[Johnson] Johnson Adventurer question
Ed - K9EW
k9ew57 at gmail.com
Tue Jul 17 17:27:12 EDT 2007
I replaced those 'lytics before turning on my Adventurer last year. I
put two 22mfd 450vdc electrolytics in series for each of the original
capacitors. I used a 2 meg 1/2w equalizing resistor across each of
the new caps. This gives you 11mfd 900vdc replacement caps for the
original 8mfd 700v caps. The 22mfd 450vdc electolytics are available
from Mouser. I used the radial version, but if I were doing it again,
I'd use the axial version for that part because they're easier to work
with.
Hope this helps.
73,
ed - k9ew
On 7/17/07, Weiss <telegrapher at hotmail.com> wrote:
> A few nights ago one of the 8 mfd capacitors in my Johnson Adventurer developed a short. In so doing, it burned the power transformer to a crisp before I could yank the power cord out. In a macabre humor sort of way, just as I grabbed hold of the line cord amidst the thick plume of smoke, the fuse opened (It would have been nice if the fuse had opened a bit earlier to protect the secondary of the transformer but such things don't seem to work that way although you can bet I am adding a fuse to the secondary of the high voltage winding.
>
> Anyway, does anyone know what the original Adventurer power transformer voltages are? Oddly my Adventurer manual is lacking in any voltage information except for the 650 DC it says belongs on the 807 plate. Obviously I realize there is a 5 volt rectifier filament winding and a 6.3 volt filament winding. The RCA Tube Manual states the plates of the 5U4 run "between 350 and 500 volts." I jury-rigged an old TV transformer that creates only 600 volts across its secondary for a 5U4 plate voltage of around 300 volts for each of the rectifier's plates. It is not enough horsepower to pump the Adventurer output up to its previous 28 watts RF output with 110 ma on its 807's plate. I am thinking the original transformer must have been a 800 or possibly 1,000 volt secondary or so. The original transformer is stamped "P2758" but I have been unable to locate anything in any of the online Thordarson or Stancor lookups. It might not even be a Thord or Stancor transformer.
>
> Also, does anyone know where you can find "700 volt" electrolytics these days? 8 mfd at 450 WVDC and even 500 WVDC are easy to find but the 700 volt caps are a challenge.
>
> Thanks for any help.
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