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Viking Valiant 811As for modulator




 
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Author Topic: Viking Valiant 811As for modulator  (Read 637 times)
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KD6VXI
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« on: September 08, 2018, 07:13:15 AM »

Have a Valiant on the bench.  Highly modified, to say the least.

Power xformer has been replaced with a Kenyon T-668.  1KV and 750V AC outputs.  The 750 volt output powers the original high voltage section, final amp tubes, etc.  The supply has been solid stated.  The 1KV winding runs into a choke input filter (unknown value choke) with a string of electrolytics.  It's all marked 1KV, so I'm going to assume it's 1KV out.  Even if assuming 750, the 811s will really sing (170 watts).  A kilovolt says 250, ICAS.

The audio section is highly modified.  The clipper tube is gone, and the control completely disconnected.  All wires remain, and have been labeled, but the clipper is out.  I didn't see what the two pre amp tubes are, but the driver to the 811s is a 6L6 single ended.  I believe that would have enough scrote, no?

I took some pics, but they are too large, so I'm going to have to reduce, and then I'll upload them.  The case is in good condition, not too much rust and the paint is really good.  Factory rivets in all the sockets except the obviously modified ones.

This will be a work in progress.  I haven't had the inclination to work on a Johnson in 25 years.

--Shane
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KD6VXI
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« Reply #1 on: September 08, 2018, 07:15:52 AM »

More


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KD6VXI
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« Reply #2 on: September 08, 2018, 07:24:09 AM »

I know its a yuuuuuge Longshot, but anyone recognize this one?


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KD6VXI
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« Reply #3 on: September 09, 2018, 02:12:56 AM »

OK.  Put a 3 wire cord on it today, pulled the variac out, and tried to load it up.   Grin

Throw it on 80, twist the dial up to 75, where I had the TS850 sitting, and fired it into the dummy load on spot.

FOUND A SIGNAL!

Long story short, I'm able to load the thing up to 175 watts of carrier and the modulators work!

However, the meter is flaky, which I believe is why it came here in the first place.

The last owner stated he couldn't get any buffer or oscillator current.  I saw it was all the way down so I slightly moved it off the left edge.  Looks good.  Flipped it to TX, got a plate current reading.  As soon as I kicked the xmitter back to standby, the meter stuck on the left side again. 

Is their a common reason for this?  A common fix?

Otherwise, this thing works fairly nicely, although I've only tested 75 am.  Loud and clean modulation, really stout.  The 811As have NO problem 100 pct modulating the 3 x 6146!

--Shane
KD6VXI
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« Reply #4 on: September 10, 2018, 11:46:50 AM »

I guess my question would be, have the T3 and T4 transformers been replaced to match the impedances of the new audio tubes?

My suggestion is to draw a new schematic as is determined by the present circuitry and find out where the differences may be before going further.


Phil - AC0OB
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