Johnson Viking I checkout.... help!

[KX5JT]

Okay, so this is my first "project" with tube equipment.   I had basic tube theory in tech school 24 years ago but never used it in the real world.  I just don't want to spin my wheels when I can draw upon the vast expertise of the members of this forum.

History:  Bought a Johnson Viking I in unknown working condition 2 years ago from eBay.  It is in fantastic cosmetic shape, all the tubes and components seemed intact.   Carefully removed the tubes and wrapped them in paper towels and boxed then shelved all of it for future checkout when I have the time/space to get into AM.

Recent history:  Getting into AM.  Put the Johnson Viking on the bench over the X-mas holidays.  Wired a lightbulb (150 watt incadescent bulb) fixture to a small length of rg-8x and a pl-239 for a dummy load.  As I was putting the tubes back into their sockets I cracked the 6AL5.  Call out to the local AMers with the ricebox yeilded a new 6AL5 in my mailbox sent by a kind soul (Thanks Jack, AD5VO). 

Tonight:  Put the 6AL5 into it's socket, installed 3 crystals (3880, 3885 and 3890), plugged in the power cord.  Read the tune up procedure in the manual and followed the procedure for 80 meter tune-up.... Got the Buffer and the Grids looking good as expected in the manual.  Turned the drive down to 0-- turned the meter to plate current, flipped on the plate voltage.... headed to full scale and the plate on the 4D32 getting quite cherry red!  This with no key attached and drive still at 0.   That's not supposed to happen!  WHOOPS!... turned it all off and checked the troubleshooting guide...

Closest thing in troubleshooting section is "High 4D32 plt current with Key up: a.) A fixed bias failure is indicated.  Check 6AL5 tube. 
**** It's new, but who knows, besides this is before keying up!****

What would you experienced AMers do here?  Could it be I need to replace all the paper caps?  Hey, I see caps in there that don't look like anything we used in 1985 to present... not sure what the paper caps look like!  I know there are mica and electrolytic caps in this thing! (or Condensors as the manual calls them). 

As I have no real-world local Elmer, I am just looking for some friendly guidance, thanks!

KX5JT

[WQ9E]

Start by replacing the bias filter caps (C12 and C13), these little electrolytic caps are almost certainly bad.  The originals are two capacitor sections in one case but you can replace them with two discrete caps.  While you are in there I would also replace the B+ filter caps (C10 and C11).  These were all originally 16uf caps but the current standard value of 22uf will work fine.  The bias caps must be rated for at least 150 volts (you can safely go higher and there is plenty of room) and the B+ caps are rated for 450 volts.  Be careful and observe polarity when installing the new caps; for the bias caps positive goes to ground while for the B+ caps negative goes to ground.  Reverse the polarity and the 4'th of July comes early.

You might also want to replace the 10 uf cathode bypass cap on V1 as it has probably lost capacity by now.  Use a 50 volt rated unit and negative goes to ground for this one.

Once you do all of this check the bias voltage with a meter before turning on the HV to avoid hurting the 4D32.

Most of these vintage transmitters use a shorting jack for the CW key so if there isn't a plug in the jack it is just like having a key plugged in and closed.

Also take a good look at the 5R4 sockets and the bottoms of the 5R4's while you are in there, they are prone to developing carbon tracks from dust.  If you find them before they get bad you can easily clean them.

Make sure you have the proper sized fuse so it will protect your transformers from some failures.

Finally, enjoy the Viking 1.  It is a rugged transmitter and has a really cool looking case.  I bought one several years ago to pair with my SX-28A and recently another one adopted me.

Rodger WQ9E

[WA1GFZ]

never turn your Drive to zero. It is not like a SS rig. You need Grid current to bias the final into class c.

[KX5JT]

never turn your Drive to zero. It is not like a SS rig. You need Grid current to bias the final into class c.

The tune up procedure says

r. ........ After the buffer has been properly adjusted, turn "driver" to it's 0 position.

s. Turn meter to "plt" postion and "plate" on.  Turn "drive" clockwise until  plate   current rises to 150 ma.

This is where the problem is.  During "s." when I switch "plate" on, the plate current starts immediately rising to full scale without applying drive yet... and the plate becomes cherry red.


As a side note, my "filament" lamp is not lighting although the filaments are lighting... any idea where to get a replacement front panel filament lamp? 

KX5JT

[WA1GFZ]

yup bias problem. I still would not key up without any grid current.
Like doing hole shots at every light.

[Pete, WA2CWA]

never turn your Drive to zero. It is not like a SS rig. You need Grid current to bias the final into class c.

The tune up procedure says

r. ........ After the buffer has been properly adjusted, turn "driver" to it's 0 position.

s. Turn meter to "plt" postion and "plate" on.  Turn "drive" clockwise until  plate   current rises to 150 ma.

This is where the problem is.  During "s." when I switch "plate" on, the plate current starts immediately rising to full scale without applying drive yet... and the plate becomes cherry red.


As a side note, my "filament" lamp is not lighting although the filaments are lighting... any idea where to get a replacement front panel filament lamp? 

KX5JT

This tune up procedure for this area is the same for the Viking I and Viking II as per their manuals.

Before screwing around changing capacitors, etc. check the bias supply. You don't need to flip the HV (plate) switch on. The bias supply operates off the low voltage transformer. See if you're getting the 3 negative voltages as described in the schematic. For the final tube, the -75 volt output is the important one. According to the Parts List, the filament lamp is listed as L2 (#40 miniature screw bulb).

[KB2WIG]

FWIW, ya can pop in diode(s) to replace the 6AL5


klc

[KX5JT]

Okay the underside of this transmitter tells a story.  It's going to need some TLC.  There are still paper caps (okay so those are obvious, paper electrolytics right?) in the audio section.  The audio driver transformer has some leads that have even broke off due to age. 



http://i271.photobucket.com/albums/jj131/kx5jt/Viking%20I/VikingI001.jpg

[W1AEX]

Your Viking One chassis looks pretty nice. Much cleaner than mine was when I first opened it up. After you identify and resolve the issue with the bias, I would suggest the shotgun approach. Replace all those ancient carbon resistors and any electrolytics or paper rolled caps you see. I remember when I first poked around inside mine that when I went to bend a resistor out of the way, it just broke in half and crumbled. When you get done you'll have a great transmitter that will run trouble-free for a long-long time.

The driver transformer with the crumbling leads could be an issue. As I recall, when mine failed many years ago, I pulled something out of an old Fender amp that worked fine. I'll bet the Hammond Company might have something that would work.

http://www.hammondmfg.com/claspg.htm

Good luck!

Rob W1AEX

[Ed/KB1HYS]

Point of Procedure.  I can't see in the photo, but make sure that there is a 3-wire plug in there and you've got a ground (safety not rf) attached.  With the red wirenuts it is sure someone replaced the cord. make sure your safe before you start probing voltages.  make sure the replacement cord hasn't somehow bypassed the fuse holders either (if one was installed).

[Opcom]

The picture reminds me. That big blue resistor there by the PA is known to go bad. If someone did add a grounding plug, good. It is a pain in the butt as I recall. There still may be a capacitor from each side of the AC line to GND there. Sometimes those short and cause the chassis to get hot. Under no-signal conditions the 4D32 is supposed to be completely cut off by the -75V bias. If it is not, check the screen voltage, it might be high.