Viking II capacitor question

[KB3RJH]

I am somewhat new to electronics and older tube equipment and was wondering which of the Capacitors to replace within this unit. I can solder and whatnot so that's not an issue. I have been told a few times that the electrolytic caps need to be removed and replaced but, they look so clean!?! Does it not matter how nice they look? I mean, I pulled the bottom cover off of it and I was amazed at how clean the unit was from sitting for 15+ years in my dads house. I know he never used it and the receiver (NC 183d) works great! Now, I do have to replace the power cord and the coax chassis connectors on the viking because they were totally dry rotted but, not sure what else I should/shouldn't replace on this. I took advice from another ham (sorry, it's been a while) to pick up a variac to make sure it doesn't get too much voltage when I first turn it on but what would be the problem with starting it up if I don't replace those caps beforehand. Sorry for the silly questions but, I'd rather be prepared than go into this blindly. I do have the schematics for it as well...

Anthony
KB3RJH

[WQ9E]

Anthony,

The electrolytics in the B+ and the bias supply should be replaced; fortunately the Viking 2 uses an oil filled capacitor for the HV and it should be fine.  If you don't replace the capacitors in the B+ supply the possible results are (from mild to major) extra hum, reduced performance, additional load on the supply from leakage, and catastrophic failure could damage the rectifier, transformer, and choke.  If the bias caps lose capacity then then you are going to lose bias voltage and cause greatly increased draw from the plate supply leading to lots of damage.  You also have some small electrolytic caps used as cathode bypasses in the audio stages and reduced capacity here will cause reduced audio gain; particularly at lower audio frequencies.  So the short answer is, replace the electrolytics!

I would also replace any wax/paper type caps you find just to avoid later troubleshooting issues.  Any disc ceramic and mica caps should be assumed good until you find out otherwise.

If your unit still has the original 2 fuse plug it is potentially dangerous.  If you are very careful always to keep a good ground connected to the case AND if you mark the neutral side of the plug (make sure your outlet is correctly wired) and also put the proper 5 amp fuse in the "hot" side of the plug and a 20 amp fuse in the neutral side it will be OK.  It is probably better to just replace the cord with a modern 3 wire and use an inline fuse holder to install a fuse so you won't need to add any holes into the transmitter.

A potential problem area is with the bases/sockets of the 5R4 rectifiers getting dirty and creating carbon tracks so be sure and clean the sockets and tube bases before use to avoid this problem.

These are all really pretty minor things to do and the Viking 2 is a rugged and reliable transmitter, enjoy it!

73, Rodger WQ9E
 

[KB3RJH]

Thanks, that's the best reply I have gotten so far since I've had this monster. My only other question would be is... is there any other test equipment that I should have other than just a digital volt meter. I have a cheesy radio shack one but it seems to work fine for the computer work that I have to use it for from time to time (ie: checking outlet voltages and whatnot). I see that a lot of hams have oscilloscopes and signal generators and other odds and ends in their shacks. I'm sure that they're helpful but, want to make sure that I have everything I should before digging too much deeper into this behemoth.

Anthony

[WQ9E]

Anthony,

Your DVM should serve you well for now.  There are times when oscilloscopes, signal generators, and frequency counters can really make troubleshooting and alignment easier but for now your meter and a decently calibrated receiver should work fine.  But if you catch the collecting disease like the rest of us then more test equipment is definitely in your future!

For now the most important thing is to play it safe.  The Viking 2 has lethal voltages at many exposed points both above and below chassis.  The oil filled capacitor can hold a lethal charge for months if the bleeder resistor fails.  This is not to scare you but just to make sure you stay around long enough to add a lot more vintage gear

For now, don't do any troubleshooting inside the case with the Viking 2 plugged in.  Remove all rings, jewelry, etc. when working on the gear and when making any live measurements in the future keep one hand in your pocket.  Wear well insulated shoes when working on the gear.  Get in the habit of shorting the plate and B+ supplies to ground with an insulated handle screwdriver before doing anything inside the unit.  Always feel free to ask others if you have questions, those who have gone before you are glad to help!

73, Rodger WQ9E

[w4bfs]

Rodger is absoutely correct !!  ...  be careful and enjoy the results of yer werk ... let us know if you need parts ... 73  ... John

[WA1GFZ]

Look for date codes on the power supply caps. They may have been changed. I would replace them if they are wax coated. Chance out any wax caps in the audio section. Two V2s in a row had leaky cap feeding the audio level pot. This saturates the driver tube making audio sound nasty.

[KB3RJH]

Great! I'll keep that in mind for sure. Just want to get all my ducks in a row before I get into a high voltage transmitter like this. I picked up a 6' 3 wire power cord for it since the original one was completely dry-rotted and some SO-239 chassis connectors since they were the old ceramic types and were completely stuck to the pl-259's that came with the unit. My dad gave it to me about 6 months ago, he bought it and a NC 183d from a SK estate sale in Frederick, MD over 15 years ago and never did much with them. He listened to the receiver a few times but he wasn't a licensed ham so he couldn't do anything with the transmitter and it sat in his living room for all those years waiting for someone to pay attention to it again. ;p Hopefully I can do right by it and bring it back to life again! I'll for sure have to scream "It's alive" like Gene Wilder (Dr. Frankenstein) when it is finally ready to go, he he.

[WQ9E]

Sounds like you have a good plan!  The Viking 2 and NC-183D make a very nice vintage pair.  The next time you have the bottom off of the NC-183D take a look and make sure there isn't a .1 capacitor connected from either pin 4 or 6 of the 5U4G rectifier to ground.  National used these on the HRO-60 and sporadically on some of the other receivers of the era; my NC-183D, HRO-60, and HRO-50T1 all came with one.  If it shorts then it takes out the power transformer and this has happened to a fair number of HRO-60's and 183D's.  The capacitor really doesn't serve any useful function and I think it was later dropped from production so I would not bother replacing it with a better modern one.  I imagine if Carl KM1H comes across this he may be able to shed a bit more light on this capacitor since he is our "National Alum" and a great source of National knowledge.

Rodger WQ9E

[Jim, W5JO]

Sounds like you have a good plan!  The Viking 2 and NC-183D make a very nice vintage pair.  The next time you have the bottom off of the NC-183D take a look and make sure there isn't a .1 capacitor connected from either pin 4 or 6 of the 5U4G rectifier to ground.  National used these on the HRO-60 and sporadically on some of the other receivers of the era; my NC-183D, HRO-60, and HRO-50T1 all came with one.  If it shorts then it takes out the power transformer and this has happened to a fair number of HRO-60's and 183D's.  The capacitor really doesn't serve any useful function and I think it was later dropped from production so I would not bother replacing it with a better modern one.  I imagine if Carl KM1H comes across this he may be able to shed a bit more light on this capacitor since he is our "National Alum" and a great source of National knowledge.

Rodger WQ9E

I am about to send a bad NC 183D transformer to Gary/WZ1M for rewind.  These radios generate a lot of heat even when they work right.  It is also imperative to check that filter electrolytic for leakage.  If it does not meet specs, replace it.  In fact since this radio hasn't been used much in the past 15 years, I would replace it anyway.  You can get a 40-20-20 @ 450 volts which will fit right in for abou 25 dollars from Antique Electronic Supply.

I hope you got the manual with it.  There are two different versions of this radio I have seen.  One uses a 6J5 as a phase inverter for the audio section and the other uses a 6SN7.    You will also find a great number of resistors that will be high in value and since there isn't that many in it, just replace them while you are there. 

Another thing that goes is the screen by-pass caps.  Replace them, they are paper and tend to short at their age.  One big word of caution.  The tube pins are most fragile.  They will break if you put very much stress on them, so work with them carefully.  The tube sockets are rivited in place so replacement of the socket is quite a chore.  If you should break a pin, try just replacing that pin.  It can be done but it isn't easy.  This is true of both the Octal and minature socket pins.

Once everything is done, check the voltages and get them right.  By doing that, you will reduce the heat generated.  I had to replace an IF can because the heat had warped the cardboard form so much the slug separated from the adjustment screw.  It is a great receiver when it works right and sounds very good.

[WA1GFZ]

I use solder wick on tube pins then snip the cap wire rather than trying to unfold it from the socket pin. This puts a lot less stress on the old pins. Usually I just have to spread the last fold of the wire to free it. Sometimes you can snip the middle of the fold if you are lucky.

[KB3RJH]

WJ5O, I actually downloaded the manuals for the both of them with schematics from BAMA I believe. I haven't really noticed that the 183d gets hot. Doesn't seem to anyway. I'll check to see what phase inverter is in it... It should be good fun to get the pair in better condition than they are at the moment. It looks like I have a great deal of work ahead of me... Gonna print out these suggestions. Thanks for all the replies!

 

[N3DRB The Derb]

teh stock 6AU6 speech amp and driver tubes can be replaced with 6AH6 pin for pin but the AH6's have more gain. gives you about 2 more 'numbers' on the mike gain control for any given outpoot.

[W3NP]

One more tip concerning the Viking II. The rotary inductor in the final plate circuit should be very carefully cleaned with air, a brush and then perhaps some isopropyl alcohol. After this, run the wheel back and forth on the coil 6 or 7 times - the more the merrier.

Also, check that there is sufficient tension on the wheel that rides the coil.

Do this BEFORE using the xmtr for the first time. Do not spray any contact cleaner or lubes on this assembly. Once arcing occurs on the rod that the wheel rides on, on the wheel itself, and on the coil, it is very difficult, if not impossible to remedy and will continue to get worse as the contact surfaces get burnt. It will arc and spark as you tune the final and will always be flaky - usable but annoying.  I learned this the hard way about 30 years ago.

[KB3RJH]

Just a small update and a question...

Well, got the new power cord installed on the VII last night so that should be good to go, not putting the other end on till I get the caps replaced. Was looking through the list of electrolytic and paper caps and there are a few that I can't seem to find anywhere online or in my catalog, what else can I use in place of the Dual 15-15 mfd 450/150 volt caps? The closest I've found so far is a single 16UF @ 475 VOLT or dual 16/16 µF @ 450 VDC on antique supply. Just want to make sure I'm replacing these with the right stuff..

Anthony
KB3RJH

[W3NP]

Just a small update and a question...

Well, got the new power cord installed on the VII last night so that should be good to go, not putting the other end on till I get the caps replaced. Was looking through the list of electrolytic and paper caps and there are a few that I can't seem to find anywhere online or in my catalog, what else can I use in place of the Dual 15-15 mfd 450/150 volt caps? The closest I've found so far is a single 16UF @ 475 VOLT or dual 16/16 µF @ 450 VDC on antique supply. Just want to make sure I'm replacing these with the right stuff..

Anthony
KB3RJH

The values are not real critical and the older caps had a huge tolerance range. The closest current standard size would be 20 or 22 uf and either of these these would be fine, and 30 or 40 uf wouldn't hurt. You could save some money and use 250 or 350 volt units for the old 150's. I usually go with somewhat larger capacity values when recapping.  I would just use single units, as special dual caps are usually much more expensive.

[w4bfs]

power supply questions seem to be the most frequent .... maybe its because its the common point of the system ... are you staying stock, especially with regard to using vacuum tube rectifiers? ... this question is pivotal because it will drive how the rest of the power supply is done ... if this were my first restoration, I would stay with stock until everything is working or failures are identified ... power supply filter cap values can vary considerably (+ 100%, - 20%) without consequence because the stock caps generally had that tolerance .... modern caps tend to hold a tighter tolerance, especially when operating at less than rated working voltage .... I would use an Illinois 22 uFd 500V for the 15 uFd (and have in my VII's ) and they work fine ... keep asking questions and research old threads ... 73 ...John

[KB3RJH]

Excellent! I was hoping the tolerances were high so I could sub other (affordable) replacements in there. The dollar signs and the XYL shaking her finger at me were already popping up in my head...

I plan on keeping it stock until I get it up and running. Run it through it's course for a while to give me some time to get used to it and then possibly give it an upgrade with the few mods I've found for better audio and whatnot... Just gotta get to the running stage first... 

I know I'm going to have to modify the 160 in/out pot a bit, it's got some deep grooves in the shaft and the knob won't hold on anymore. Going to try to put a bit of a flat spot in it so the screw holds better (ahh the Dremel tool!). At least that's how I've seen a lot of modern pots designed to keep the knob from coming loose. Any other suggestions would help..

[W3NP]

I know I'm going to have to modify the 160 in/out pot a bit, it's got some deep grooves in the shaft and the knob won't hold on anymore. Going to try to put a bit of a flat spot in it so the screw holds better (ahh the Dremel tool!). At least that's how I've seen a lot of modern pots designed to keep the knob from coming loose. Any other suggestions would help..

The 160 in/out "pot" is actually a wafer switch driven by a pulley/dial cord affair. You probably need to clean out and lubricate all of the bushings where the shafts pass through and the switch bushing itself to get rid of the excess friction or drag. The knob is no doubt slipping because too much drag is present. My VII "160 in/out" knobs turn fairly easily. It is a good idea to clean all rotating shafts of old hardened grease when doing up an old piece of gear.

Yes, as I mentioned in a previous post - you are doing the right thing by getting it up and running in a near stock fashion before beginning the mod process.

73, Dave

[WA1GFZ]

VII works well with covers removed and sitting on its side. Many have spent years in that position....just be careful. You can do 1 change at a time and test the results.