I just rebuilt a Ten-Tec Titan 435 that had horrible drift issues on 160
meters. The RF current in the load cap on 160 is very high!
I used strings of 100 pF 3KV CERAMIC disk caps. *No more drift.* Mouser
part number is: 80-c330c101JHG. Replace a 500 pF doorknob with 5 of
these in parallel.
Don't waste your time with doorknobs, they cant handle the current. I
just ripped the original doorknobs out of the Titan 425 and replaced
them with strings of these. 20 second key-downs now no issue on the
Titan 425 on 160 meters.
I would stay below 1.5:1 SWR to keep the voltage down. With high SWR,
the voltage *can be* quite high on the loading caps.
Don't use mica caps either. I tried them. They just blew up.
Some info in the archives of the amps reflector about this subject. Do a
search from contesting.com amps archives. There also some info on W8JI's
site, www.w8ji.com
Email me privately and I can send you some pictures of what I did in the
Titan. I'll try to post the pictures on my photo site later this week
and share the link.
Thanks
73
Jim W7RY
On 3/17/2019 3:31 PM, Gary Smith wrote:
Folks,
I have been having drifting issues on 160
only, not 80M or above, with my late model
SX. I was thinking the 160 toroid
transformers were overheating but the tape
is not brown and I've been assured the bit
of bubbling at the ends is from normal
warming, not excessive heating.
160M & 80M transformers L7 & L5
http://doctorgary.net/toroid-1.jpg
http://doctorgary.net/toroid-2.jpg
Upper band transformer L6
http://doctorgary.net/toroid-3.jpg
I tested the plate caps with my LCR and
all tested as WNL. I cannot do a leak down
test with this LCR meter.
As there's no sign of overheating I can
find anywhere and I haven't been beating
on the amp, I'm assuming the drift is from
the 160M padder caps breaking down over
the years and they should be replaced.
Alpha could have made them easier to
access, they're right underneath the band
switch, screwed to the front RF panel and
the front panel of the RF deck is not
removable (this would have made access a
cinch). The only access to the front area
of the deck is from above and from the
left side.
I did not remove the side panel at this
time, I'll do that when I order & get the
padders. Here's the view of the padders
from above.
100pF band position A
http://doctorgary.net/100pF.jpg
1000pF band position B
http://doctorgary.net/1000pF.jpg
I understand the early models had one 500
pF padder and later models like this one
have two 1000 pF padders in parallel.
The two paralleled 1000pF caps for
band-switch position B are easily
accessible from the side, the two
paralleled 100 padders for Band-switch A
are located deep where I can't get a
screwdriver in to undo them.
For anyone who has replaced these on one
of these amps, have you any suggestions of
how to best get to the 100 pF caps and
remove/replace them with a minimum of
effort?
Also, I'll probably get the HT58 padders
from RF Parts, any other worthy places I
might also check into?
Thanks & 73,
Gary
KA1J
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