of shorts.  If you had the xmtr on its side or upside down, those 866s will short as soon as you put voltage on them.  Mercury rectifiers have to be kept in an upright position at all times.
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