Author Topic: KNIGHT KG-625 VTVM issue  (Read 413 times)

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Offline CramboneTopic starter

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KNIGHT KG-625 VTVM issue
« on: July 02, 2023, 11:48:06 pm »
 KG-625 VTVM issue
I’m having an issue with this VTVM but here is a little info on the unit and what was replaced first.
All resistors with the exception of a 91M as I dint have one have been replaced with new Metal Oxides since I had to lift an end on most to test I figure I would replace. The only Electrolytic Cap was replaced 20uf 450v. All pots have been removed, opened, cleaned. Tube sockets have been cleaned and all seem snug.
I also tried and tested 3 ea 12AU7 and 2ea 6AL5 so I don’t believe the tubes are bad. I only have a Sencore Mighty Mite VI to test with.
I also carefully cleaned all the contacts on the switches.
OK so here is what’s happening when I try to calibrate.
I did check all the voltages shown on the schematic, they are a bit high but I’m using a digital Meter so I expect that. The one’s I do have a ? On are pins 3 & 8 on the 12AU7. Schematic shows 1.6v and I’m seeing 3.4v on pin 8 and 3v on pin 3.
The meter zeros mechanically fine.
When I turn the meter on the needle stays pegged right but when I connect the probe too the ground I can zero with front control.
The 1.5 VDC calibrates no issue
The .5 VDC calibrates no issue
The VAC calibrates no issue
So the Ohms oh the Ohms. I put in a new tested C battery. Ok it zeros fine and then aligns to the infinity mark on the right just fine. But when I try to test ANY size resistor it just pegs the meter left????
I should also mention I checked every wire and connection was correct per the build manual.

1. why does meter peg right with nothing hooked up? Is this normal?
2. What can possibly cause the Ohms not to read?

What can I be missing?

Link to manual file is too large to attach: https://elektrotanya.com/allied_radio_knight_kg-625_vtvm.pdf/download.html
 

Online floobydust

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Re: KNIGHT KG-625 VTVM issue
« Reply #1 on: July 06, 2023, 03:51:58 am »
I don't know what the crickets are about. Are you sure you are setting Ohms function zero and full scale properly? I'm like how does the needle read past the top with a real resistor...  :-// To confirm- it's a reverse-reading meter: zero ohms far left, open-circuit far right?
What ranges is this happening on? Here is SCH for those that want to follow, it's not complicated although following the switches is surely a form of torture...
I would be measuring the plate voltages with it on Ohms zero and open and a test resistor, and what is across R23 27k to see if the middle bias point -50V is reasonable.
 


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