On Sun, 2009-02-08 at 01:03 -0500, Gary Smith wrote:
Thanks for the suggestions.
I'm not near the amplifier at the moment and can't open the amp to
have a look see but I did bring my manual with me and took a macro of
the the band switching section of the schematic and since I can't
attach it for here, it's on my website.
http://doctorgary.net/Titan425TankSchematic1.jpg
I couldn't see on the photo of the amp just where the padding caps
are. Perhaps the idea of using doorknobs in the amp is not practical
space wise. It seems as the tuner mentioned in the thread might have
more space than the 425's tank?
If there's space in the 425, it seems it might be worthwhile to just
replace all the padding caps with superior versions than are in there
right now. I'd be more than happy to do that. One kind offlist email
suggested amp ratings of at least 2.5 at 1.8MHz. I would prefer to
use something well suited and add in some overkill factor if that's
reasonable, I do want stability and this amplifier is really
excellent other than this one current issue. If I can beef up the
components to make it more bulletproof, I'm for that.
A way to look at the current in the padding capacitors is to realize
that 2Kw at 50 ohms is 316 volts RMS. The reactance of a 220 pf padding
capacitor at 2 MHz is 360 ohms, so the current in that padder would be
nearly 0.9 amps. At 4 MHz, 1.8 amps. Then one needs to allow for the
output voltage being higher, say for feeding 2:1 SWR load, tuned to 100
ohms resistive. 447 volts RMS, 1.25 amps at 2 MHz, 2.5 amps at 4 MHz.
Cornell-Dubilier metal cased mica cap rated at > 20 amps and 1KV should
handle these conditions with no problems.
So based on the above info & the schematic section, which caps might
I be most likely to want to replace and what would be best to replace
them with? I am out of doorknobs except for a couple of fixed vacuum
caps but they're the size of a large doorknob.
Thanks again for the help, I've apparently got this issue narrowed
down quite a bit with everyone's help.
Gary
KA1J
73, Jerry, K0CQ
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