Viking 2 CDC capacitor wiring

[N9axl]

I'm getting around to replacing the drive pot. It appears that there is no way to remove this without removing the entire front panel.  The nut on the panel face comes off but there is a second nut inside and there is no clearance to put in a wrench.  There is a bracket holding this but no clearance to get at the nut.  

I removed the front panel after disconnecting the meter.  I then cleaned the front panel, dismantled the meter down to the movement and cleaned/ adjusted glass. It looks good with no obvious physical damage.  Reinstalled meter. Will replace bypass caps and reinstall.

I am wondering about putting some diodes across the meter in parallel to protect the movement from voltage surges. Is there supposed to be some kind of shaft coupler on the exterior of the Tank tuning shaft holding all that to the panel.  There was just the shaft going through the hole. That screw on the knob on the pointer seems sort of wussy to turn all the mechanism.

Installed new drive pot - 5w 25k wirewound as recommended.  Knobs currently soaking overnight - I should clean them as long as they are off. I also need to restring coupling which is off the pulley.  I have no dial string so I need to find an alternative - fishing line? Boot laces?

I also replaced r23 and confirmed r19 is at correct value.

[DMOD]

I also need to restring coupling which is off the pulley.  I have no dial string so I need to find an alternative - fishing line?

You might try this or some 60lb fishing line:

https://www.tubesandmore.com/products/S-M75


Phil

[N9axl]

Thanks.  I figured out when I did this that, at some point, someone removed that drive bearing coupler -- the one on the front panel under the tank circuit -- so I will need to find one of those.  The meter is reinstalled, but I still have to check it for accuracy.  I figure someone in the past 50 years has twiddled that little screw on the front of the meter. I'm not sure if that's in the original position.  Something else to research. Otherwise, we will keep moving along with this.  The shunt resistors came yesterday so those nichrome wires are outta there.

[Pete, WA2CWA]

  I figure someone in the past 50 years has twiddled that little screw on the front of the meter. I'm not sure if that's in the original position.  Something else to research.

The screw adjustment on the front of the meter is to set the resting meter needle to zero with power off.

[N9axl]

Thanks.  It seems to be coming along.  I turned this on yesterday -- just filaments without the HV installed and the meter popped up to about 5ma and stayed that way on all settings -- grid, oscillation, etc.  Clearly not right but I will keep working away on this.


While I continue to work on the electrical issues I'm cleaning up small mechanical ones -- like replacing the set screws on the knobs with stainless steel with allen head. The originals are all rusty and nasty.  A minor detail - especially when this thing doesn't work -- but a break from working on the other parts.  I also have my ceramic mike element delivered today so I will be fixing my D-104.

[Jim, W5JO]

  I figure someone in the past 50 years has twiddled that little screw on the front of the meter. I'm not sure if that's in the original position.  Something else to research.

The screw adjustment on the front of the meter is to set the resting meter needle to zero with power off.

And if the meter is properly balanced and movement is free then the needle will remain at zero either horizontal or vertical positions.

[N9axl]

Ok. I replaced those nichrome shunts. When I put a crystal in, set it up, with the HV off and out of course, I get about 2 ma of buffer current. I also saw about 2ma of oscillation.  On the ts-820s across the room I am picking up a tone.  So it is oscillating...just not at any meaningful useful level. I will keep tracing this out this weekend and see what the deal is.

[KB2WIG]

I think that you will find the Osc and Buffer settings a bit critical to adjust. At least on my VK2 they are. Just try the graph settings for starters.

klc

[DMOD]

Ok. I replaced those nichrome shunts. When I put a crystal in, set it up, with the HV off and out of course, I get about 2 ma of buffer current. I also saw about 2ma of oscillation.  On the ts-820s across the room I am picking up a tone.  So it is oscillating...just not at any meaningful useful level. I will keep tracing this out this weekend and see what the deal is.

Those currents are too low with your high Low Voltage Supply voltage.

What does the meter show with Meter SW in GRID position?

Did you peak OSC and Buff with OSC and Buff tuning controls?

Let's check meter accuracy. What are the voltages across SH3 (5.1 ohms) and
SH5 (2.2 ohms) when keyed?

You should see approx. 40 mV across SH3 and 33 mV across SH5.

Waat is your bias voltage to the buffer grid at the bottom of R23 (47k)?

[N9axl]

no peaking. goes to 5ma and stays there on all scales.

on sh3 22 millivolt sh5 2.3  r23 voltage is -23.

r15,r16,r17 sh4 all checked a2nd within tolerances.

[DMOD]

Rather than taking up anymore bandwidth om here, send me an email and we'll try some more checks.

i am not convinced the OSC is oscillating.

Phil

[N9axl]

What I realized last night was that the meter glass is loose and was in the way of the meter. When I held the glass out of the way and fired this up the oscillator read 8ma immediately. When I switched to buffer it dropped to zero.  I will need to remove the meter and shim the glass in place.  From there I can continue to check on this and see else needs to be done.


Now that this is making progress and the weather is warmer I intend to strip and paint the case. This is just for me and I have no intention of selling so I will strip it, prime it, and spray paint it grey.  Good enough.  I still need to find feet. I only have two.

The other question is this CDC has push to talk. My D104 has only the audio input no switch.  It's fine for a Heathkit or some other non PTT rig. I am assuming I can just turn the plate switch off and on to modulate.  I have another D104 with a PTT switch but I need to get a new element.

[Pete, WA2CWA]

The other question is this CDC has push to talk. My D104 has only the audio input no switch.  It's fine for a Heathkit or some other non PTT rig. I am assuming I can just turn the plate switch off and on to modulate.  I have another D104 with a PTT switch but I need to get a new element.

Flipping the plate switch on and off to transmit is fine. Why don't you just switch D-104 heads?

[N9axl]

I will think about that. I fixed the meter and now see about 10 ma of oscillator current. I see no grid or buffer current. I will need to check some voltages and see what's what.  It's moving in the right direction.

I'm trying to understand the circuit. The 1800 ohm R24 resistor seems to be the grid leak resistor but it seems too small for negative -77 volts and the nominal 2.5 ma grid current.
77/2.5=30.8 kohm

In any event it will be replaced as all the resistors in that voltage divider network are high.

R15   Stock value 1500/actual measured value 1613
R16.   820/908
R17. 2700/ 2999
Sh4 5.1/ 6
R24 1800/2351

[N9axl]

One or two people wrote and said what's going on with this project? I didn't know people were that interested, but I appreciate it. OK - After several emails with Phil AC0OB- thanks- and checking of voltages, I cleaned up the connections under v5. I replaced one .005 bypass cap. I also replaced c20 a silver mica cap - it was new but I figured it might be bad since I was having no buffer current. I also just reheated all the connections in case there was a cold solder joint.

After that I immediately got buffer current at 5ma. I figure it was a bad cap.  Still no grid current. That's the next thing to figure out

This is a step in the right direction. This weekend I intend to check everything over and see what the next steps are - and I need to figure out the tuning procedure.  I still have a lot to do with this as well as the minor things like repaint the case and get some cabinet feet.  On that score - I will soon have access to a 3D printer with a digital scanner attachment. Not mine- it's around $2500.

Basically, put the foot I have in there, a laser scans it, and the 3-d printer does its thing. I'd prefer the original but I've had no luck finding any online. Memorial Day weekend will probably be in the backyard doing paint removal and repainting. I have to find some proper paint for this if I can figure out the color.