My Viking II is on the air again but I have some questions.

[KX5JT]

Hey everyone, so I went nearly a year thinking I had a shorted out LV transformer when smoke came out of the area where it sits last winter.   With the help and advice of a few hams (thanks Don, K4KYV, Clark KE7TRP and Brandon K5IIA).....I started going through it and found the 5V4G rectifier was bad.  It had a short from one of the plates to cathode, the top inside envelope had some carbon black and the glass envelope was not sealed very well... allowing the smoke out.

Well I found a broken solder joint on the buffer tuning cap, so I took care of that.  I also had some issues plugging my dowkey into the back so I traced it to terminal strip and simply used to heavy wires and soldered some break out wires for it, bypassing that old connector on the back panel.

So it's up and making RF on the air and with the Valiant mod xfrmer and audio mods, getting great audio reports.  I do notice just sitting idle the LV transformer gets pretty warm.  Is this normal?  I can touch it for a while but if I press really hard on it I could probably only keep my finger on for maybe a minute before it's just too hot for me.   It could be normal since the LV powers all the filaments and other things even while idling.  Just want some verification on this.

Here's the remaining big issue.  I'm working around it by just turning off plate switch and manual moving the fine coupling cap because the cord that operates it from the knob on the front has come loose.  It looks like in order to REALLY get that cord back on it's wheels, I'll need to remove the front panel.  Anyone have experience with this?  I think I'll need to soak the set screws with some penetrating oil... man, I don't want to strip them or crack knobs but they are TIGHT.  Looks like meter escutcheon and main loading escutcheon have to come off....... there is nothing in the manual about how to actually do this.  I want to get it done but I'm wary of proceeding!!

Anyway, I able to work around them but the cover has to remain off, so any hints, guidance or advice will be welcome!

John

[N8ETQ]

  Hey John,


The Johnson Viking 2 Manual dated July 1953
pg. 21 lists Normal voltage at various points
in the rig.

US AC line Voltage around that time was 110/220.
For an interesting read about US AC line voltage
over the years please see this:

http://www.w8ji.com/power_line_voltage.htm

Your LV Xfmr is burning up. They will run pretty
warm but..  You will NEED to take steps to reduce
your AC input back down to 115 VAC. The drive control
is the weak link in the LV supply and was barely
sufficient for the job back in the day, but at
least they were new. Now all that stuff is 60 years
old!

Below I list some voltages that, from a simple
mathmatical viewpoint demonstrate how high
AC line voltage is burning up your rig. I also
added the dissapation of R25 in the LV supply.



Filament Ckt.


115 / 6.3 = 18.25 : 1 turns ratio.

6.57 @ 120

6.68 @ 122

6.79 @ 124


Low Voltage  310VDC Nominal @ 115VAC input.

R25 the "Drive Control" is the bleeder for this.
25K WW pot usually rated at 4 W.

310 @ 115   3.85W

323 @ 120   4.17W

328 @ 122   4.3 W

334 @ 124   4.46W


Plate supply 660VDC @ 115VAC

690 @ 120

700 @ 122

711 @ 124


If your rig has been Re-capped with modern electolytics
you can expect these voltages to be even higher.

As far as the front panel is concerned, it's not that big
of a deal. These were kit's designed for simple assembly.
The knobs can be an issue however and I suggest you go
and buy a new screwdriver. Worn out tools can really
wear out and damage small set screws. With a properly
sized and sharp tool you can usually get those screws to
crack loose.

GL and 73

/Dan

[WD5JKO]

Dan,

   You make a compelling case towards controlling the incoming line voltage. I wonder how you feel about using the HV Rectifier filament winding (5V 4A load) to buck the incoming AC voltage down by 5 vac? This also gets the HV off those windings. Of course then the HV (and perhaps the LV) would have SS rectifiers. If the LV gets SS, an additional R-C might be needed to reduce the LV B+ back to ~ +310v.


Jon,

   I heard you and Brandon on last night. Brandon with his SDR "Apache", and you on the V2 sounded great. I tried to break in twice, but you guys were quick with the switch. Later I worked Ralph KD6OS (Porum Ok.), and Steve WA1QIX (Mass.) on 3878. I had to drop 7 Khz since you and Brandon were strong enough (er...wide yet clean!) to make 3880 "too close" to you guys at 3885.

Jim
Wd5JKO

[N8ETQ]

  Hey Jim,

      Oh Yeah, Besides bucking the input down you are
also removing a couple Amps of load off the LV Xfmr.
That combination will certainly help.

      Not sure it would be enough though, the two
components that are most likely to fail are the
transformer and drive pot, both are pretty hard
to come by. I was fortunate to come across a GRC
AC Line Voltage Regulator last fall but prior
to that bucked my ac line with a 12.6 xfmr that
brought my test bench  down to about 112 VAc.
Switching to SS Rectifiers will also raise the
voltages a bit.

http://amfone.net/Amforum/index.php?topic=40930.msg298433#msg298433

     My antique test equipment likes it very much.

      A MOSFET can replace the drive pot but
a better solution may be to regulate the LV with
a MOSFET.  I'm using a circuit from WA3DSP article
on the Ranger. Works great.

http://www.crompton.com/hamradio/JohnsonRanger/RangerModsSchematic1_2-5-2013.pdf

     Full article:

http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html


     For equipment I like to leave ON, I try to get the
Fil voltage just under 6.3 .  I was lucky to find a
replacement PA tube for my HP 608-D which failed due
to open fil.  Would hate to have to open my URM-25's
to change out those as well.

Thanks and 73

/Dan

[KX5JT]

Hey thanks for the responses!!  I knew I could count on this board!  

Dan, I am running my Viking II on one of those new red Chinese Variacs.  It's a wonderful little device and for the money brand new I think it's pretty neat.  I tested the with my VOM and the meter on it as well as the dial pointer do seem to be well calibrated.  I'm running at 115 volts AC.  Maybe I should drop it down to 110?  It only gets that hot after sitting on for a few hours and being used intermittently.   I'm do see the original oil filled capacitor is in the circuit.   It is running the original original tube rectifiers, the 5v4g for the LV (Just changed out after the old one shorted) and some vintage 5R4's for the HV.  The oil filled capacitor (c9) is still in place and with the choke input HV supply.  

Okay I'll try to dial down to 110V input for it and see how she works.   I suppose I need a long and small screwdriver for those set screws and some penetrating oil.   I'll look for one at the Harbor Freight soon.

Jim, sorry we need to drag our feet a bit more and allow some other stations in.   The problem I have on 75 meter AM at night on the weekends is the groups just get too darn large.  Brandon (bless his heart, I know he's going to read this) loves the Old Buzzard Transmission thing.   Myself I like a medium, you know a few minutes, 5 seems to be the most I enjoy gabbing during one round, but some guys like to go for a while, maybe even passed their 10 minute without ID'ing mark.   But that's fine because the stations that do that are usually easy listening and easy copy and I certainly enjoy that.

Well I'm up and at them here in the early afternoon today for the 7.160 group.  I'm not usually awake at this time but what the heck I got to bed a bit early so I hope maybe I can catch a few of the "locals" on 40 AM this afternoon.

John

[WD8BIL]

Just in case. Elliott Electronics has 25K 5W WW pots for $12. I have one in my Viking 1 and it works great.

http://www.elliottelectronicsupply.com/5-watt-wire-wound-potentiometer.html

[DMOD]

If you don't mind adding two, 6-lug terminal strips, here are some Viking II mods I use on my Viking II's in order to reduce ripple on the DC and to stabilize voltages.

Phil - AC0OB


Update: Added Modulator

[KX5JT]

Ah  yes very good information!!! The Viking II is doing very well at the moment.  I may consider the mods at a future time.   My main focus is getting that front panel off now where I don't crack the knobs or strip the set screws.  I noticed one or two of the set screws are Bristol types, the rest are regular flat head screws.  I have a Bristol wrench set on the way and I'm using some penetrating oil.  Dial cords that come loose SUCK.