The Viking Saga Begins...

[N8UH]

Hello to all! First off, I just wanted to introduce myself. I'm new to posting on this site, but have been monitoring for a while. Today, I received my newest project: A Viking II. But first a little about me.

I've been a Ham for a little while now (about 20 years), and started out with an old Tempo One. Worked on it, got it on the air, loved it. I worked CW and SSB. Later got a more modern rig. One day I was tuning around on 75 and ran across a net, and figured I'd join in. They came back and told me I needed to switch over to AM (that was a bit embarrassing) 
I joined in on AM, but my PW signal was a bit hard to copy I understand... But I always remembered that time!

Fast forward a bit.

Now, living in an area that isn't exactly Ham-Friendly, and with nothing but an 857d as my all mode rig (I have a couple of Elecrafts I built, but QRP CW/SSB only). Portable QRP CW is the order of the day. At hope while tuning around every now and then, I longingly listen to the wonderful sounds coming through my headphones on 3870. The bug bit me, and at the same time, I found myself longing for some good 'ole heavy iron and glass.

So, enter the Viking II.

The things a beast, but in need of TLC. Some of the wafer switches are corroded. Most tube sockets are corroded. The 6146Bs had HOLES MELTED THROUGH THEM (That's a new one for me!) It seems like time, abuse, and neglect have taken their toll on this poor hunk 'o iron. At least the undersides look pretty clean.

There was an older audio mod done to it. I found a couple additional pages tucked in the manual and it appears to be the "W6ZLW Revamped audio circuit for viking transmitters" There was a 6ba6 in place for V6. V1 and V2 have been replaced with a 12??? and 12AU7 respectively (according to the schematics, it should be a 12ax7 and 12bh7). Not sure how well this mod performs compared to the ones over on AM Window, but there you are. I see a rework in it's future? 

Then, there is some kind of keyer mod. There is also a schematic. It consists of a box mounted above the crystal holder, containing a 5814, and another box (Seems to be related) located above L1, that has a 6AH6, and a BNC jack...    Then there is a 3-conductor wire coming out of that box, that goes to a terminal strip near the 8-pin socket on the back. It's going to take some detective work to figure that out...

SOoooo anyway, it's going to need some work. No problems with that, I'm up to it (I hope!). This will be my first full BA restoration. I've repaired a few, but this one needs more. Obviously, it's going to need new caps. While I'm in there, I'll probably do the resistors too. Not quite sure what to do with the audio and keyer mods.

So, in addition to my long ramblings above, some specific questions:

• What is a good way of cleaning the oxidation off the tube socket and wafer switch contacts, is there some sort of solvent I should be using, or just go after it with a bit of emery cloth?
• L7 is looking a bit ragged. If it should need replacement, where might I go?
• Seeing that this beast was probably misused a bit (understatement) what should I be looking at as possible weak/failure points?
• While I have everything out, is there a safe way I can give the chassis a bath? There is years of dust/grime in there.
• What other things would you all recommend I attack/check/mod while I'm tearing down and building back up?

I'm not looking for a concourse restoration here. I'm looking to have a clean, reliable, good sounding rig. I'd like to stick to 50's tech though. I'm just traditional there I guess. I guess I'm looking for the top picks for this rig to make it shine.

My hopes are to get this beast running again, pair it up with a suitable BA receiver, and finally try and make my way into the AM groups here out west. Then I can be making those beautiful sounds (albeit with a bit less power).

Sorry about the long-winded ramble, and thanks for everyone's contributions to this wonderful site, it's an inspiration!

73

-Tim

[w4bfs]

welcome to the group, Tim .... you will find a wealth of knowledge here ... I like messing around with Vikings ... got one V1 and 3 V2's ....all of them are experimental test beds since they were VERY hammy hamboned when i got them

1. The fil / lv transformer power supply can benefit by considering that nominal line voltage has been raised from 110V to 120V across most of the US.  If you are going to solid state the rectifier, use the low current 5V winding to buck the primary and add a 1A fuse to it as well.  This will help keep it healthy.   Since the solid stated output voltage will be higher, consider moving the filter cap(s) to the load side.  I used a .5Ufd on the input and a 47Ufd on the output.  This yielded close to +275V here.  Don't leave off all capacity on the input because of back emf from the inductor on shut down.

2. The hv ps solid stating will yield considerably higher voltage (800V +) and will stress the bleeder resistor.  I didn't like the stock arrangement and replaced the hv xfmr in all of them.

3.  corrosion control .... be careful what you use .... tarnished silver is no problem and better left alone ... WD40 is your friend here (other stuff is good) ....

be sure to do searches on these subjects 'cause most of them have been dealt with before, much more thoroughly than I have done here ... have fun !    73    John

[Superhet66]

Welcome Tim, I'm green here also.

You mentioned emery as a possible contact & socket cleaner.
My only comment is that emery will remove material you may want preserved.  
Also, the [emery] residue left behind will imbed itself & is conductive.

                                                                   DJ

[Pete, WA2CWA]

This has also been recently discussed in another topic and you can find a pair of the old GE 6146W (NOS) tubes online which are exactly the same as the old RCA 6146A tubes. RF Parts has them or Nebraska surplus.

If you're going to recommend 6146W's as a direct equivalent to the 6146A's, you need to get 6146W's that were manufactured before 1964. 6146W's manufactured after 1964 (6146B was introduced into the market summer of 1964) are probably more electrically equivalent to the 6146B's except they have a lower plate dissipation and are classified as being "more rugged", "heavy duty", "one size fits all". I've used 6146B's in my Viking II, Ranger, Valiant, Apache, and several other rigs without the transmitter burping it back at me. However, it's always wise to check and/or perform neutralization when you install any new transmitting tubes such as the 6146 series.

[WQ9E]

The Viking 2 is fine with the different 6146 variants.  It's that high quality stuff from Cedar Rapids that is so picky about its finals   

I have run B and W suffix versions in many pieces of Johnson and Heathkit gear with nary a problem but I will be careful to use the original iteration in my 32S-3 and KWM-2 when they need replacing.  I believe there is a posted update to the Collins neutralizing circuitry to allow later versions to be accommodated.

[N8UH]

Thanks for the great info so far guys!

As for the finals, I've seen on this site many others using A's B's and W's without too much problem. I guess it's a matter of picking a pair and running with them after adjustments are made. I guess I'll keep looking to see what is the best set to use in there without breaking the bank. At any rate, I would assume (we all know what happens there) that the previous owner melted the finals due to negligence and/or  misuse. But that stage is going to be a bit in the future!

As for other comments, I plan on keeping the VT Rectifiers in place, but I had wondered about the elevated line voltages. Is that going to be a big problem if I stick with VT Rectifiers?

Right now, I need to get the chassis clean and get the corrosion out of the tube sockets, get some of the shafts/switches/pots turning again. I'll try out WD40, that sounds like a good plan as far as attacking the corrosion.

Then, I'll be figuring out what, if anything, has catastrophically failed.

I'm probably going to gut the audio/modulator section and rebuild it. My biggest question there is whether or not to keep the original mod in place or perform a new mod. Looking at the schematic, there is a 12AX7 with one half serving as the input, and the other half feeding a 12BH7 connected in parallel going to the mod transformer. It seems like a solid mod, but perhaps I should scan and put this up for the gurus here to see, as I have never seen this mod before. Obviously, I have 2 9-pin sockets to work with here, so I want to make the most of them. At any rate, I can cut everything out, get a couple new sockets and start fresh once I get this figured out.

Thanks!

[W7POW]

Tim,
Welcome aboard!  I am new on this forum as well but have already found the folks here friendly and very helpful.

Only a month ago I too was really wanting to get involved in AM and spent many mornings and evenings listening in here on 3870 in the Pac NW.  I started looking for a decent station and got a little lucky.  While listening to a local swap net I heard (from the next room) the words Viking II and ran into the bedroom to hear a local ham offering it for best offer.  I contacted him and ended up getting the Viking and matching VFO for 100 bucks!  Great deal, right?

Well a week later he calls me and asks if I wanted the old reciever too.  It ends up being a National NC-183 in sad condition but complete.  Needless to say I hauled it home and began rebuilding both the Viker and the NC-183 immediatley.

It has been a fun couple of weeks replacing load of caps and at least a dozen out of spec resistors in both rigs.  I also had to undo quite a few hammy hambone mods in the Viking and troubleshoot some shorts and wiring issues with the NC-183.  Other than waiting on some replacement tubes for the National I am about ready to put these bad boys on the air.  The viking seems to work great into a dummy load but I just have to figure out a antenna and then I will be in buisness.


My Viker is using 6146B tubes and seems to work just fine. 

We would really like to see some photos of your Viking and the condition it is in now.

Good luck and keep us posted.  I look forward to working you on the air.

73,
KF7EOO

[Steve - WB3HUZ]

The 12AX7 - 12BH7 mod sounds like a good one. I'd stick with it. Not unless you do something much more radical will you get improved performance (assuming the mod was executed correctly in the first place). Other has done similar mods.

http://www.amwindow.org/tech/htm/viking2.htm

Thanks for the great info so far guys!

As for the finals, I've seen on this site many others using A's B's and W's without too much problem. I guess it's a matter of picking a pair and running with them after adjustments are made. I guess I'll keep looking to see what is the best set to use in there without breaking the bank. At any rate, I would assume (we all know what happens there) that the previous owner melted the finals due to negligence and/or  misuse. But that stage is going to be a bit in the future!

As for other comments, I plan on keeping the VT Rectifiers in place, but I had wondered about the elevated line voltages. Is that going to be a big problem if I stick with VT Rectifiers?

Right now, I need to get the chassis clean and get the corrosion out of the tube sockets, get some of the shafts/switches/pots turning again. I'll try out WD40, that sounds like a good plan as far as attacking the corrosion.

Then, I'll be figuring out what, if anything, has catastrophically failed.

I'm probably going to gut the audio/modulator section and rebuild it. My biggest question there is whether or not to keep the original mod in place or perform a new mod. Looking at the schematic, there is a 12AX7 with one half serving as the input, and the other half feeding a 12BH7 connected in parallel going to the mod transformer. It seems like a solid mod, but perhaps I should scan and put this up for the gurus here to see, as I have never seen this mod before. Obviously, I have 2 9-pin sockets to work with here, so I want to make the most of them. At any rate, I can cut everything out, get a couple new sockets and start fresh once I get this figured out.

Thanks!

[N8UH]

Great stuff guys. Much appreciated! I went ahead and took a photo of the schematic. The scanner is still packed away, so sorry about the quality. Perhaps the gurus here could take a look at it. Looking at this one and comparing it to the one over at AMWindow, there are some differences in the coupling caps, input coupling, etc. I'm wondering if a hybrid approach is in order here... hmmm.

Also attached, for your viewing pleasure is a pic of the finals. I'm putting these up on a shelf...

[w3jn]

Wow, the corner frequency on that amp chain is pretty hnyellowey, about 800 hz at the lower  (1/(.005E-06 * 250K)).  250K because you have the 470K plate and grid circuits in AC parallel.  .05 (or .047) coupling caps would give you an 80 hz corner freq.  If the driver tranny is stock you may not wanna go that low, I'm not sure how that driver tranny might act at low audio freqs.

[Steve - WB3HUZ]

I agree with JN. The basic design looks good. The parallel 12BH7 should drive the 807s quite well with a good driver transformer (more on this later). If you want any low frequency response, enlarge the coupling cap between the two 12AX7 stages to at least 0.01 uF.. Same goes for the next coupling cap going to the 12BH7. Then you'll need to increase the size of those decoupling caps (0.25 uF) to something like 10-20 uF. The bypass cap on the 560 Ohm cathode resistor of the 12BH7 is probably big enough but I'd put a new one in there anyway. If you go to 20 or 50 uF, it won’t hurt anything.

The stock driver transformer is the weak link in the Viking audio chain. If you can find a good replacement (Hammond used to sell a great replacement), change it out.

If I wanted to be picky, I don't really like how the first 12AX7 stage is set up. Some cathode resistance would reduce the stage gain a little but would also reduce distortion. This may not matter much, especially if you aren't going for super hi-fi sound.

Good luck. The Viking is a good rig and it is easy to work on. Have fun.

[w3jn]

Those plate decoupling caps I see now are .25, I originally didn't see the decimal point    Indeed, they need to be bigger to effectively provide low impedance decoupling for low frequencies.

[Steve - WB3HUZ]

Yep, lots of lows lost their and maybe motorboat city when the coupling caps are increased.

[WA1GFZ]

Why not eliminate the driver transformer and drive each 807 grid with a triode section as a cathode follower. Then go back a stage and use a triode section as a phase splitter. 6146 on the left may have too much air in it.

[N8UH]

Why not eliminate the driver transformer and drive each 807 grid with a triode section as a cathode follower. Then go back a stage and use a triode section as a phase splitter. 6146 on the left may have too much air in it.

Yes, perhaps just a bit too much air in that 6146 

The phase splitter/cathode follower idea is interesting. I realize that the stock transformer is a little bit on the flakey side, and was thinking about replacing it with a 124E. But, I like the simplicity of eliminating it all together, and I would assume that I would be able to squeeze better audio out to boot.

Does anyone have a schematic or reference I could peek at for a phase splitter/cathode follower design feeding the 807s?

-Tim

[N8UH]

As for the finals, I've seen on this site many others using A's B's and W's without too much problem. I guess it's a matter of picking a pair and running with them after adjustments are made. I guess I'll keep looking to see what is the best set to use in there without breaking the bank. At any rate, I would assume (we all know what happens there) that the previous owner melted the finals due to negligence and/or  misuse. But that stage is going to be a bit in the future!

What it is, is that you can’t use "A" or the correct "W" tubes in the place of "B" tubes when the unit was designed for "B" tubes. You can however occasionally go the other way, using "B'" tubes in place of "A" tubes, but I don’t recommend it for the old Johnson gear. The reason, the "B" tubes have more plate dissipation, more current. If you consider how old those transmitters are and how delicate many of the plate transformers are due to their age it’s not really a good idea.

Just be careful because there has been much confusion over this subject thru the years and you will find incorrect info all over the web. Just because their website says the tubes they sell are the same as “B” tube doesn’t necessarily mean that info is correct.

Anyway, welcome to the fourm…

73’s

Brian

Thanks for the clarification Brian. I see what you're saying there. I guess I'll keep my eyes open for some A's and stick with the original design spec. Thanks!

[WD8BIL]

If I wanted to be picky, I don't really like how the first 12AX7 stage is set up. Some cathode resistance would reduce the stage gain a little but would also reduce distortion. This may not matter much, especially if you aren't going for super hi-fi sound.

I agree. 2 stages of 12AX7 will give plenty of gain. In fact, you may find the gain pot a bit touchy with all the gain. I'd definately go for the lower distortion on the first stage.

[Pete, WA2CWA]

This has also been recently discussed in another topic and you can find a pair of the old GE 6146W (NOS) tubes online which are exactly the same as the old RCA 6146A tubes. RF Parts has them or Nebraska surplus.

If you're going to recommend 6146W's as a direct equivalent to the 6146A's, you need to get 6146W's that were manufactured before 1964. 6146W's manufactured after 1964 (6146B was introduced into the market summer of 1964) are probably more electrically equivalent to the 6146B's except they have a lower plate dissipation and are classified as being "more rugged", "heavy duty", "one size fits all". I've used 6146B's in my Viking II, Ranger, Valiant, Apache, and several other rigs without the transmitter burping it back at me. However, it's always wise to check and/or perform neutralization when you install any new transmitting tubes such as the 6146 series.

No.., the GE "W" tubes are different than the other "W" tubes made after 64. The GE's made after 64 are still like the old "A" tubes. That's why when people make the mistake of using them in the Kenwood transceivers they smoke the resistors

There are also one or two more "W" brands that are also the same as the "A" tubes, but I cant remember which ones. The 6146W Sylvania / ECG-Philips are the ones just like the "B" tubes another JAN tube is like the "B" tube too.

Also, from RF Part's website is the below statement. (These were made post 1964)

"6146W-GE  (GE Brand) is not recommended for Kenwood transceivers, and is not interchangable with the 6146B."

http://www.rfparts.com/tubetran.html


P.S. Some vintage gear designed for the old "A" will accept the "B" tubes without much trouble or modification, but they are still not exactly 100% compatible without doing anything at all. If it was designed for the old RCA “A” tubes then its better use “A” tubes or the equivalent “W” tubes. The GE tubes that RF Parts sells should be the same as the ones Nebraska advertises, but Nebraska has the wrong description on their website. They state “In most cases, our 6146W will directly replace 6146, 6146A and 6146B.” That is incorrect information.

All 6146W specs (GE, JAN GE, RCA, ECG, Philips, etc.) I've seen have one common characteristic that makes them compatible with the 6146/6146A series. They all have a lower plate dissipation then the 6146B by about 5 to 7 watts per tube. The major difference lies in the inter-electrode capacitance values between the 6146/A/B/W tubes. "W's" manufactured before 1964 were made to have identical (within tolerance) inter-electrode capacitance values with the 6146/6146A's. Substitution was generally seamless requiring little or no additional neutralization when operated on high frequencies. "W's manufactured after 1964 (I believe GE started their manufacture sometime 1965), the physical design of the internal tube structure was designed using the 6146B model so that inter-electrode capacitance would be identical (within tolerance) between both tubes. The GE specs I have seem to confirm that their "W" and "B" were the same. However, there were a number of industrial (4 digit tube numbers) versions of the 6146 family so it's possible there exists an industrial equivalent of the "W" that matches the internal specs of the 6146/6146A that were made well after the transition to only making 6146B types.

As to Kenwood transceivers (the hybrid series), many burnt, cracked, and open cathode resistors, and along with possible burnt PC boards, were also prevalent using the original tubes S-2001A's which are equivalent to the 6146B's. Besides their CB popularity in the 70's and 80's, the hybrids were quite popular with the contest crowd so many of them took quite a beating over the years. Although Kenwood documented the dip and load tune up procedure in their manuals, they also said you could just turn the meter switch to read RF output and tune all the controls for maximum output. The dip and load procedure did specify to keep plate current below some fixed value but in the "tune of maximum output" most probably didn't realize the ramification of not monitoring plate current. If you tune most of those rigs just for maximum RF output, plate current could easily hit the 300 ma mark which is well beyond what the 6146B's can handle. Substituting 6146W's in place of the "B's" can further exacerbate the problem because their plate dissipation is even lower then the original "B's". Even today, if you substitute any 6146B with a 6146W, you need to be aware that the "W's" plate dissipation is lower and your tune up procedure needs to take that into consideration. Example, if your tune up procedure using 6146B's says to tune for a maximum of 225 ma plate current, with the "W's" you should probably adjust it to something around a maximum of 200 ma. With the Kenwoods, this would keep the life of the cathode resistors in much safer territory.

[ke7trp]

If it helps.  I swapped in about 5 different 6146s into my ranger. The W's I had would not work. The GE had low output and funny tuning curve. Major oscilation. They worked fine in the TV7.  The hands down best tube was an old Amperex 6146.  It made more power flat out.  My Valiants def like old RCA 6146s. 

C

[N8UH]

The 6146's seem to be a hot topic here (Bad pun, I know). But it seems that it's just best to find some NOS 6146's and call it a day. However, I'm open to doing some mods if I can use a more common variety...

I got to work on the Viking today and find out more. All the transformers seem to check out. R13, the bleeder resistor, is open (big surprise).  As for R13, I think I'll take this approach: http://members.cox.net/n4jk/viking_ii.htm and use a couple of 0A2s to give me regulated screen voltage to the 807s, with the added bonus of more tubes (I'm sick, I know it.)

Which leaves me with the audio/modulator section. I like the idea of the phase splitter/cathode follower to eliminate the driver transformer. I'm still a little foggy on the circuit though. The best I could find here is the KI5SG drawing.

Any input?

Thanks!

[WQ9E]

NO mods are necessary to use 6146W or B variants in the Viking 2.  My V-2 has been running a set of 6146W tubes (from Fair Radio) for the last 10 years.  Find a good pair of 6146 (plain, A, B, or W or 6293) and plug them in.  The set of tubes in there was killed by stupid abuse by the previous owner-the only tubes he couldn't have melted would be those with open heaters

One addition to Pete's excellent earlier comment about not loading rigs to too much plate current: with most of the older sweep tube rigs you do need to carefully and QUICKLY load to the rated plate current and then reduce power to a more sensible level via the drive control.  Otherwise the screen current will soar (due to light loading) and the screen is easily damaged in most of these tetrode tubes.  This is also true of 6146 based rigs but the screen is a bit more robust than that of many of the TV horizontal sweep tubes pressed into RF service. 

Do watch the control grid current with your class C 6146 finals, 3 mils per tube is the max to avoid degrading the control grid.  Johnson advised 5 mils per tube in their earlier manuals but due to many warranty failures (making RCA most unhappy) an addendum was added to the early manuals reflecting the proper current.

[WB4AIO]

I like the idea of the phase splitter/cathode follower to eliminate the driver transformer. I'm still a little foggy on the circuit though. The best I could find here is the KI5SG drawing.

Any input?

Thanks!

My issue and notes were stolen so I don't have it anymore, but if anyone here can find Alternative Modulation, Issue No. 6, November 1983, my article "Viking Valiant Modifications" details a phase-splitter and resistively coupled driver for a pair of 6550s, with negative feedback around the whole thing, that I built into a Valiant and would be pretty easy to adapt to a Viking, even using the 807s if desired.

This schematic of a guitar power amplifier uses a fairly similar transformerless driver circuit

http://www.drtube.com/schematics/ampeg/vt40pwr-jp.gif

and it comes from this interesting collection of tube amplifier schematics:

http://www.drtube.com/guitamp.htm


With all good wishes,


Kevin, WB4AIO.

[WD8BIL]

Check this one out too.

http://www.amwindow.org/tech/htm/valiant/audio.htm

[N8UH]

Ahhhhh! I think this is starting to come together in my mind. It looks like I could adapt the front end from Viking mod over at AM Window, the phase splitter from Kevin's link (great site BTW, THANKS!), and take a little bit of the KI5SG for driving the 807's and a sprinkle Valiant mod to get the 120% Pos. mod peaks and negative feedback. WHEW! Sounds like a recipe...

I guess I'll study all of these to come up with a hybrid approach on paper, and run it by the folks here. This will be interesting!

Thanks again for all the great comments and suggestions! 

-Tim

[N8UH]

Okay! Let's see how this works. I combined everything in what I hope is the right way. The big question marks are the coupling and bypass caps. Also, I would like to configure the input for a low-Z dynamic mic, so some massaging is in order there I'm sure.

What do you guys think?