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Viking II dumpster find




 
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Author Topic: Viking II dumpster find  (Read 4392 times)
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k7mdo
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« on: April 07, 2016, 06:30:18 PM »

I have been for quite some time trying to assemble "one" Viking II from a pair found in a dumpster. 

Finally got power to one today after going through the obvious problems, only to find a "BIG" problem I fear. 

When the power is applied I hear a "cooking" sound inside the low voltage transformer (T2).....  sounds like someone is frying eggs in there.  I quickly pulled the 5V4 and every thing settled down... all filaments lit, no more transformer hissing.....

I had measured the resistance of the LV windings and none were open but it appears that that isn't the whole story...

Maybe there is some good news as I have the LV transformer out of the other Viking II found in the dumpster along with this one....

However, it looks like a bear to change... any thoughts? 

It isn't a "hurry up" project and I don't need it as I have a third Viking II CD that I revived a couple of years ago and it functions just fine.

73, Tom

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wb3eii
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« Reply #1 on: April 07, 2016, 06:40:45 PM »

no help from me here, i just want to know where you go dumpster diving. 73
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KO6YB
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« Reply #2 on: April 07, 2016, 08:03:37 PM »

Strange that pulling the rectifier stopped the frying. Could it be a very shorted  5V4 or the filter capacitor after the 5V4 is very bad (shorted out). If there was a short in the transformer winding, it would have continued to fry after removing the 5V4.

Stan
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w4bfs
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« Reply #3 on: April 07, 2016, 08:10:48 PM »

it is possible that even though stressed that lv xfmr may still be ok ... remove all loads from it by unplugging rectifiers and other tubes .... even remove pilot lamps ... once you are satisfied that it is unloaded then ballast it with a series connected 60 to 100 Watt incadescent lamp with clip leads ... when lv powered the lamp should only glow dimly ....this is good .... let it run several hours this way and carefully note the case temp .... it should only get slightly warm .... see if you can measure output voltages, carefully also noting the hv xfmr may exceed 900V to ground .... definate electrocution hazard ...be very careful
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Patrick J. / KD5OEI
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« Reply #4 on: April 07, 2016, 08:24:58 PM »

sometimes a light or odd  or malfunctioning load will make a current that causes the transformer to make noise. Possible things to try:

1.) check the filter choke to make sure it is good. If it is internally shorted of turns the current spikes on filter charging can make noise.

2.) power the set with an external and metered B supply and see if the set works. Then you can see if there is a noisy fault that is causing the transformer to repeat the noise.
For this I use two regulated tube supplies in series, but any decent plate transformer, rectifier, and cap bank can be whipped up and controlled with a variac for this test.

3.) check the DC voltage and DC current on the rectifier output. Then remove the rectifier and use a power resistor across the total secondary to load and draw the same current and see if the noise is still there.

4. )When this noise is being made, is the center tap of the transformer ungrounded such as by a standby switch or relay? Sometimes a small amount of leakage or corona or the like can make a small but noisy current that is amplified by the transformer. The defect could be anywhere, inside the iron, across the switch, etc.. dirt and humidity.

5.) Instead of swapping the transformers, hook up a bunch of clip leads dangerously to substitute the transformer winding of the other set, and see if that transformer is made to sizzle. This is after you have eliminated any potential shorts.

These tests may help find out why or where the noise is being made.
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steve_qix
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« Reply #5 on: April 07, 2016, 09:07:07 PM »

Like many have already said - if the transformer stops frying when you pull out the tube, it's probably good!  The CT of the transformer is grounded, so any transformer short would continue with the frying.

Sounds like a short after, or in the rectifier.  Probably a shorted filter cap, filter choke or some other component in the L.V. system.

Good dumpster diving job for sure!
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k7mdo
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« Reply #6 on: April 07, 2016, 09:51:27 PM »

alright, this all makes a lot of sense....  I have not checked the filter choke to round, but did replace all fo the filter caps with new....  but further checking is warranted....  I did see the oscillator current rise for a second or two before the first "snap" somewhere put a cork in that.... the sizzling sounds lie it is in the transformer as I explained but .....

I did check the 5V4 and it showed OK.... but you never know, I will check the new filter caps and the LV filter choke....  so I am not as worried as I was... might try the light bulb trick tonight if I can get the gumption...  I have a lot of hours into the thing to just "re-dumpster" it... 

I was actually pretty excited to see the other filaments all light up as this transformer is the filament supply as well....

No end of fun.

I won't re-dumpster it! Too many great parts for my CDC that I use a lot.

On a brighter note, I got a Hallicrafters HT-37 at the last hamfair a couple of months ago... looked like it had sat for a long time but it actually cleaned up nice and is being very well received by its audio on 75 meter DSB phone...  pretty tickled with that anyway.

Thanks for the thoughts, 73, Tom
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KB2WIG
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« Reply #7 on: April 07, 2016, 10:07:18 PM »

Sockets! Sockets he bleated!!!!!
Check for cruztys around the rect socketz

KLC

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N9axl
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« Reply #8 on: April 07, 2016, 11:07:13 PM »

I would agree it is some low voltage component. That you hear the noise in the transformer can be deceiving since there are bunch of components in there. I would start with l1 and l2 and go from there. 

I've been working on a Viking 2 CDC for months and months - with a lot of help - and it still hasn't fired up completely. But these things are really built like tanks.  Is it possible you have a bypass cap that is shorting to ground?  That kind of short can sound like a sizzle. I've been advised previously to get a good magnifying glass and examine everything carefully. You may see carbon tracks or component cracks you are missing.
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k7mdo
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« Reply #9 on: April 08, 2016, 12:21:36 AM »

Well, this evenings inspection revealed open circuit on the audio driver transformer... primary side.  Got a spare but it makes worry what else I missed in checking wiring....

The tube sockets are clean... the chokes test fine and a quick voltage check downstream revealed about 300 vdc before I got scared of noise...

Got tired so moved away for the evening... Will remove and replace the little audio interstage tomorrow as the spare tests patent on both sides.

Sweating the modulation transformer but finding no opens or shorts yet.

Tom
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M1ECY
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« Reply #10 on: April 08, 2016, 03:22:26 AM »

Measure the voltage coming off of the transformer each side of the CT, with the rectifier removed - the voltage either side of the CT should be virtually identical.

If there is any more than a volt or two mismatch you most likely have a shorted turn in the transformer (an all to common problem on older transformers)

This will give all of the symptoms that you describe so far.

Cheers
Sean
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WZ1M
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« Reply #11 on: April 08, 2016, 04:50:41 AM »

Lets not forget, that transformer was not built for 120/122 vac. Plate voltage runs high, filament voltage runs high.
Regards,
Gary
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k7mdo
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« Reply #12 on: April 08, 2016, 06:50:14 AM »

My line voltage is reduced to 110. VAC .

I have avoided the high side at the tube socket as I will need to break out the Heathkit VTVM as it reads up to 1500 whereas the Fluke won't go over 750 without repair.... I did notice a resistive difference either side of CT but thought that made sense depending on how the transformer was wound.

All chokes test fine.

Unfortunately the 5V4 tube socket is underneath the RF coil and bypass mess surrounding the incoming line voltage....  maybe should have removed that stuff as RFI is the least of worries. If it is the transformer then that stuff will have to go to get at the wiring.

We'll see.

Tom
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DMOD
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« Reply #13 on: April 08, 2016, 12:07:13 PM »

And while you are checking things don't forget the fuse. I have found quite a few "over" fused.

You know the old saying, "If an 5 Amp is good enough then a 15 Amp MDL oughtta be better."  Wink

I use a  3-5 Amp fast blow when first bringing any Viking II series up on a varactor. Fuses are cheap, transformers are not.

Phil - AC0OB
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kg7bz
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« Reply #14 on: April 08, 2016, 01:23:30 PM »

Hearing "frying" from inside the low voltage transformer that goes away when the 5V4 is pulled, could indicate leakage (arcing) to the core from the 5V filament winding for the 5V4. Pulling the rectifier removes the 300V DC from that winding.
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k7mdo
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« Reply #15 on: April 08, 2016, 02:56:15 PM »

OK, measured HV at the sockets for both the LV and HV transformers... they seem correct in that I have 250 VAC both sides of CT on the LV and 775 VAC both sides of CT on the HV transformer...  I find no leaks that I can measure from filament to HV windings but... that is not for sure....  I find no "shorts" to ground in the LV circuits though there is some problem around the audio section that I have yet to deal with as the little interstage primary is "open" but I thought I would leave that alone until I can get reliable LV in the circuits...

On looking at the LV transformer I at first thought it would be a real bear to change out but after more concentrated observation, I see I can do it, especially if I sacrifice the AC line filters to get them out of the way.... I am not ready to give up on the old transformer completely but plan to fire up the "spare" one out of the other dumpster set to be sure it is "live".... 

Hard to imagine the abuse there two sets must have gone through to end up in the trash when they were essentially complete. 

Worse than any of this is that the wife has me headed off for two weeks swimming with the fish (?) in the Amazon River, then Machu Pichu where propagation might be OK but ham radio will have to take a back seat.  So it will be unlikely for me to work on the Viking for a little while but I will get right on it when I return.

Thanks for the ideas so far, 73, Tom
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KA2DZT
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« Reply #16 on: April 08, 2016, 10:17:00 PM »

I think the dumpster Viking II might be the least of your problems.  I'd be a little more concerned about your wife's idea about your swimming in the Amazon River.  Is this something she wants you to do or is she going to be swimming with you??  I would suggest that she go first.  If she fairs out OK, then maybe you can take a dip.

Fred
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KX5JT
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« Reply #17 on: April 08, 2016, 10:26:55 PM »

*huh?*
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AMI#1684
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« Reply #18 on: April 08, 2016, 10:51:26 PM »



There is quite the difference between "swimming with the fishes" and "sleeping with the fishes".


klc
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w1vtp
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« Reply #19 on: April 09, 2016, 07:03:20 PM »

Enjoy the swim  Grin    Grin


* piranha-copia.jpg (64.73 KB, 429x287 - viewed 125 times.)
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WD4DMZ
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« Reply #20 on: April 12, 2016, 10:46:32 AM »

Hello Tom. I recently acquired a Viking 2 and you might be able to help me. It is up and running well but it had a bug that destroyed the L21 rf choke at the base of the large L7 choke that leads to the 6146s. I fortunately had one so am back on the air.

There are actually 5 of them in the radio. In addition to L21 are L14, 16, 19 and 20. The others are under the chassis and can be seen around the octal power output socket. They look like large, brown resistors and mine have a wide yellow and purple band on one end.

My request... since you are working with 2 Vikings to make 1 could I purchase one or two of the chokes from you? The one on the coil is hard to access unless you remove it but the ones under the chassis are easy to access. You would probably want to keep a few spares yourself in the event you fry one.

Also, might you have any xtals for the AM windows you might want to part with?

Regards, Rich
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k7mdo
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« Reply #21 on: April 12, 2016, 06:51:51 PM »

Yes, I know the choke, it was. also burned out in mine.   The one I am rebuilding...  I am in Peru right now but when I return I will email to make contact to get a spare to you.  Tom
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WD4DMZ
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« Reply #22 on: April 12, 2016, 07:12:25 PM »

Thanks for the reply Tom. Drop me a note when you return.

Regards, Rich
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DMOD
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« Reply #23 on: April 12, 2016, 07:17:38 PM »

Hello Tom. I recently acquired a Viking 2 and you might be able to help me. It is up and running well but it had a bug that destroyed the L21 rf choke at the base of the large L7 choke that leads to the 6146s. I fortunately had one so am back on the air.


Regards, Rich

Since you will most likely be replacing C32 and C46, also located at the bottom of L7, go ahead and replace L21. One can tell of an impending failure of L21 by the black band in the middle.

Do NOT use a choke with a higher current rating because this choke also acts a “last chance” protection fuse for L7.  I used the Murata 11R472C 4.7 uH RF choke available from Mouser as Mouser part number 580-11R472C. I replaced the two caps with 0.047 uF at 2kV for better high frequency response.

You have to cut the HV wire to the bottom of the choke from the wiring side in order to remove the choke.

I set up a new connection point just above the 6146's with a 2-lug terminal strip and new wire to the choke since the old wire's insulation gets very brittle.

Phil - AC0OB
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« Reply #24 on: April 13, 2016, 12:26:13 AM »

That is the info I was looking for.

Thanks, Rich
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