Johnson Viking II Ham transmitter Modulation problem arching high voltage shorting quick fix

Recent project brought to D-Lab from a fellow in Detroit. Transmitter has developed a high voltage fault. Could be a shorted modulation transformer, hopefully not. Replacement parts for these vintage transmitters are becoming sparse. I expected the worse, turned out to be a minor repair. The EF Johnson Viking II is the 57 Chevy of transmitters. Very nice robust design. They will out live us. Just require a little TLC now & then.

[bobblum]

Thanks, Terry. Those solid state rectifier replacements are a good example of "equivalent replacement parts" not being the same as originals. I've seen ECG replacement transistors that cross-referenced but had more gain than the originals, causing self oscillations. It's best to use as close to original and avoid needing to modify the circuit.

[edwardhannigan]

Top work as usual Terry...Great fix, and information..Mic is clear also..Keep them coming..Ed..U.K..😀

[f.k.burnham]

I have seen postings of many case histories of numerous failures of the modulation transformers. Quite possibly it was caused by the use of SS HV rect.

[NebukedNezzer]

I use 5r4 rectifiers is all my vintage transmitters. good tip and good video. I like the lapel mike fine.

[VintageElectronicsGeek]

Terry - Just an FYI, the correct pronunciation for "RODE" is "ROAD" ~Jack, VEG

[kenhancock]

FIRST THX terry hope your having a great day!!! your videos with uncle doug and brad the guitarlogist is helping me get through a tough time.

[umajunkcollector]

I like the camera mic too, two cents for my comment.

[davidstinson]

Thank you for this, Terry. I love my sturdy Viking II.
The Viking II is "Steak and Eggs" vs. the DX-100 "Vegan Soy Burger."
Don't like the Heath DX-100 and I won't work on them anymore.
Everything in it is run right up to "the hairy edge."
There's just no excuse for running 1625s at 800+ Volts.
The terminal strips and wire are the cheapest they could
find and are always 5 seconds from arcing-over.
The VFO can't be still and there ain't much you can
do to correct it, because the root of the problem
is cheap mechanical materials with no thermal properties.
The transformers are weak milk-toast, just dying
to roll-over on you. There must be a zillion
smoked-up DX-100s sitting in garage corners,
waiting for the grand kids to send them to scrap.
Give that DX-100 to your local Chicken Bander.
Get yourself a Johnson Viking II and be happy.
You can fix it with a pocket knife and a forked stick.
TNX OM ES 73 DE Dave AB5S

[coltronex]

The microphone you are using sounds like its lacking high frequencies, does not sound crisp, just an observation Terry

[hitechredneck]

Nice repair, Terry...quick question - did you end up replacing those cracked VFO resistors?

[zulumax]

Nothing quite like the smell of burning Bakelite, only to be topped by a smoking selenium rectifier.

[kerryg]

I've been watching your videos a long time now and I never thought there was anything wrong with your audio before. Still sounds good but to me not worth the hassle of the wires hanging around.

[kevincleary]

The Lab has good hearing for being outdoors (5:49).

[mackfisher]

Success good show Terry
Saw your lab, in the background you need to consult with him more often, there is nothing like a wise old dog to add to the team.

[LarryDeSilva]

Replacing the 5R4's with semiconductors was a bad move on his part. You are right he is indeed lucky that he didn't smoke the transformer. I have a DX100 that some guy modified as well it also had 5R4's but he had messed it up so bad I put it back to original and it works fine now.

[melvinreaser]

Thanks, Terry you are definitely the Mann I did find another transformer & I will definitely buy it anyways perhaps the whole transmitter I'll give you call soon

[submarineradioman]

Interesting Terry! My DX-100 blows a fuse when I throw the plate switch. Haven’t found the problem yet. Maybe (hopefully) a similar problem. Tnx de Howie WA3MCK

[rciancia]

Terry, that mic sounds much better !!! If the option exists, I would decrease the bass a little or increase the treble. You gotta love the old carbon trails.... Nice job as usual Terry. Loving the new audio setup Dlab V2. :)