The AM Forum

I recently purchased  a clean Viking II, upon getting it home and trying to tune it up the plate current was around 400ma no matter what was done. The HV rectifiers were replaced with solid state units and the LV rectifier has a 5R4GYB tube in place of the 5V4G. ???  We tested and found no bias voltage to the tubes. That was traced back to a bad solder joint and was repaired. Before repairing the bias problem I followed the procedure to adjust the clamp tube. While checking the modulation current the fuse blew. Now everytime I flip the switch to bring in the HV the fuse blows right away. Has anyone else here had a similar problem or can steer me in the right direction of where to start looking? Thanks in advance for your help. 

Yep, the fuse still goes instantly with the 6146's and the 807's removed. I'm concerned that it is the Modulation Transformer. Anyone have any idea where I can find a replacement if it comes down to it?   Thanks

We replaced the rectifiers with solid state replacements then went onto adjusting the clamp circuit....after a poor solder joint condition was discovered..on an unkown xmitter claimed to be in good working condition......pulled tubes and still a problem.....lift one leg off the mod tranny out of circuit make sure yer power supply is proofed first.. then start jumping around...that tranny in mine has taken a beaten at times...when i ran it...boy i hope that isn't yer problem OM...but there are plenty of them around for parts on epay...

Hey if'n ya need one let me know...i'll yank one out of one of mine ...what kinda traden material ya got...

 Oh one more thing I leaned the hard way....when solid stating things....it's good to have a "VariYak" around.........

Were enough rectifiers in series used for the solid state HV rectifier replacements?  Pull your SS replacement rectifiers to make sure that one or both has not shorted.  With power plug pulled short the HV to ground to discharge the oil filter cap and then measure the resistance to ground to see if it is correct.  If not isolate the fault to which component is causing leakage to ground.

Make sure your problem isn't a short to ground at the connector for the T/R relay since it is only energized when the plate switch is on.  Finally, try pulling the 6AQ5 clamp tube (with the finals still out of course) since the clamp circuit is also activated through the HV supply.

Rodger WQ9E

When Discharging HV LV supplies...CHASSIS OF PIECE TO BE GROUND CONNECTED TO OUTSIDE GROUND PRIOR.."ONE HAND IN POCKET".... HIGHLY INSULATED SOLES ON SHOES...I do Not use broom handles wood retains moisture... Use a piece of highly insulating factor tubing and the device that does the shorting to be of substantial material to handle the current attached to the end heavy rubber glove is also a Big benefit...

Make yer connection from a safe distance...That Condenser carries enough current to Kill...

If we're going to discuss discharging things with the membership Safety is a Priority....

6AL5 was the bias rectifier in my V2.

Thanks for all the suggestions.  I'm on my way back down now into the depths of the basement shack to dig deeper. I understand about discharging the caps, I'm a high voltage electrician by trade, worked on a 1500 volt DC 4500 amp catenary system here in Chicago. We used large caps mounted outside on the steel support structures ..I had enough seniority that I was always able to have someone else do that job  ;D . I then went into the safety department at th same railroad and I am now the Manager of Safety for the other commutter railroad here in Chicago. So you dont have to tell me twice to be safe ..well that was work ..this is my chosen hobby ..I do it for relaxtion..yea thats it ..I had a very relaxing day yesterday.... ::)

Well it's early and I dont type ..or sometimes spell too good ..sorry forthe typos and spelling in the previous post .  :-[

Also add check for carbon tracks on the 5R4 sockets to your list of things to check, I had that issue with my first Viking 1. 

Rodger WQ9E

Hi all,  Well here's the update. I took the both of the primary sides of the modulation transformer off. Put in a new fuse and it held.  I reinstalled the 6146's and it held. I reinstalled the 807's and it held. I took readings on the mod transformer and all seems good. So I sat back and scratched my head, while doing so I looked at the connections for the mod transformer once more, the purple wire comes from R13, connects to the strip with the mod transformer by it self. The other primary side has 2 white wires with a green trace on them that were connected together where it connected to the mod trans., so I hooked those 2 back together, without hooking up the mod trans., and fired it up. Bam blew the fuse, so I unhooked then and traced the wires out. One goes to the CW/PHONE switch, checked it for a ground, it was good. The other white/green trace goes up to the HV choke behind the finals. I checked it for ground and it shows 8 ohms to ground. This wire hooks at the bottom of the HV choke, there are also 2 caps there going to ground. I disconnected the top of the choke from the doorknob cap on the tank circuit and also the leads going to the top of the finals. Still shows 8 ohms to ground. I reattached the mod transformer, without the 1 white/green wire and fired it up and the fuse holds. The only thing that makes any sense to me, thats not saying much at the moment,  is that one or both of the caps at the bottom of the HV choke have gone bad?  Make any sense to anyone else ..any suggestions on what I'm not seeing...oh and by the way ..the HV is 842 volts.  I think I need to get those solid state rectifiers out of there ..agree ..disagree ??  I'm going to go and hit my head against the wall, I mean enjoy this hobby for a bit.  Thanks again guys I really appreciate all of this   Ray

Ray,

It sounds like you have found your problem, a shorted bypass cap.  Going from the mode switch towards the final you should have a .01 bypass to ground then L21 which is a little VHF RF choke then another .01 bypass to ground at the bottom of L7 which is the RF choke in the HV feed to the final.  Disconnect both of the .01 bypass caps and see which one is shorted, I would replace both of them at this point with 1500 volt or higher rated caps.

Your HV is a bit high but of course that is the unloaded value and it will drop under load.  You could either add some series resistance or go back to the 5R4 tubes.  Since 5R4's are readily available I would go with the tubes.  In either case you will need to check and probably re-set the tap on R-13.  Be careful as the wire on R-13 is quite fragile.

Rodger WQ9E

Hi Rodger,  Yep you are exactly correct.  It was the bypass cap on the vhf choke. But as you suggested I'm going to replace both as well as go back to the tubes. Any suggestions on a better replacement? Again all of the help I've received here is greatly appreciated. After I have the Viking II up and running hopefully I'll get the chance to catch up with everyone on the air, well almost everyone.   Just to fore warn you guys though, the next project is the Thunderbolt amp....Thanks Ill keep everyone updated on the progress when the parts arrive. But Rodger if you have any suggestions on replacements or values please let me know .. Thanks
                         Ray WV9R

Hi all,  Been looking at Antique Electronic Supply and they dont list the 5v4g low voltage rectifier, is there a replacement that everyone is using ? Havent had a lot of luck finding anything. Thanks
                                   Ray WV9R

Ray,

I order most passive components from Mouser (www.mouser.com)  They are a very large supply house with no minimum order and fast shipping.  They have a number of suitable capacitors, one style that I use is the Xicon brand ceramic disc.  The part# is 14-202P9-103K-RC for a .01 @ 2000 volt cap for $1.51 each.  Radio Daze (www.radiodaze.com) lists the 5V4G for $15.00 and the 5V4GA for $10.50.  However, you could just keep your solid state replacement and add a series resistor to account for the typical voltage drop in the tube.  The voltage drop across the 5V4 in the Viking is not that high so a 180 ohm 15 watt resistor from Mouser (280-CR15-180-RC ) for 63 cents added in series between the cathode lead from the 5V4 socket and the input to the filter (the junction of C11 and L2) should put your low B+ back where it belongs.

Rodger WQ9E

Hi Rodger,  Thanks for the reply, I've bought from both Moused and Radio Daze before. The solid state rectifiers in my Viking are the HV side and someone used the HV tube in the LV side.  Thats why I'm looking for a 5v4g.   I fgured that I'd put that back in the LV side and put the proper ones in the HV side too .   Thanks Ray WV9R

at 100% positive peak you will be at 1500 volts. I used .001uf 3 KV caps.
They had been replaced before.

A couple of comments:

Higher working voltages never hurt but the Xicon caps I recommended to Dave are specified to survive  2.5 times the rated working voltage of 2,000 volts and are designed to pass a 1,000 hour life test at 2X working voltage so they should have no problems living in the Viking 2 where the original caps are 1500 volt units.

A comment about the "filter", L-21 (a 4.7 micro-henry choke) and its associated .01 bypass cap were added as part of the TVI reduction strategy applied by Johnson (these do not appear in the Viking 1 but were added to some Viking 1's as part of the "TVI kit" released by Johnson).  If you don't have neighbors without cable (or who listen to weak FM broadcast stations) then you could remove these two parts but they really do no harm.  L-21 impacts only VHF frequencies (just use one of the many online calculators to examine the reactance of a 4.7 micro-henry choke at lower frequencies if you want to check the purpose of it).  However under no circumstances do you want to remove the other .01 capacitor because it is the RF bypass for the primary RF choke L7.  Because of the high distributed capacitance across the windings of L7 it is fairly ineffective as a choke at VHF so L21 was designed to help prevent a raid by the "Tennessee Valley Indians".

Rodger WQ9E

Well done Roger.. :)

That works to dump any VHF that works its way around the choke but does nothing for lower HF/MF that gets thru via strays. I use a .01 2kV and a .001/3kV in my Viking 1. Went thru the complete TX with a Measurements 59 sniffing for bad stuff and found plenty that required caps and ferrites.

I had a Viking 1 with the factory kit in the late 50's and it still caused some TVI even with a LPF (discounting the TV 21 mc IF's) . This one doesnt bother anything on any band.

Carl
KM1H

Ray,
I wish I saw your post earlier, I had the same bad caps on my JVII. I am glad you found your problem.

73
Rich
W7SOE

 
I really dont understand your statement since the Viking II schematic shows a .01 uF bypass for L-7. IMO L-21 should have a .001uF bypass added.

Your quote cant be used as a blanket statement. In the Vikings the XL of the choke probably follows the old 10X rule but doesnt guarantee that some HF RF will be getting into the PS, shielding or not. The .01 uF as shown is simply good engineering.

The Johnson built 6146 sockets are designed to be submounted, it has nothing to do with TVI. If they were dropped 1" or so on standoffs it would be to shield the grid leads from the tank circuit and eliminate the need for neutralization. This was often done with 807's or 1625's as practiced in the ARC-5's.

In modern RF amps the plate choke XL is often in the 3-5X ratio of the RL of the tube(s) and is actually calculated (by the better designers) to be part of the output network. Dual chokes are sometimes employed in either switched or series configurations. In those cases a .001 uF is completely inadequate for much of anything below about 20 or 40M. Several amps (Dentron and the other bottom feeders past and present) try and get away with a .001 uF but 80/160M efficiency suffers and adding a .01 uF brings the power up to what it should be. At QRO a HV .01uF is not cheap at retail but 6 and 10kV ones sometimes show up in surplus.

Carl
KM1H

dont forget that the Viking 1 had a bug in the driver circuit that caused a HUGE spur centered on the frequency for TV video channel 6 - they had both a factory copper screen mesh tvi kit and another factory kit to install in the driver stage to quash the channel 6 bug, both eliminated in the V2.

Have it your way Brian and Im not a damn dude either. I didnt say that the sockets were mounted in the II for neutralization BUT they have been utilized that way in several other 2E26, 6146, and sweep tube rigs.

Yes, Ive been familiar with the Viking I bugs and fixes since the late 50's. With this one I have the benefit of HP gear to check the audio and RF spectrum as well as distortion. There is no need to monkey around with sloppy basement engineering to get top performance.

Carl
KM1H

Fight! Fight! Fight!

KM1H, W5HRO, school parking lot, 3 o'clock.

Hey Ray,
If you need a rectifier tube, I have several pulls, and I will send you one freebie.  Just let me know.
Bob

longest post wins!!!!!!!!!

PHD - Piled High and Deep.

Ok is the Posturing over... LOL...;D

Did he get the transmitter fixed..? that's all i wana know...I got an extra Mod tranny if he needs it....Junxton Junk... ;D

up here in 1 land it is "piled higher and deeper"

Well, of course it would be, in 1 one-land.

But up here its frozen solid until the spring thaw. Down below it keeps getting deeper and riper.

Carl

Hi all, wow lots going on here ..well I replaced the caps and I am waiting on a rectifier tube..once I get a tube I will check the clamp tube adjustment and see what happens ..hopefully I dont let any smoke out. I'll keep everyone updated as I go ..and if you see a mushroom cloud in the direction of Chicago...hopefully it wasnt me.  hih

Ray,

When you get it going let us hear it on the Midwest Classic Radio Net which meets on Saturdays at 7:30 A.M. local on 3885.  Unless your tube is coming overnight I guess we won't hear it tomorrow morning  :)

Enjoy the snow tonight and please keep it upstate!

Rodger WQ9E

Hi Rodger, Nope no tube yet...I'll try to keep the snow up this way, but dont want you to get sleet or freezing rain ..my son is on his way back to school down there by you. I'll let you guys know when the tube arrives and I will get on the net ..Thanks Ray

Hi Ray,

We got the freezing rain but not enough to cause any problem except for the roads.  I am a prof at Illinois State and classes start Monday for us.  Looking forward to hearing your Viking 2.

Rodger WQ9E

Hi Rodger,
       Thats where my son is going, in his 2nd year, he's not sure what he wants to do yet, but I'm not suprised.  I told him he should check and see if there is a radio club on campus. Well hope the weathers better for you than us all week .  Ray

Ray,

Have him look me up sometime.  If we cannot draft him into the College of Business I will be happy to put him in touch with someone in the proper college.

Rodger WQ9E

Hi All,  Well I was able to borrow a 5v4g tube and got the Viking II fired back up ..it tunes nicely with all of the currents as per the manual, except one, I have no modulator cathode current, the manual says, in the clamper tube adjustment, that it should be set to between 60ma and 80ma, I have none, notta, zip....down in this section all of the resistors and caps have been changed. Not sure if a mod has been done or not. I did notice though that R10 and R11 are 200 ohm, not 100 as the print shows. I'm going to download the mods , I think there were 2 of them , and see what I can figure out , if anything hihi...does anyone know what voltages I should be looking for on the pins of the 807's, I know I'm being a pain in the ass asking all of these questions, but this is really my first endeavor into this type of transmitter. Any help as, always would be greatly appreciated.  Thanks Ray

Ray,

Typically I would suspect a problem with the tap setting on R-13 which sets the screen voltage for the 807 modulator tubes, you should typically have around 250-270 volts appearing on the screen grids.  The fixed bias should be around -37 volts on the modulator control grids, and the plate voltage should be around 620-640 with the final loaded to rated input.

While you are checking this I would suggest doing so with the modulator tubes removed from the transmitter since you don't need them in place and you don't want to damage them.  I would suggest first measuring the control grid bias at the tube sockets (you don't need the plate/HV switch on for this and make sure it is within +/- 15% of -37 volts).  If this is good, then you need to measure the other tube potentials.  Since HV is present at so many places on top of the chassis in the Viking 2 I strongly suggest you connect your meter with all power off and then power up to make your measurement and remove power before removing your meter leads.  I would not bet my life on the bleeder resistor so after powering off and before connecting any leads wait a minute or so and then short the plate supply to ground.  Then set up and  measure the screen voltage and if it is very low then you need to find out why, whether it is simply a need to reset the tap on R-13 or if there is another issue.  If the screen is good, measure the HV at the plate caps again exercising extreme caution.

The value of R10 and R11 will have no significant impact on the resting current of the modulators.

Rodger WQ9E

As a update:  Both of the audio mods that I found required changing the tubes out. Both of the tubes that I have a 6au6a's, so if a mod was done the tubes were not changed, does anyone know of a mod that left the tubes the same? Thanks Ray

Thanks Rodger,  I also noticed it appears that someone removed the resistors in the leads going to the caps of the 807's, or was this a resistance type of wire?  Thanks Ray

The mods by Thomas Bonomo, K6AD, in ER mag a fews years ago, used the original audio tubes, with a phase inverter tube added as part of stage 2 mod. The ER issues are 110, 111, and 112. I am planning these changes for my Viking II when basic repairs are complete. (time? what free time!?)
Norm K7NCR

Hi Rodger,  Looks like I have some other issues, On the leads going to the caps of the 807's I have 740 volts, I dont see any screen voltage, and I see two negative voltages, one in the 72 volt range and one in the 55 volt range. On the yellow and green lines of T3, I'm reading -72 volts and past R10 and R11, on one I'm reading -55 and on the other it's still -72...think I need to shut down for the night and regroup..I also measured voltage on the tap of R13 and got a negative reading there too ...I keep telling myself this is my hobby ..I enjoy this ... ;D

Hi Ray,

Part of the fun of the hobby is the feeling of accomplishment after you "slay the dragon" that is harassing you  :)

Based upon what you have found, first a couple of questions and then some suggestions:

1.  Are the bias capacitors new and near the correct value (not over 22uf for the input capacitor C13)?
2.  Are you still using a 6AL5 for the bias rectifier or has it been replaced with SS diodes?

I am assuming that the answers to 1 and 2 are yes.  If so, check the values of resistors R15, R16, and R17.  These provide the bleeder and voltage taps for the bias circuit and it sounds like 1 or more have drifted high in value since the center tap on T-3 is being fed with too high of a voltage.

Are you making the measurements past R-10 and R-11 with the 807 tubes in or out of socket?  There should not be any significant current flow through the control grid lines on these two tubes so if the tubes are in you have a tube problem and if not there almost has to be an issue with the socket, even if one of the two resistors went way up in value you should not be measuring much voltage drop since the only current flow should be through your meter.  I am assuming you are using a fairly modern meter with at least a 20,000 ohm per volt sensitivity and more likely a 10 megaohm input from a DMM.

The abnormally high HV reading combined with a negative reading on the tap indicates that R-13 is probably open (or disconnected for some reason).  Remove power from the transmitter and short the HV to ground, then remove the short and measure resistance to ground.  If it is over 20K ohms (and it is likely well over this) then your bleeder resistor R-13 is open or disconnected.

Rodger WQ9E

Hi ..R17 is not droppingthe bias voltage at all.  I clipped on side and temped in a 4.7k, all I have and the bias dropped to about -30 volts. I'll have to check R13, but it's off to work in the snow now ..hopefully the roads are not too bad, I drive to Michigan City Indiana, right in the famed "snow belt", it can be bright and sunny here, but there it could be a blizzard if the lake effect snow machine turns on. I'll post more tonight.  Thanks

Heres todays update:  I replaced R17 which is suppose to be a 2700 ohm resistor, well mine tested at 110 ohms, so changed it and now I have -41 volts of bias at the 807's so thats all good. I checked around and found a cold solder joint on the 6aq5 and after cleaning and resoldering  I have 202 volts getting to the tube.  The tap on R13 still shows a negative voltage. I tested R13 and it was at 19,600 ohms.I still have no mod current or from what I can see screen voltage at the 807's. I'm seeing this schematic in my sleep ...something is not calling my name, and I hope it doesnt reach out and slap me either hihi...any suggestions would be greatly appreciated...it coming along one small step at a time.  Thanks Ray

Hi ..I've got a question...on the HY plate switch there are 4 wires, at least on mine. 1 is white with orange/blue trace 1 is white with silver/red trace 1 is black and 1 is orange, now where the orange wire is there was another wire that has been cut, can anyone tell me what it was and where it should be going? I cant fined the other end anywhere ..Thanks Ray

Ray,

Since you have high voltage but you have negative voltage on the R13 tap, either the tap is not making contact with the resistive wire on R13 (is it loose) or R13 is not connected to the high voltage.  So check and make sure that one end of R13 is connected to the HV bus, the other end is held slightly above ground by the metering shunt sh1.  The top end of R13 should have the full high voltage on it and the tap is set to provide the screen voltage to the 807 modulator tubes; it should be a few hundred volts positive with respect to ground and not negative. 

One side of SW-2 applies power to the plate transformer, the other side is used to ground the cathode of the oscillator tube V6 so that it is operational when the plate switch is on, it is also connected to the accessory plug on the back to provide a switched ground for the external VFO to activate it for transmission.

Your modulator screen voltage should measure high if the 807s are removed since there is no current through the screen dropping resistor..
Light load the high voltage will be high. Mine runs 760 with solid state rectifiers. Check the resistance of the big slider resistor. Many times someone set it too tight and broke the fine resistance wire. A negative voltage could mean it is open at the tap. be very careful if the resistor is open because that is also the HV bleeder and it will hold a charge for a while after you unplug the rig.

I want to thank everyone, espically Rodger for all of the help I received. I cleaned R13 a bit and cleaned the contact on the band and now I have mod current. :D I adjusted it as it says to in the manual in the procedure for adjusting the clamper tube. I'll finish the adjustment tomorrow and see what I end up with ..if it all looks good I'll put the rest of the case back on and see if I can get it on the air...if it all works out good it will be on the the Thunderbolt to see what condition it's in ..I havent even plugged it in yet ...one project at a time... ;D  I'll post tomorrow ...hopefully with good news!

Ray, 

Congratulations on getting it going and you are welcome.

I have heavier vintage gear but the Thunderbolt is the most awkward to move about and work on because you cannot remove the heavy plate transformer without also unsoldering a number of wires.  Be very careful with it given its high voltage and be sure and have it unplugged and the HV grounded while working on it.

Lubricate the fans in it, they probably were not properly lubed in years and are getting old and need all of the help they can get.  I had one of the same type fans that went up in a smelly cloud of smoke in my Desk KW a few months ago.  I added inrush current limiters (available from Mouser or Digikey) to reduce the turn on stress on the transformer.  Mine is used with a Johnson Pacemaker and an RME-6900 receiver; it makes a nice vintage SSB station and works OK on AM.  I don't know if you are planning to drive yours with the Viking 2 but if you use it on AM you will need to swamp the output of the Viking 2 and you are generating a lot of heat for about 6 db gain of RF so I don't really think that is a good application for the T-Bolt, on CW it is worthwhile since you can run the T-Bolt in Class C and get around 700 watts out.  The T-Bolt is well suited for a low power SSB rig like a Central Electronics 10 or 20 series that also runs AM or it would work well with a Drake 4 line or similar controlled carrier AM transmitter.

Rodger WQ9E