Help Viking 2 problems

[N8OKR]

Hi all my Viking 2 tunes up per manual no problem 100 watts carrier. but when I try to modulate carrier power goes down with modulation. The mod current seems to be in order but the plate current drops about 20ma. with audio peaks. Ive changed the modulators, and the 5r4's. The carrier is also folding back on the scope and no foward power on a peak reading meter. The rig does not blow fuses so not shure of it is the mod iron or not?
Thanks De N8OKR Terry

[KA3ZLR]

Hi,

I will take a Gamble here and offer you might have it tuned to tight a 100 watt's is fine BUT BUT
dropping your power down a little like tuning over Peak for a drop in power might yield you a Forward signal. try Dropping the drive back a little it's called Head Room..leave space for the swing.

Providing all is well in board ..


73
Jack
KA3ZLR

[N8OKR]

KA3ZLR, Thanks for the advice but lowering the drive for head room produces the same results just at a lower carrier level.

[KA3ZLR]

O.K. Try readjusting the output controls move them around while it's keyed till you
find the sweet spot an whistle watch your meter for a swing it's in there you just
have to find it. right around 90 watts is what you want..

Also watch your coupling yuo may have to much or to little depending on the load your
putting signal into.

[WQ9E]

I would leave the drive at the rated level but tune up for about 80 watts or so out (slightly less loading) and see how it does.  Drop the mic gain as necessary to avoid over-modulation at this reduced power level.

If you haven't done so already, make sure the 5R4 sockets and tube bases are clean to avoid carbon tracking, arcing, and transformer loss.

[KA2DZT]

May be a power supply problem.  Try loading it a little less.  HV may be dropping too much on mod peaks.  May even be bad filter caps.  If you can, measure the HV with a digital VM.  Then switch the meter to AC and read the amount of AC on the DC.

Make sure you have enough drive.  Check the drive current with modulation, shouldn't move around much.

Let us know what you see.

Fred

[N8OKR]

I will check the voltages and see what i find. I dont think its a tuning problem as ive tuned it this way for over a year.. I have a little more info I should have put on the original post. The kids got in the shack and turned on the plate and fil. switch with no antenna connected. When I found it the fuse was blowen and one of the 5r4's had a blowen filament. I change the 5r4's and this is the result..
N8OKR

[KA3ZLR]

Oh Boy That we didn't know Gud Luck O.M.

73
Jack
KA3ZLR

[KA2DZT]

With the AC unplugged,  check the resistance of the HV transformer secondary.  You may have an open half winding.  HV power supply may be running at half wave instead of full wave.  That would give you poor regulation and possibly cause the problem you have with the power dropping on mod peaks.

Fred

[KA3ZLR]

WOW,.. as well check all wiring one by one for any signs of Melting...check the antenna wire

your gona have to go through that thing piece by piece how long would you say this was on..?


73
Jack
KA3ZLR

[N8OKR]

I dont know how long the rig was on like that could have been days. I guess it depends on how long it took to blow the fuse. BTW the fuse was the correct amperage. Ive checked every thing visually and nothing looks melted or burned. Ive even isolated the mod iron from ground thinking that the windings might have been arcing to ground but no dice..
DE N8OKR Terry

[KA3ZLR]

Welp, if all the Iron checks out all Toobies are up to snuff...There are no issues of any bad Voltage
readings anywhere That big Resistor underneath  not cracked or anything Bias is Holding up...?

All it leaves is Caps. in my estimation...Caps or a Bad connection somewhere but I'm not there can ya get a pic up on here..?


WOW...


73
Jack
KA3ZLR

[KA2DZT]

Terry,

Check the power supply especially since you had a blown fuse and a blown filament in one 5r4.  Check the HV xfmr to see if both halves of the HV winding are still good.  Hopefully, if the rig was in transmit with no antenna, the finals are still OK.

It's unlikely you have a short because you've had the rig back up and running.  Your problem with downward modulation is likely a power supply problem.

Fred

[W7POW]

Time to have the kids go out and pick a nice switch.

[KA2DZT]

If the power supply checks out OK,  I would take a look at the loading caps.  A xmtr running with no antenna would have put higher than normal voltages on the output circuit,  this may have damaged something there.

Fred

[steve_qix]

Hi all my Viking 2 tunes up per manual no problem 100 watts carrier. but when I try to modulate carrier power goes down with modulation. The mod current seems to be in order but the plate current drops about 20ma. with audio peaks. Ive changed the modulators, and the 5r4's. The carrier is also folding back on the scope and no foward power on a peak reading meter. The rig does not blow fuses so not shure of it is the mod iron or not?
Thanks De N8OKR Terry

Ok, one question: Do you get any modulation at all on the carrier as indicated by an oscilloscope or other credible monitor?  If NO, it sounds as if you have a short across or in the modulation transformer, primary or secondary.  Could be a bad transformer, or IF there is a capacitor across one of the transformer windings , you have a shorted capacitor.

The fact that you're getting 100 watts of carrier [I'm assuming you're reading output], and I am assuming the plate current is more or less normal, that your power supply is supplying the requisite voltage and the problem is in the modulator itself.

Any shorts to ground would result in the transmitter being non-operational.  Bad loading caps, et al would preclude a good carrier output.

All indications are a mod transformer problem, or shorted cap across the transformer.  Could also be bad wiring (a short across the transformer), a short across a terminal strip, a bad CW/AM switch (or the switch in the CW position  ).  A VERY outside thought would be driver problem, where the driver transformer somehow failed, and both tubes are being driven in the same phase - as I said, a very outside chance, but it would give EXACTLY the same symptoms as a shorted mod transformer.

Hope this helps!

Regards,

Steve

[KA2DZT]

Tnx Steve,  I'm running out of ideas.

I think he said he was getting modulation, but his plate current was dropping about 20ma on mod peaks.  This drop is what he said was the problem.  So, I was thinking the HV PS is not up to 100%.  Also, he claims he had a blown fuse and blown filament in one of the 5r4's.  I'm thinking something went south in the PS.

I'm assuming he didn't have any audio input when his kids turn the rig on with no antenna, therefore there would not have been any audio on the mod iron secondary.

OTOH, maybe his kids were screaming into the mike hoping for a reply.

Until we here what, if anything, he may have figured out, I'm not sure what could be the problem.

Fred

[KM1H]

If youre lucky its just that the audio section paper caps and associated electrolytics finally gave up...or did you change those earlier and didnt mention it?

The driver transformer is more likely to go than the mod iron, its way undersized to start with.

Id also check the bias and the 807 screen voltages.

Carl

[Knightt150]

Sounds like the HV power supply is not up to power, If you have not changed the electrolytics in the HV supply for a long time or just had the radio setting around for some time, change the HV caps.

John W9BFO

[WD8BIL]

Solid state the HV rectifiers and add some more capacitance to the HV supply. Both the modulator and final run off the same supply and mod current will suck down the voltage on the final.

You can lessen this buy tuning up with a tone (1kc is good) and watching for best peak on a scope.

[KA3ZLR]

It was stated it was left on for awhile till the fuse blew that could have been quit some time
coulda been a fire...good thing it let go.

I would Replace all the condensers in the power supply and associated circuits for obvious reasons.


73
Jack
KA3ZLR

[steve_qix]

The thing is, we don't actually know if there is any modulation.... The only information we were given about this is that the carrier level decreases with modulation, the peak reading meter does not increase, and there is a reference to "folding back", the meaning of which I do not fully understand 

We're dying out here - we need more info

Or, you could put it in your car and drive up here to Massachusetts, where we'll fix the problem, and when you leave the Viking will sound like a broadcast station    (yes, it will still be a tube rig!)

Regards,

Steve

[N8OKR]

Hi all problem solved it was a shorted cap across the modulation transformer.Thanks for all the help
DE N8OKR

[steve_qix]

Hi all problem solved it was a shorted cap across the modulation transformer.Thanks for all the help
DE N8OKR

That's great!  All symptoms pointed to a short across or in the mod transformer.  Glad it was just a cap and not the transformer itself   

[K5UJ]

Hi Terry I heard you on 3885 this evening with the V2 and it sounded real good. I think you showed up right after I called it quits but still had the rx on.

73

Rob