[Johnson] Viking II Problems

[Rich Soennichsen]

Thank you John for the help, this newbie appreciates it.

  Which caps?  I know you probably listed them earlier ('lytics and papers
IIRC) - but did you replace any in the RF section?

Yes, I had to replace some in the RF section, in particular two in a
pi network that is in series with the 6146 plates, they burned up.
Also one in the modulator section which "lit up".
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   Does this mean you have verifiable grid drive, as well as normal
(negative) bias voltage on the grids of the finals?  The. the oscillator,
nulls, and buffer all working? Do you know what the resting modulator
current is?

The grid current, during LV setup, seems to adjust normally with it
dropping to zero as the drive is reduced to zero. The oscillator seems
to also adjust normally.  I have measure -75V at L6 which connects to
one of the 6146 grids.
I don't know what the modulator current is, I mean I don't know WHAT
it is.  :-)  Newbie remember?

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  Are you testing with a dummy load?  If so, do you know it's 'good'?

Good point, I am using a borrowed antenna tuner with built in dummy
load, I will check this.  Perhaps I should switch to a 100w bulb.

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  I had (and again have) this problem with my Valiant.  It is caused by
capacitors in the RF tank that fail under stress can't carry the high
current loads - my symptoms are the same - it's next to impossible to
resonate the plate circuit, (the knob settings are way off normal, roo)
and, even if a dip can be found before it catches fire, the plate current
immediately begins to 'run away' until the "Chernobyl" alarms start
flashing.  ;}   (This is why the Johnson engineers used strings of caps in
seies-parallel - cheaper than one big unit.)

Sounds familiar.

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  Does your II do this on all bands?

I will check.

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  Concerning the plate tank and coupling caps:  even if you check them
'cold', they can still be subject to failure under load.  The only way to
really check 'em out-of-circuit is to use an ESR bridge that has a high
enough output frequency.  Best to just pony up for good micas and then
there's no worries.

OK, good advice.

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Some things I have observed this morning:

R13 is the HV bleeder resistor and it forms a divider giving a voltage
to the clamper circuit.  I am getting strange resistance readings
here, they seem to vary.  It bleeds the HV ok but perhaps it is
failing.
R30 is the other clamper adjustment.  It is turned all the way CCW
pending proper adjustment.
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Thanks again to all for the help

73

Rich