Viking II R13 / R30 Questions

[WA1LBK]

I'm in the early stages of restoring a Johnson Viking II I acquired at NEAR-fest a couple of weeks ago; the obvious problem was a missing (& very deteriorated anyway!) AC line cord.  After installing a 3-wire AC cord, with some crystals that were already in it, I was delighted to see over 100 Watts of RF out on 80 & 40 M.    Planning to run it on 75 M. AM, I found I had no modulator current; a quick check showed R13 open, which I guess is a common problem with these.  Finding a replacement R13 isn't an issue; Galco Electronics has a replacement listed for $13.63.     My question is on my rig, R13 has not one but TWO adjustable taps, & R30 appears to be non-existent (as an it appears to have never been installed).
I just located R30 on the schematic, at least (PDF I found online).  Any one have an idea if this was a production change in the Viking II?  What is the second tap for on R13?  Any help would be appreciated.      Thanks!  Tom, WA1LBK

[DMOD]

It sounds to me like it got hamboned, as I have never seen a double tap on R13.

BTW, going up to 25k or 30k on R13 and increasing all the filter caps to 47 uf gives improved hum reduction, assuming you are using the tube rectifiers.

I would also recommend checking ALL the circuitry closely and according to the schematic as there may be more than just this "visible" mod.

The tap was primarily for setting the screen voltage on the 807's to about 285 volts, as I recall. Setting this voltage also affects the voltage at the R30 6AQ5 clipper so these items are interactive.

Phil - AC0OB

[WQ9E]

R-30 is the adjustable pot (mounted on the chassis top) for the clamp circuit. Is the 6AQ5 clamp tube present?  That circuit was part of the changes from the Viking 1 and should be part of all Viking 2 production. 

Where does the second tap on R-30 lead?

I would convert it back to the stock clamp circuit.

[KB2WIG]

The VK2 that I had, had the "double tap"...  Watt it was, was an attempt to bridge over a spot where the  wire wound round the ceramic body had been broken. The two taps together taped off the appropriate voltage.


klc

[WA1LBK]

WOW! Thanks for all the quick responses, guys!  (Just joined AMfone, this is my first post here!  ).  But the mystery deepens... not only does R30 appear to be absent, but the socket for the 6AQ5 clamper tube (which should be socket X28, according to page 41 of the PDF manual I downloaded) is not there either! Again, its not a case of the socket being removed; the hole where socket X28 should be (between the socket for one of the 807 modulators X3 and the loading capacitor switch SW6) is non-existent.    The remainder of the tube layout agrees with the PDF manual. 

I haven't yet traced out where the second tap on R13 goes to...been getting over a cold  which hit me the night before NEAR-fest (felt lousy enough that I thought I  might not have been able to make it up there; fortunately did, as I not only acquired the Viking, but also did very well selling that weekend as well.    I'm on the mend but kind of alternating between days when I feed decent, then last night had a 1/2 hour coughing fit which left me dragging most of today  , so I'm hitting the sack early.   I'm too tired tonight to do it, but I may actually take a couple of photos of the chassis & post here them as well.  Thanks again for the help!    Tom WA1LBK   

[KA2DZT]

Tom,

Welcome to the AM Forum.  When it comes to working on old boat anchor rigs, the folks on here should have the answers to most any problem.

Get well, and we'll wait for your next question.

Being that you're new to the forum, I'm not 100% sure, but I think there is a limit of three smiley faces you can use in any one post .

Fred

[WQ9E]

Tom,

The Viking 1 did not have a clamp tube but I remember seeing an introductory article about the Viking 2 which showed that the change from a 4D32 final and the addition of a clamper circuit were the primary changes made to create the Viking 2. Either your unit is some sort of design prototype or perhaps a Frankenstein created by a ham using V1 and V2 parts.

What does the final compartment area look like in terms of tubes/sockets?  Any chance you have a Viking 1 chassis with a Viking 2 panel?

[WA1LBK]

OK, feeling a bit better tonight.  Here's a few photos:

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=794

The front panel logo does say "Viking II"

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=795

Front panel overall view.  The crank knob for the roller inductor was missing; for the time being at least, I substituted a knurled knob.  All other knobs are original.

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=796

R13, showing the two taps.  Resistance measurements (with a Fluke 77 DVM) show it completely open.

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=798

The 807 modulator tubes looking from the rear of the chassis.  Note no 6AQ5 socket X28 or R30!

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=797

Under-chassis view of the 807 sockets; again, no R30 or 6AQ5 socket!

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=799

Top view of the finals.  They are 6146's.

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=800

Overall view of the RF area, including crystal sockets.

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=800

Rear view of the cabinet; although the front panel isn't too bad, cabinet rear & left side paint is a mess!  I plan to repaint the cabinet after I finish the electrical restoration.
The new 3-wire AC line cord is visible.

http://amfone.net/Amforum/index.php?action-gallery;sa=view;id=800

Left side of cabinet.

That should give you guys a decent idea of what I'm dealing with.    Tom WA1LBK

PS - Having a bit of trouble trying to embed the photos, the "Photo" button didn't appear to work.  Just look in the gallery under my call to view the images!

[KA2DZT]

Tom,

What happen, only three smiley faces.  Was just kidding about the limit-of-three rule.  Feel free to use as many as needed.

Wish I could help a little with the Viking II.  I never owned one, so not able to help.

Fred

PS Tried but was unable to locate any pictures of the rig. 

[Pete, WA2CWA]

PS Tried but was unable to locate any pictures of the rig. 

Do it this way:
http://amfone.net/Amforum/index.php?action=gallery;su=user;cat=106;u=50628

[K9PNP]

Tom,

The Viking 1 did not have a clamp tube but I remember seeing an introductory article about the Viking 2 which showed that the change from a 4D32 final and the addition of a clamper circuit were the primary changes made to create the Viking 2. Either your unit is some sort of design prototype or perhaps a Frankenstein created by a ham using V1 and V2 parts.

What does the final compartment area look like in terms of tubes/sockets?  Any chance you have a Viking 1 chassis with a Viking 2 panel?

IIRC you are correct about the V1 to V2 changes.  It appears to be a V2 chassis minus the clamp tube.  Even the 'obsolete' schematic for the V2 shows it and the 6146's.  If this is a converted V1, whomever did it was really good at metal working since the oblong hole for the 6146's looks like original as from the factory.  I also have never seen a double variable-tapped R13.  I will continue to look around for data, but as of now I am officially stumped.

[WQ9E]

Mitch,

I am sure prototypes existed and you may own one.  It will be interesting to see where the second resistor tap leads.

In my first V1 there was a neatly installed clamp tube so the original owner felt the need for one.  But these transmitters do have significant standing bias on the final and should withstand a brief loss of drive if the owner is paying attention.  If I had a Viking 2 without the clamp circuit if the chassis was in clean/original condition I would leave it as is.

[KA2DZT]

I think if you look close at the resistor, the second tap on the resistor is jumped the other tap.  Probably jumping across an open spot.  Adding a second tap clamp is not uncommon on WW resistors.

Fred

[K9PNP]

Rodger - I was referring to LBK's V2, not mine.  Mine is mostly stock.  Sorry if I mislead anyone.

[ka4koe]

"When it comes to working on old boat anchor rigs, the folks on here should have the answers to most any problem."

...except how to extricate oneself quickly from a transmitter's innards when the XYL comes a callin'......."Honey, are you up there???...."

[WA1LBK]

OK, haven't had much time the past several days to chase things further until tonight, decided to take a few power-off resistance measurements to try to get some idea how this unit differs from the PDF schematic I've got.   For starters, the two taps on R13 are not tied together.  From what I've read so far, I gather the purpose of the "clamper" 6AQ5 V28 is a screen voltage regulator for the 6146's (someone correct me if my assumption is wrong  ).  Since I've got RF output, I'm also guessing I'm getting screen voltage to the 6146's (it's been quite a few years since I've done much vacuum-tube troubleshooting  ; have to remember this is very different from the low-voltage SMT stuff I deal with at work so trying to be particularly careful poking around for voltage measurements so I don't become like the "Hare Krishna's" & "receive enlightenment!!   At this point, trying to track down where the 6146 screens are being supplied from since V28 is non-existent on this unit; there is a relatively large 4.7 ohm carbon resistor directly off the 6146 grids, then a bypass cap to ground on the far end of the resistor, also a black wire which runs off into the wiring harness.  Next step is to chase down the other end of that wire, but running out of time for tonight  , & doubt I'll have a chance to get back into it until Wednesday evening at least.  "Stay tuned" for further developments...    Tom WA1LBK

[WQ9E]

Trace where the leads from the resistor taps go, I am sure one goes to the 6146 screens through an additional dropping resistor (if any of the clamp circuit was ever present) and the other may feed the modulator screens but tracing is the only way to be sure.

The 6AQ5 clamp tube is designed to protect the final if excitation is lost. When there is excitation additional final grid bias is developed and a sample of this is fed through a balance/adjust potentiometer to the 6AQ5 control grid cutting off the 6AQ5 tube.  If excitation and bias is lost then the 6AQ5 will draw heavy plate current and it is fed from the screen side of the screen dropping resistor so it drops or "clamps" the screen voltage to a very low level  protecting the final from damage.

[WA1LBK]

OK, finally had a chance to do a little circuit tracing tonight, particularly in regards to the two taps on R13.  BOTH taps go the CW / PHONE mode switch on the front panel.   It appears that the mode switch selects which tap is used on R13; there is also a sizable wire-wound resistor (measured it at 20K, looks to be @ 10W. judging by the size) mounted to the second wafer of the mode switch, which gets switched in series with the second R13 tap when the switch is in the CW mode. (I took a photo of this area of the chassis & will post in my folder shortly).  I'm not particularly concerned  with operating this rig on CW  (I'll use my modern rig, an ICOM IC-756, if I want to run CW  ), so I can probably just leave the second tap disconnected when I install the replacement for the open R13.  Just tried ohming out where the screens of the 807 modulators are fed from - they're connected to the #1 (higher voltage) tap on R13 when the mode switch is in the "PHONE" position.  Since I know R13 is open, this is presumably why I don't have any modulator cathode current or modulation - hopefully, replacing R13 should get this thing up & running on AM.  I'm also going to take Phil's earlier suggestion about increasing R13 to 25K & going to 47 ufd. caps to minimize hum as well.  I'm going to try to see if I can get the parts ordered this weekend.    Tom WA1LBK     

[WQ9E]

Tom,

I wouldn't completely ignore making the rig operational on CW.  Generally tune up is done in CW and it is also useful for testing/diagnosing transmitter issues.

[WA1LBK]

Ordered the replacement for R13 (took Phil's suggestion & went with a 25K wirewound over the original 20K) earlier this week, UPS tracking indicates I should have it delivered by Friday.  (If they do manage that, should have time to install it this weekend).  If I can salvage the 2nd tap clamp from the original R13, I'll try to keep it original which should hopefully restore CW capability as well.    May also change out some of the electrolytics, & the 100 ohm resistors in series with the 807 modulator grids (one measured at 150 ohms  , so it'd probably be wise to change them both out).  If those part replacements get it restored operationally on both AM & CW, my next step is going to be removing the cabinet for wirebrushing, sanding, & a spray-can repaint.  There's also an obvious mod with some shielded cables brought out the back of the cabinet & terminating in a round military-style plug; looks like the original owner may have been tapping B+ & filament voltages to run an external VFO.  Not crazy about B+ being brought outside the cabinet  , so planning to disconnect that.  Was planning to order "rocks" for 3875 & 3885 KHz. once I'm sure it's runnning OK, but am going to consider coming up with a solid-state VFO of some sort; may start a separate thread looking for recommendations on one.    Tom WA1LBK

[WA2ROC]

The Viking II already has low voltage and filament voltage available at the octal plug.  That's where my 122 VFO plugs into.

If the shielded wires have true HV (750V or so) I'd get rid of them ASAP since there's no practical way to use the HV outside of the case. 

There's a switched 110 VAC plug on the back that can operate a 110 V relay for antenna changeover and receiver muting but it uses a socket that will fit a crystal holder or maybe a set of tip jacks.  Not one the crystals used in the VII (FT-243 if I remember) but one of those crystals with smaller and closer spaced pins.  Find one that fits, strip out the crystal part and wire up a 2 conductor wire for the antenna relay.

[K9PNP]

The 110 VAC socket on  the rear panel takes an HC-6/U crystal style plug.  I made my own out of a bad crystal.

[Pete, WA2CWA]

Antenna relay wire with connector: http://k9sth.com/uploads/Johnson_Reproduction_Parts_1.pdf

[WA1LBK]

Got the new R13 (25K, 50W) installed tonight.  Fired it up & I now have have modulator current.   - Initially 80 ma., powered it down & made sure the HV was discharged, & re-adjusted the R13 tap until I got to 60 ma.  For the time being, left the 2nd R13 tap disconnected.  The new R13 has only a single tap clamp; thought I might be able to recycle a tap clamp from the old R13, but the newer one is physically smaller than the original, so unless I modify that clamp can't connect that additional tap.  Tried both hooking up a mic & using my iPhone as an audio generator  (Yes, "There's an App for that!"  ), still NO modulation at this point.    Tried swapping out the two 6AU6's with some NOS ones I had; no change (& swapping out the second one - V2 - was far tougher than replacing R13! - That damn tube did NOT want to come out of the socket!) - & trying to get my big arthritic hands in there didn't help!  (Finally managed to improvise a tube puller with a piece of rubber & large long-nose pliers!).  Still no audio at this point but calling it quits for tonight, got to hit the sack.  Next step will be voltage & component checks in the audio stages.    Tom WA1LBK

[KA2DZT]

Try to see what the second tap is supplying voltage to.  It may be voltage going to the audio chain and may be why you have no modulation.  I have rubber tube pullers.  They come in handy when you need one.

Wondering if that second tap is a stock connection or a mod someone added?

Fred