Issues with recently acquired Johnson Viking 2

[WD4DMZ]

About 2 weeks ago I acquired a Viking 2. It was in unknown operating condition, the power cord was cut and there were no tubes in it. However, it was clean and had no water or burn marks or burnt smell and the price was right.

After adding a new 3 wire power cord and a complete recapping, some tweaking and general wiring inspection I put in a crystal and powered up into a dummy load. Voila!!!! Not only did it power up to rated output with the tubes I was given with it the audio reports with a non-amped D104 were great. A successful return to the air.

So, what are the problems?

First, the Viking transmits an even 1 khz above the 40 meter xtal frequency. The 7295 is at 7296 and the 7290 is at 7291. To check the xtals I put them in my DX60 and they were spot on. By the way, my 3740 xtal is on 3740 in the Viking so the issue is 40 meter circuit related.

Question... any ideas what might cause this and possible solutions?

Second... I also acquired a VFO122. It was pretty rough but looked ok inside. I plugged it into the back of the Viking and it lit up. Then, when I flipped on the HV there was a sizzling sound and the Viking died. Upon visual inspection, there is something that looks like a power resistor at the base of the HV choke L7 between the coil and the HV and it burned in two. Hence, no HV to the 6146s.

This appears to be a resistor as it is brown and has a yellow and purple band on it. However, I believe it is actually a VHF  choke L21. Is that what it is? What is the value of it? The manual justs lists it as a VHF choke.

As luck would have it, the gentleman that sold the Viking to me handed me a box of extra parts as I was leaving and fortunately there was an L7 in the box complete with this somewhat mysterious part and the two .01 1500v bypass caps attached. They were ok and I am back on the air.

Question 1: Is that resister looking component really a choke and what is the rating?

Question 2: What would have caused the component to blow when I attached the VFO and turned on the HV.

Rather than risk blowing my only spare part I am sticking with xtals for now.

I did power up the VFO on a separate power supply and it had a nice output and was close to calibration so internally it is ok.

Any advice and guidance will be appreciated.

Thanks, Rich

[Pete, WA2CWA]

L14, L16, L19, L20 and L21 are all the same VHF parasitic chokes. If you have an inductance meter, you can measure it. Most likely it probably around 5 microhenries @ several hundred mils. If you plugged in the VFO and there is a wiring problem on the Viking II accessory socket (I would verify proper connections to each pin) and the VFO didn't supply any drive, and your clamper circuit was not working probably, it's conceivable the 6146's were pulling excess current causing the choke to blow.

[w4bfs]

  what Pete said ...

AIRC Johnson and Heath did not get on the same page about the external vfo wiring ....close, but no cigar ... check it carefully ...gl

[WD4DMZ]

Good inputs, thank you.

Question on using a Heathkit VFO... If I put the DX60 in the tune position can I just take the HG10 output and connect it to the Viking 2 to see if it will drive it ok or will that damage the HK VFO?

Also, might either of you have any xtals for the AM windows you would care to part with?

Thanks, Rich

[WD4DMZ]

I have an opportunity to pick up a Heathkit HG10 VFO for a reasonable price. Looking at the schematic for the octal power plug it appears I need to move the B+, Filament and ground wires to different pins. I will not be using the Viking 2 for CW so I do not believe I need to wire for pin #8.

The voltages coming out of the Viking 2 at the octal socket are correct so this looks to be a good way to go.

Any tips or advice on needed mods will be appreciated.

Thanks, Rich

[DMOD]

Question 1: Is that resister looking component really a choke and what is the rating?

The choke at the bottom of L7 is the L21 choke and is 4.7 uH at approx. 1.0 Amp.

Question 2: What would have caused the component to blow when I attached the VFO and turned on the HV.

Two things. Plate overcurrent and or parasitics.

Since you will most likely be replacing C32 and C46, also located at the bottom of L7, go ahead and replace L21. One can tell of an impending failure of L21 by the black band in the middle.

Do NOT use a choke with a higher current rating because this choke also acts a “last chance” protection fuse for L7.  I used the Murata 11R472C 4.7 uH RF choke available from Mouser as Mouser part number 580-11R472C. I replaced the two caps with 0.047 uF at 2kV for better high frequency response.

On mine, I had to cut the HV wire to the bottom of the choke from the wiring side in order to remove the choke.

I set up a new connection point just above the 6146's with a 2-lug terminal strip and new wire to the choke since the old wire's insulation gets very brittle.

Phil - AC0OB

[WD4DMZ]

Excellent info on the choke. The failure was as you described, it burned thru in the middle. Knowing that Mouser has a replacement part is priceless.

Thanks, Rich

[K9PNP]

You might check the power output octal socket and see if it still has the metal "shield" on it.  Mine did and when you plugged in the VFO power cable, it grounded the HV to the shield; just barely, but it was enough.  Luckily I didn't fry anything important.  Don't know if all the  VII's had this.

[WD4DMZ]

Good input Mitch. When I flipped on the HV switch that is when the sizzling started. Elaborate on the shield. I see nothing from the outside that looks like a shield.

Rich

[Pete, WA2CWA]

You might check the power output octal socket and see if it still has the metal "shield" on it.  Mine did and when you plugged in the VFO power cable, it grounded the HV to the shield; just barely, but it was enough.  Luckily I didn't fry anything important.  Don't know if all the  VII's had this.

What shield? The manual doesn't show any shield.

[WD4DMZ]

Great photo Pete. Saved me the trouble of moving my V2 to the bench to look for a shield.

Rich

[DMOD]

Mine doesn't have a shield either.

BTW, those 6AL5's have been known to develop cathode, filament, and plate shorts, which is why I solid-stated mine with a dropping resistor and caps after the dropping resistor.

The last thing you want during a transmission is to lose bias, resulting in plate current going out of control and burning up L21.

Phil - AC0OB

[K9PNP]

The shield does/did exist, at least on some units.  From 7-15-53 parts list that was with the original manual with my V2:   VFO Socket Shield, Johnson part # 120-277B-1, designated S7 for item #.  It was originally between the chassis and the octal socket used for VFO power.  Don't have a working digital camera or I would add a picture.  Roughly 22 or 24 ga metal, 2.5" diameter with holes for the socket mounting screws and for the octal socket holes.  Still have it in my "stuff removed from V2" box.

Possibly they quit using it later or they have been removed for some reason.  Don't have any idea what happened as far as why it is not there on some and was on others.

[DMOD]

And many of the earlier VII's didn't have a clamp circuit so if your bias goes, so goes your finals, L21 and maybe your meter.

And assuming the clamp circuit IS there, the 6AQ5 clamp tube will only last as long as the glass envelope doesn't melt and implode.

Phil - AC0OB

[w4bfs]

The shield does/did exist, at least on some units.  From 7-15-53 parts list that was with the original manual with my V2:   VFO Socket Shield, Johnson part # 120-277B-1, designated S7 for item #.  It was originally between the chassis and the octal socket used for VFO power.  Don't have a working digital camera or I would add a picture.  Roughly 22 or 24 ga metal, 2.5" diameter with holes for the socket mounting screws and for the octal socket holes.  Still have it in my "stuff removed from V2" box.

Possibly they quit using it later or they have been removed for some reason.  Don't have any idea what happened as far as why it is not there on some and was on others.

I believe the shield was added during production for tvi reduction purposes ...have seen it in some but not all VII .... varnished cambric was used thru the holes to insulate the pass thru ... sometimes it worked its way out where careless lead dress could get you in trouble .... not needed nowadays

[WD4DMZ]

Good discussion. What does the shield look like? I presume it is inside the chassis like a small metal box or shell.

My other question pertained to xtals. Both of my 40 meter xtals run 1kc high in the V2. For instance, the 7290 xmits at 7291. However, my 80 meter xtal has no shift and is dead on 3740. Both 40 meter xtals are exactly on 7290 and 7295 in my DX 60 so I do not believe it is the xtals themselves causing the shift in the V2.

Any idea what coud cause this? I've turned them around in the sockets and moved them apart to different sockets to no avail.

Rich

[DMOD]

Possibly crystal heating.

Replace C14 with a 47 pF, 500V ceramic in series with a 27 ohm carbon composition resistor.

The resistor should be on the crystal side of C14.  

Phil - AC0OB

[w1vtp]

And many of the earlier VII's didn't have a clamp circuit so if your bias goes, so goes your finals, L21 and maybe your meter.

And assuming the clamp circuit IS there, the 6AQ5 clamp tube will only last as long as the glass envelope doesn't melt and implode.

Phil - AC0OB

I'm puzzled about that statement.  I thought the negative bias on the 6146's would guard against excessive final plate current in the event of loss of drive.  I imagine that during CW mode key up modes were somehow an issue with the 6146 screens and hence the clamper circuit.

In the V1 which uses a single 4D32 the screen was more rugged and could stand the key up modes.

I'll be following this with some interest as I have a V2 in the back room that I want to put on the air.

[DMOD]

I should have referenced that to one of my earlier posts:

BTW, those 6AL5's have been known to develop cathode, filament, and plate shorts, which is why I solid-stated mine with a dropping resistor and caps after the dropping resistor.

The last thing you want during a transmission is to lose bias, resulting in plate current going out of control and burning up L21.

And many of the earlier VII's didn't have a clamp circuit so if your bias goes, so goes your finals, L21 and maybe your meter.

And assuming the clamp circuit IS there, the 6AQ5 clamp tube will only last as long as the glass envelope doesn't melt and implode.    

What I was trying to convey was that the lowly 6AL5 tubes have been known to fail at inopportune times, resulting in no bias at all to protect anything.

And many of the early Vee-two's had no Clamp Circuit.

So, if you have an early Viking VII (pre-June 1953) without the clamp circuit and the 6AL5 tube fails, your bias fails to the Modulator grids, the buffer and the finals, and the plate currents soar.

In the later Viking VII's (from about June 1953 on up) and the CDC's, the Clamp Circuit will drop the screen voltage across R28 in an attempt to save the finals and L21, but it can only do that for a limited time.

I also have a Viking I and I have no doubt the 4D32 could withstand a bias failure.

Phil - AC0OB

[WD4DMZ]

Tonight on the 3740 net one AMer suggested adding a small cap in parallel with the xtals. After some trial and error a 10pf cap dropped both of my problem xtals exactly 1kc so I am now spot on.

That was a simple and inexpensive fix.

Rich

[DMOD]

FWIW, those silver mica's have been known to change value and or get leaky, which is why a replacement is often suggested. Due to heat and moisture, those old "postage stamp" mica's can form dendrites from silver oxide migration. A dendrite is a crystal or crystalline mass with a branching, treelike structure, which can cause frequency drift after warm-up, intermittent operation, and noise.


Modern mica's are constructed differently and sealed with expoxy's or other sealants and are very stable within their specified ratings.

http://www.capacitorguide.com/mica-capacitor/

http://amfone.net/Amforum/index.php?topic=4906.0

I can't say I have ever had to "pad" the OSC circuit because crystals were off frequency.

I have had FT-243 crystal that were not ground correctly.

What does this padding do to the 75m crystal frequency?


Phil - AC0OB

[KD6VXI]

I was just talking to W6ZKH this afternoon on his valiant.

He,  also,  had to change every silver mica cap in the output.

Guess it's common.

--Shane
KD6VXI

[WD4DMZ]

Good idea to change out the mica caps. Would it be OK to use ceramic replacements? I have quite a few on hand.

Rich

[DMOD]

Good idea to change out the mica caps. Would it be OK to use ceramic replacements? I have quite a few on hand.

Rich

Yes, I use ceramic caps. with at least 500V ratings.

Phil - AC0OB

[W2JBL]

    I reference to the crystals not oscillating on the desired frequency this is normal. The "ham" and mil surplus FT243 crystals we grew up on were of poor frequency tolerance and even though typically designed to run into a 32PF parallel load capacitance face a myriad of different circuits, load capacities and drive levels. Adding a cap across the crystal is common, and works up to the point the crystal starts to get weak. My father taught me two other ways around the problem, both of which only lower the frequency, but eliminate the need for adding components to the transmitter. Remove the crystal blank from the holder and using a #2 lead pencil draw a dot about 1/4 diameter on each side of the blank. More lead= lower frequency. This is a game of trial and error and also has a point of no return. GENTLY remove the pencil lead with a rubber (non abrasive) eraser to go back, and wash the blank in alcohol or acetone to get back to the starting point. The other trick is to submerge the blank in iodine , remove and let dry. Test the frequency and repeat. This is also a trial and error type deal but sometimes works better than the lead pencil method. Keep the crystal blank and it's plates absolutely free from finger residue, dust etc and use lots of solvent or alcohol to insure all parts are clean before reassembling. NEVER use paint thinner, or any solvent containing oils. Acetone, brake cleaner, carb cleaner all work very well. I prefer 91% isopropal alcohol from my local chain pharmacy store, it's cheap and not as toxic as the other alternatives. Do not use rubbing alcohol- it contains mineral oil.

     A third method involves increasing the spring tension in the holder. If you have a good crystal collection you will notice many different types springs inside the FT243 holder. The springs with heavier wire and fewer turns are stronger. Increasing spring tension will lower the frequency. Decreasing it will raise the frequency until there is not enough tension for the crystal to oscillate.

     And another method to raise the frequency involves putting an inductor in series with the crystal. Use a small slug tuned coil form wound to resonate with say about 100PF in paralell with the coil at the desired frequency and tune it with a grid dip meter to where you need to be. Then put the coil only in series with the grid side of the crystal and tune the slug, which hopefully will get you where you need to go. Use caution with this one because the crystal can stop oscillating and the coil becomes the grid tank for your new "VFO"...
Note thaT these tricks will only move an 80 meter crystal about 1-2 KC before you lose oscillation. On 40 meter crystals you can go a lot farther.