Awhile back I asked for help on Titan problem. I finally solve the puzzle.
Thank you all for the many suggestions. Below, a recap of the problem and the
solution.
I purchased a Titan over the internet, hooked it up to my Paragon, and
discovered that it loaded up beautfully but the grid current read zero. How
could this be, 10W in, 500W out, zero grid current? After many fascinating
detours, I discovered the problem: D13 in the power supply was shorted,
causing the B- line to come in at 0 V above ground instead of at 28V. Thus
the cathodes were not biased to cut-off during standby or to AB2 (8V) during
operate. The grid current wasn't really zero. What's measured is the current
through a zener diode, transistor, resistor circuit that pulls the bias down
to 8V from the 28V. No 28V, no current through this circuit, apparent grid
current of zero.
If you're a Titan owner and are trying to follow this, here are some clues.
The bias board doesn't supply the bias, it drops it from the 28V coming in on
the B- line to the 8V. It's a complicated circuit, but just look at Q1, D2,
R19 and forget the rest. The source of the 28V in the power supply is R7.
Again thank you for the many suggestions. The RF choke is staying in. I'm
tuning this thing up as you all advised.
Jon, K6JEK
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