The AM Forum

I'm getting ready to replace these electrolytics.  The first one 15/15 450 is connected across v10.  This is on the left. Green and red positive wires to v10 pins 3 and 8 and common negative to 6AL5


The second 15/15 150   This is on the right. The two positive wires seem to run under the relay. And the negativewire to a terminal strip on the right side of the relay.a second negative to the 6al5

I've checked the schematic several times and this appears to be correct.  Before I solder this all together would someone be willing to confirm my thinking here. Johnson isn't always consistent between schematic and reality.

The photo by the way doesn't do justice to the fine capacitors which I had Chuck Hurley run up for me.  These are lovely, highly professionally made, and well labeled with long leads.

Hi,

I don't have the CDC but it looks basically the same as a regular V2. Grab the assembly manual for the regular V2 and check step 41 and 42 on page 28. The original 450V tubular was a 3 wire cap, 2 pos and one common neg wire.  I replaced mine with 2 axial caps exactly as the original was installed. Positive end of one cap to pin 8, positive end of other cap to pin 3 of 5V4 X10. The negative ends both went to the terminal strip X22. The 150V cap (C12 - 13) was a four wire cap. Positive wires were connected to a ground lug close to R13, negative wires of the cap to pins 6 and 7 of the 6AL5 X11. I used a couple of radial caps for these and used the ground lug at the 6AL5 instead of going half way across the radio.

Your 450V sounds like it could be okay if you are putting your common ground connection at the 6AL5 to a ground tab or ground tie point? Your description of the 150V doesn't sound right to me. You might want to review your wiring against a CDC construction manual if you can get one. Also, I'm certainly no expert, so you might want to get a few more opinions on it too.  :)

Good Luck and 73
Kevin KD1NW

+1, your description doesn't match the schematic unless the 6AL5 pin is grounded. Go with the schematic, it is correct. For what it's worthless, I'd go with 20uF caps, a little more filtering wouldn't hurt. IMO the V2 is the best AM transmitter Johnson made, it lends itself nicely to audio mods and of course external peak limiting like an Orban AM Optimod for the "professional" ham (;->) is pretty much essential if you don't want that piss weak hyellowy audio. Oh and of course it has plenty of knobs I like to play with.

Thanks. The assembly manual on Bama has no pictures or figures.  Is the x22 terminal strip the one to the right of the relay underneath the length of coax?

.

Here's the picture. The 150 v on the right - positive red and green, one negative to the terminal strip (x22?) on the right, the other negative going to the 6AL5.  The cap on the right is the 450 v with two positives and a common negative going to v10 and the 6AL5.

Hi,

Is that the way it was originally wired? Because it sounds wrong. None of my wires for the 450V go to the 6AL5 and none of my wires for the 150V go to X22. Your 450V cap should only be associated only with connecting to X10 and X22. Positive terminals to 5V4G (X10) and any negative terminals to X22. Your 150V cap should only be associated with the 6AL5 (X11). This is 'reverse' connected. Positive wires to ground and negative wires to the 6AL5 pins. Your description has wires from your 150V cap going to X22 which is not right, in addition you have your negative wires of your 150V going to ground which is not right, the cap will be damaged. At great personal risk, I've attached a couple of pics of my shoddy workmanship :P . But I hope it can help you see how it's laid out. One is a pic of the whole underside with some annotations so you can see where things are in relation to each other. The other is zoomed in a little more on the 6AL5 caps. My radio is not the CDC version, so I don't have the relay.

Thanks 73
Kevin - KD1NW

I posted yesterday but apparently it didn't "take" so here is the essential again. The schematic is correct, it's your description that isn't, or somebody wired it incorrectly with the grounds in the wrong place. Instead of what are grounded tube socket terminals they should go to ground lugs on the nearest terminal strip(s). BTW, a little more capacitance for better filtering wouldn't hurt, say about 20uF.

Thanks. It was backwards. As it now sits the 150 volt has negative across the 6al5 pins 2 and 7 - it's hard for me to count the number - and  positive to ground - the red and green wires going up under the relay. The 450 has negative at x22 fourth terminal going from the back of the chassis and positive at v10 at pins 3 and 8 counting clockwise from left. The appears now, finally, to be right.

The lesson here: assume whoever last worked on this radio, me last week or Susie Assembler in 1955, did it wrong!!!!



My workmanship is equally shoddy. 

It sounds right to me now, unless anyone disagrees.

To count your pins, on the 5V4, the base is keyed with a notch. With the tube plugged in you can see the notch from the ceramic socket where you do all your soldering. Count going clockwise from the notch. Actually on mine the numbers are right there on the ceramic bases.

The 6AL5 is a little trickier, it's keyed by a wider spacing between pins 1 and 7 which is sometimes hard to see. Start with the rightside pin on the widely spaced pins and count going clockwise. You can pull the 6AL5 too and should be able to see the widely spaced pins a lot easier. You can also verify it by using the schematic and the tube socket connection diagrams in the manual. It doesn't hurt to do both.

And no worries on the workmanship. My takes is that if it's functional and safe then fine. I can always go back and redo it when my skills improve or the next person that gets it can do it to their liking. I hope you don't need anymore photos, I'm going to button it back up and that's a bunch of screws on the bottom plate  :)   

Also, a couple of tips I've learned the hard way, take lots of photos before doing any work so you know how it was hooked up originally. And only work on one or two component leads at a time so you don't lose track of your connections. Be safe and have fun.

Good luck and 73
Kevin - KD1NW 

Thanks much. This is done underneath. At this point what's left is to put on a new power cord, check the replaced caps, put the oil filled cap back in and button up the bottom.

need to restring on top. how hard is it to,remove the face plate?

I need to find the #40 bulb for the filament light, two feet, and various tubes. Off to Fleabay I go.

Here is a new "gotcha" on the cdc Vikings.... if you are leaving in the selenium rectifier be aware that it's clearance to the bottom cover of the transmitter is very minimal....  the fins are at B plus and if you are not careful they can contact the transmitter bottom cover thus shorting HV to ground.... 

The selenium can accidentally get rotated and come way too close to the cover.

73, Tom

In close clearance situations a piece of black vinyl electrical tape on the cover put the Alfred E. Neuman to it for me. BTW I hate solemnium rectumfriers that have a bad habit of going open and replace them with sillycone dymodes. That's a common problem with the R-390 receiver, then some of the T-R protection relays don't work leading to a possible uh oh.

I have already replaced the selenium rectifier with a resistor diode combo.

This all worked.  I finished checking the caps and then installed a grounded power cord. With just the LV rectifier installed - we have filament voltage and everything came on without drama.

 Good progress.  I now need to get the HV rectifier tubes and the 6146 tubes installed.  Fortunately this came with the 807s left in it so that's one less thing to locate. I also need to find two feet and the filament light bulb.

Before I do that I plan to build a chicken stick so I can ground the caps etc once the high voltage comes into play.

Great, thanks for the update. I'm glad to hear things are coming along

Thanks. I have all the tubes either here or on order. Only 1 6146 available so I need to get that. They won't be matched.  I may have a 6146b somewhere but I dislike mixing tubes.



. And as a hint and tip - I went to Lowes looking for a short piece of PVC tubing. No good since 5 feet seems the minimum.  I then saw the lawn irrigation section.  They sell a one foot piece of pipe threaded.  There is also a separate valve that threads on. All for $2.  I popped out the center of this valve and it took the small eyebolt I had perfectly.  Soldered on an insulated wire and good to go.

Now if only the audio on my SBE 34 was as good to go.  No audio output. Assume the PNP audio output transistor that drives the speaker has failed.  I have a spare but it's just one more project.  Just a scratchy noise when I turn the volume and no sound when hooking up external speaker.  

6146's in parallel don't have to be matched.


Hang a scope lead on the center wiper of the volume control to see if you have audio wiggle. Then, working towards the speaker, test each stage for audio output.

Now, I did actually fire up the CDC.  The filaments lit up but I saw nothing on plate voltage or anything else. Also no drama with blown fuses, sparks, etc - always a good thing. 

This was done with only one HV rectifer tube installed since I am waiting on the other.  A really dumb question, but would having only one account for no oscillator current, etc?  I'm still not sure about how to set this up. I put a 7.103 Crystal in position 1 and tried to set it up with the charts in the manual, but not sure I have those right.  My manual is fuzzy Repro. I made sure a key was in the jack.

My plan here is to use this solely on 40 meters as that is all I have antennas for.



I have no scope. I need one - or actually I should fix the Heathkit scope I have in the corner.   I plan to check the voltages across the audio  -- I have the maintenance manual so I know what they should be. I'm thinking if the audio output transistor to the speaker is blown that's the issue.  

You can get some really professionally created manuals from several sources.  It would be worth the minimal expense.

I plan to do that. I need to clarify the issue of the octal socket X12 in the back.  In my Ranger this is essential for the radio to function that this plug be there. The manuals I have say nothing about this.

K,

Look at this attachment. It shows which rectifiers power which ckts.

I solid stated the HV with a bunch of 1N4008s. I also added an inline fuse for the low voltage transformer. Replacement of the transformer would be expensive.

klc

Today i fired this up and see get no oscillation current, no buffer, no voltage between pin 3 and ground on the VFO plug. A low b+ issue since there should be 300 volts. Now on the 5v4 there was 380 volts between pin 3 and ground so t2 is working.

In earlier discussion pin3 was seem as correct.

However,the pin out diagram for the 5v4 shows the plate is on pin 4 not 3. It would seem that pin 4 is the correct tie point for the positive of the 450 volt cap. Pin 3 is not used in a 5v4.

Am I thinking about this correctly?

I looked at the Viking II schematic in the manual.  It does not have pin numbers on the tubes, so it would be  necessary to use a tube manual to determine the correct pins if you are not familiar with each of the tubes.

The 5V4 low voltage rectifier has two plate pins, 4, and 6.  One of each of these pins should connect to each end of the high voltage winding of the low voltage power transformer.  There should be NO other connections to these pins.   

The filament and cathode of the 5V4 uses pins 2 and 8.  These go to the five volt winding of the same transformer.  One of these pins connects to the low voltage filter choke.  That is the pin where the positive lead of the 450 volt electrolytic capacitor should be connected.  The negative lead of this capacitor goes to ground.  The assembly manual may clearly reveal which of pins 2 or 8 is used for this connection, but it really does not matter, as long as the choke and filter capacitor are connected to the same pin.

There are no connections in the 5V4 tube to pins 1, 3, 5, and 7.  If any wires are connected to these pins, they are just being used as tie points for other parts of the circuit.  A check of the assembly manual would reveal whether the connection you see is stock or a modification.  The CDC version power supply is likely very similar to the more common Viking II.

The Viking II manual is available on the BAMA site or the Edebris mirror site.

The wiring seems right. I am wondering if I misunderstand how to tune this. I have a 7.200 crystal in position 1. This isn't tuning on 40 but on a different band using that crystal. I need to figure out the proper settings and what band a 40 meter crystal would be used for.

Page 26 of the CDC manual shows you the pin connections for each tube. Regardless of who says what or when, you should always confirm when a reference is made to connect this to pin X, connect this to pin y, etc. Take the info from page 26 and mark the pin numbers on your schematic. You should also review pages 21 and 22 which have some very useful voltage, current, and resistance measurements under various operating conditions.

A 7.200 MHz crystal at the very least is used for 40 meters. If it's an overtone type crystal, it can also: 7.2 X 2 =14.4; 7.2 x 3 = 21.6; 7.2 X 4 = 28.8. Obviously, X2 and X3 are out of the amateur band but if it's an overtone-type crystal, you could set the bandswitch to 10 meters and tune up on 28.8.

Also read the tuning details starting on page 9. Very useful information.

Thanks. I'm getting a 20 amp variac. I hated to spend $109 but I'm at the point it's a necessity.

I have the Viking 2 assembly manual so plan to simply work through that. Pages 34 and 35 are the instructions for when it is fully assembled. Turn on LV with no tubes, turn on HV with no tubes, ok that didn't blow up, put in the rectifier tube, etc etc. I also ordered a new 6au6 tube.  Actually 4 since that got me free shipping.  I have a tube tester so I will run everything through that also.



I think I can work through that and find out where the issue is.  Working with this at 20 percent power on a variac will make it somewhat easier I think - I won't worry about clobbering myself with 700 volts.  I feel sure this is a fixable issue given enough time and patience.

If you run it on a Variac, there may be circuits that won't run properly or not at all. Plus, you can't get accurate voltage and/or current measurements unless you run it at the rated AC voltage. If this transmitter is a Viking II CDC, I would use that manual. If I remember correctly, I thought the CDC was only sold as a factory wired unit so having an assembly manual for the plain Viking II may not accurately provide the correct and necessary information for all the circuits in the CDC. As they say, use the right tool.

When diddling around voltages, wear a long sleeve shirt, keep one hand in your pocket, and have some insulation under your feet if you're standing on concrete or a grounded surface.

Good advice which I follow. I started checking resistors this morning and found that r29 had drifted up from 470kohm to almost 800kohm. I will keep plugging away at this and I greatly appreciate everyones advice.

Did you not receive the CDC manual I sent via private email?

It has the schematic as well as tube pin outs.

The Viking II-CDC is a factory wired unit.

Recall that I suggested you check the junction of C11 and L2 and trace from there to the junction of C10 and the other wire from L2. I also stated that some pins on the rectifier tubes are not internal tube connections but interconnection points.

Pins 2 and 8 on the 5V4 should have over +350V DC on them and connect to both C11 and L2. Pins 4 and 6 on the 5V4 have HVAC on them. Pins 3, 5 and 7 on the 5V4 may be used for interconnection points.

Trace them out.

Phil - AC0OB

Oh yes I see that now. Thanks. I'm following through that.  I do see about 380 on those pins as you suggest. I also checked the positive end of r13 and got 780 volts. There is about 270 at the tap. I will just continue to trace through this as suggested and see why there is no oscillation, no meter indications of any kind. It seems to me that the power supply circuits are doing what they bare supposed to. I just have to figure out why that voltage isn't actually doing what it is supposed to.

I truly appeciate everyone's assistance. I realize my questions are, for those who know what they are doing, somewhat boring and simple, but I'm learning so please bear with me. 

Let's take one step at a time.

1) How much voltage do you have on the terminal strip up in the audio section where the red wire meets the terminal lugs? That's LV (325V+) for the audio section.

2) How much voltage do you measure at the bottom of R20, the 100 ohm resistor? That's LV (325V+) for the OSC and Buffer-Driver section.

If you don't have LV (325V+) at these points, then you may have a LV wiring problem.

If you do have LV (325V+) at these points, then you may have a metering problem or a different problem.

Also check the Key circuit at the cathode of the OSC, pin 7, and see if it is getting grounded when the CW/Phone switch is in the CW position. In the CW position, you should get some grid current on the meter when the Meter Switch is in the GRID position.

When there is no key in the Key Jack, the cathode of the OSC gets grounded in the CW position, assuming you have a good crystal. And check to see if the crystal position and the Crystal Switch match.

Disregard the HV and anything else until you clear the LV situation. The LV is on all the time when the Main Power (Fil.) Switch is up. So you should NOT have to key anything to get LV.



Phil - AC0OB



 

Thanks. Checked both of these.  My eyes aren't great but the red wire looked like it was the third from the end going from the center of the radio.  I saw 775 volts there. I checked r20 and saw 375. I will check the other item this weekend.  I do notice that the meter glass is broken so it's possible that there is a problem in that it hasn't been a sealed unit.

Perhaps I should replace this? I ask because I see a Johnson Viking 1 meter on fleabay right now, but I don't know if that will work. I'm not sure how I would test a meter.

Checking a meter movement can be a bit tricky, so don't do anything before telling us what way you plan to test the meter.

Fred

I intend to do nothing to the meter until I have checked out everything and eliminated everything but the meter. I agree its a tricky job I want to avoid if possible. I would have o learn how to do it anyway.

Like the man says - one step at a time. It appears,based on limited testing, that this is producing LV and HV which is something.

Put the transmitter on the bench and Remove BOTH 5R4's.

Do not attempt to key or flip the transmit switch. It just isn't necessary so keep it "off."

With the wiring (bottom) side facing you, orient the chassis so the 807 Modulator tubes are on top (or 6146's down). The Front Panel with the knobs and controls will be to your left. The audio terminal strip is in the upper left area. This terminal strip lug with the red wire on it should have LV on it, no more. This is with just the filament switch on.

There is no way you should see 775Volts on that terminal lug with the red wire. Please recheck your voltage here.

The voltage on the bottom of the 100 ohm R20 resistor is high but that may be your resting LV voltage without a load. The same voltage you saw here should be the same voltage you should be seeing on the red wire in the audio section.

Even though I have good eyesight, I still use a bright flashlight and a 4" magnifying glass.

Phil - AC0OB

It is 375 volts in both locations.  My mistake. I measured to the other red wire to the terminal strip to the right next to the 807s the first time.

This time I measured to the terminal strip in the upper left with the bright red plastic wire in the wiring bundle coming along the front bottom of the radio.

OK, whew, that's better. :)

Now put the oscillator tube and buffer-driver tube in, and with the CW/Phone switch in CW, turn the Crystal Switch to the second position with a crystal in the first crystal socket.

Remember, the first position of the Crystal Switch selects the VFO, so the second clockwise "click" of the Crystal Switch selects crystal number 1.

Make sure you have the FREQ SW in the 5.8, 8.4 position for your 40 meter crystal.
Set the Meter Switch to GRID and turn on the Main Power (Fil.) switch. After warm-up, turn the crystal and buffer tune knobs to get a reading on the GRID, as per the manual.

Phil - AC0OB

Getting no joy on this. I checked the voltages on the 6au6 and found
Pin 1-0
Pin 2-0
Pin 3-0
Pin 4-0
Pin 5- 383.5
Pin 6 - 379
Pin 7-29.24

I did check the tube in my tube tester and it tested good.  Admittedly, it's an old Jackson 648 which I haven't calibrated, but it checks for shorts and it seems all good

These are DC meter readings at the tube socket ?

What is the voltage on the filament at the socket (AC) ?

Is the tube WARM to the touch?

Looks to me like you might have a problem in the filament wiring...
,

N9axi & others:

The force is strong to bring the new puppy home and plug it in. Lets see how much magic smoke pours out! Unless the seller can prove all is well on all bands and you are there to watch for said "magic smoke"; don't plug it in.

First: Get a skizmatic of said magic smoke producer.
Second: Enlarge said skiz to at least a 3 foot X 3 foot skiz.
Third: Tack/Tape said skiz above lobotomy work area.
Fourth: Check every wire, passive component, tube socket, all additional  extra great ideas, etc. Is it all there, wired correctly?
Fifth: Throw all old electrolytic caps into the dumpster, replace crap caps with new. Include BBOD's to cap list.....dumpster item.
Sixth: Mark up skiz with notes, repairs, crappy great ideas.

At this point you might be ready/safe to plug in said smoke producer. Ready oneself for anxiety attack, turn on power..........
Seventh: READ MANUAL......there might be some good information as how to tune/load/operate said smoke producer.
YMMV...........

Craig,  

Which 6AU6, the OSC or the first audio amp?

http://frank.pocnet.net/sheets/049/6/6AU6A.pdf

Like Pete said:
Keep 5R4's outta here until we get grid current. :D

Put your meter on AC and check ACROSS pins 3 and 4 for about 6.5VAC.

If you have AC, ground pin 8 of the Auxillary Jack momentarily and see if you get grid current.

And make sure the Drive pot is not above 2.5.

Take one aspirin and report back. :D

Phil - AC0OB

Pins 3 and 4 had 6.5 volts AC. This is the 6au6 oscillator v6 directly in front of the Crystal sockets.  If by auxiliary Jack you mean the VFO octal socket - a jumper from pin 8 to ground did nothing but trip the GCFI socket in my shack. I should not have it on this GCFI but it's how the room is wired. 

Pin 8 of the X12 jack is the Key line for the OSC and also keys the VFO.

Were you counting the pins from inside the chassis or outside the chassis? You have to count from inside the chassis starting with the index tang and count clockwise. Trace the wiring on pin 8 of X12. A gray or slate-colored wire should be on the left side of the coil that connects to pin 8.

If you have nothing plugged into the Key Jack the cathode, pin 7 of V6 the 6AU6, should be grounded when in CW mode and oscillate.

Turn off power and do an Ohmmeter check from chassis to pin 7 of V6. It should be close to 5 ohms when in CW mode.

Phil - AC0OB

Yes. I saw around seven ohms between chassis and pin 7 in both cw and phone positions with power off and plate switch in the on position.  I checked the resistance of the shunt resistor and saw it as infinite.

Now, the other day, per your earlier message, I did put in the oscillator tube, etc. etc. while leaving the 5r4s out - they are safe in a drawer - and , for a few seconds, did see grid current to about quarter scale on the meter. It then dropped to zero and stayed there.  The shunt resistor did measure about 5.1 ohms before.  I was told I should replace these already by a knowledgeable person but hadn't gotten to it. 

I truly appreciate your help with this.  It seems I may need to order some parts and, at any rate, work calls me so it may be a week until I get back to this.

Before you order parts make sure the Key Jack is shorting to ground when there is no plug in it.

The SH3 shunt IS 5.1 ohms.

You got somefin flaky going on there that you're going to have to patiently track down with the manual I sent you.


You can do what you want but in my years of rebuilding and upgrading, I have never replaced these low value shunt resistors in the OSC and Buff because they are usually 1 Watt types that just don't carry enough current to get hot.

Now, as a matter of maintaining meter accuracy, I do replace those nichrome wire SH1 and SH2 with 1% 0.2 ohm ceramic coated resistors because those Nichrome wire shunts have been found to be outa whack.


Phil - AC0OB



 

Yes I will check. I realized I didn't clean the Jack so it may be dirty. I did the switches and forgot that. Thanks.

Recall that  previously this is what I sent you in regards to potential OSC and Buffer-Driver problems:


However, one should only do testing and initial checkout with the 6AU6 Osc tube.

Good Luck.

Phil - AC0OB

yes.all  suggested parts are on order and will be installed per your comments. I am carefully checking everything over again. your help is greatefully appreciated and is being followed.

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.

You might try this or some 60lb fishing line:

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


Phil

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.

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

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.

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

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.

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

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)?

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.

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

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.

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

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

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.