viking II 6146w oscillation

[KB8OSB]

 Hello all. Recently started messing with a v2 I had gotten from my elmer a few years ago. To make a long long (long) story short, it had no finals so I installed a set of jan phillips 6146w's a friend picked up for me at dayton. It makes good power but the plate tuning is funny and it oscillates above the band even with the 122 vfo disconnected. It doesnt seem that the v2 has a neutralization circuit so I dont know if I should add one or just junk the w's and try to find some a's. Thanks in advance for any advice.

[WQ9E]

One of my Viking II transmitters is running W suffix finals and the other has B suffix and both are stable so I doubt if the W suffix tubes are causing your problem.  What is the history on the transmitter, do you know why it was missing its finals?  I suspect it had an issue no matter what finals were in there.

A poor ground from corrosion or loose hardware in the final section is a possible cause of this instability so check all of the grounds in the final area.  I just repaired a Valiant that had apparent low output because of the meter reading far more than the actual current.  In this case it was a factory unit and the metering shunts were fine but the connection point for the shunt ground was a riveted connection which had developed some resistance. 

Examine L-6 and L-7 carefully for any signs of damage, I have run into unusual tuning issues in rigs where a choke was damaged due to previous flashover.  Are the final screen bypass caps in good condition?

Make sure the clamper tube circuit is adjusted properly and then pull V5 to determine whether the problem is with the final or earlier in the RF chain.

Hundreds of Viking IIs are still in use and it should operate normally without the need for added circuitry once you identify and correct whatever is causing the current issue. 

[KB8OSB]

Well I checked all that stuff. The finals were missing bc my elmer only had one set of tubes to share on several pieces of equipment hihi. So anyway when I pulled v5, it stopped. No buffer, grid, plate or oscillator indication which is what I'd expect. So I guess this means the trouble is in the oscillator? I never really knew a terribly great deal about boat anchors even though they were my main rigs for years. Something blows up, find the short. When it got goofy, off to Mike's house we go

[WQ9E]

Sounds like the trouble is in the exciter chain, one of the tubes must be taking off on its on.  I can't remember if there are supposed to be shields on those tubes (V5 and V6)  but check for missing shields, the manual and photos should show whether they have shields.  Also check the bias voltage, a bad filter cap in the bias supply creates lots of issues.

You could try plugging V5 back in and pulling V6, this MAY help you narrow it down to a single stage.

[KB8OSB]

Ya know, as I check and recheck things, the clamper circuit doesnt seem to be working. R30 fully clockwise the plate current is 100ma. Dont think that has anything to do with it but I'll swap in another 6aq5 in the morning. Everything is too hot to touch. Thanks fer ur advice om. I'll see if I can get the clamper working and move on along...

[ke7trp]

For what its worth, My johnson transmitters are not happy with W tubes. The rig was intended to use regular RCA 6146s made in the 50s. You might get away with it on some bands and or brands of W tubes but on my radios, as you go up in Frequency the rig will oscilate and take off. The funny thing about is is the driver current is what is taking off and not the plate current. 

Here is an article explaining some differences and it includes why some have used W's and some have had trouble like myself.

http://www.members.tripod.com/NRWILLIAMSON/t6146.txt


I hate to see you spend time messing about in the rig only to find that a simple swap to the old 6146 calms everything down.  I just watched a local do this for TWO weeks as his rig kept oscilating and taking out 100 KC of the band. After every possible thing was changed and altered, He took his prized W rugged tube out and put a 6146 back in and it was fixed.

[Pete, WA2CWA]

My Viking II uses "B's". So does my Apache, Ranger, and Valiant. I've never seen the issue Glen describes in your link.

[ke7trp]

The rigs work best with the old RCA black plate 6146 with date codes in the 50s.   Thats what it was supposed to have.  I have a large supply of 6146s and the highest output is the amprex.  So if you want the most power, Get them.  They output more then any other tube I have tried.

As far as stability,  Get the old RCA tubes and be done with it.  Otherwise, They oscilate like crazy on on the higher bands.


C

[Pete, WA2CWA]

Of course, back in the mid 50's, they didn't have "B's" or "W's". 6146B's, Sylvania/ECG-Philips‎, are used in my Viking II. GE, 6146B's, are used in my Apache. Two 6146B's, RCA, and one 6146B, GE, are used in the Valiant Final. I think I have 6146A's in the modulator.

Doing the strut, my B's are better then your W's. 

[ke7trp]

Thats interesting.  I tested them all in my ranger 1, I found the old RCA to be the best and most stable on higher bands. At least in the ranger that was the case. The W's should not be used but thats just my experience.

C

[KB8OSB]

Ya it was kind of a case of mistaken identity. I wanted the a's, my friend said the w's were the same. Then I start finding out they're not the same. I wish someone local had a couple a's that would trade for some nos w's. But the rig hadn't been used in a long time and may have a legitimate problem. If I pull v5 everything stops so I guess that rules out the finals. 

[Pete, WA2CWA]

Try a different V5 (6AQ5). In a pinch, switch the clamp tube with  V5. They are both 6AQ5's.

[KD0HUX]

 I had the same problem with the Valiant . I was told 2 ditch the 6146w and run 6146 or the 6146a.  I put the 6146w in the mod section no problem

[Jim, W5JO]

Does anyone neutralize the finals when they change tubes in the Valiant, even the revered A models?  You should, you might be suprised.

[KM1H]

The W originally came out in the mid to late 50's as a military and rugged version of the regular 6146.

The W is not a B variant unless it is date coded after the B was released which was around 63-64.

The A is simply a 6146 with RCA's "Dark Heater" controlled filament for varying voltages in mobile service. It otherwise is a direct replacement.

Since a properly operating V-II can use any 6146, just dont mix them up without knowing what youre using. I cant say what happens when you try European or Japanese variations but I do know the 6146B works fine in Kenwood hybrids that came with S2001's. Ive also rewired the sockets and used the much cheaper 6883B's.

Of course the V-II has to be working properly and not have the bias rectifier or its filter cap dead which will guarantee a runaway condition as will a leaky .1 paper cap at the clamp tube grid.

Carl

[WA1GFZ]

check your bias voltages if all the tubes run hot.

[ke7trp]

Update:

Local tuned his Ranger 2 up to 15 meters and found oscilation and Driver current pegging out. 

He spent some time replacing the rivits in the tube socket with bolts and added straps.   No change. Internet said this is a common problem.

I found the 15K resistor was missing on the choke.  No idea why. Put it back as per schematic, no change.

I suggested he try a standard 6146 and asked what was in the radio,  You guessed it, 6146W.  He swapped the tube, the osc stopped and the radio is rock solid on 15 meters again. 

The radio ran perfect for years on 160, 80 and 40 with the W tube.

Thought I would throw that out there.  The Ranger 2 is not happy with the W tube on the 15. What was bad about this was this ranger drove the Desk KW so that little osclation turned into a BIG ONE

C