Viking II High Voltage problem

[WV9R]

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. 

[WV9R]

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

[ka3zlr]

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.........

[WQ9E]

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

[ka3zlr]

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....

[WA1GFZ]

6AL5 was the bias rectifier in my V2.

[WV9R]

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  . 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....

[WV9R]

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

[WQ9E]

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

[WV9R]

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

[WQ9E]

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

[WV9R]

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

[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

[WQ9E]

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

[WV9R]

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

[WA1GFZ]

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

[WQ9E]

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

[ka3zlr]

Well done Roger..

[KM1H]

P.S. Whenever you use a big bypass cap at the base of the plate choke to gnd its better to use a .001uF (1000pf) and not a .01uF for an HF xmtr. It actually works best if you use two separate 500pf caps, one on the topside of the chassis and one on the bottom side underneath.

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

[W7SOE]

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

[KM1H]

 

A total of 1000pF (1000uuF) is usually the correct value to bypass the RF at the base of the plate choke on an HF transmitter.

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

[N3DRB The Derb]

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.

[KM1H]

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

[W1EUJ]

Fight! Fight! Fight!

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

[W4RFM]

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