[TenTec] Omni C and Corsair II Drift

[Robert L Stolzle]

Hi again everyone,

Seems like quite a few of the list members are very interested in the
Omni C and
the problems I mentioned about the one I have so I will try to answer all
questions 
and make comment here to the list.  Probably more are interested that
didn't e-mail
me direct.

First I would like to clarify my last post to the list. I did't mean to
say that the Corsair II
is a better rig than the Omni VI. I ment of the two rigs I have, C II and
Omni C, the C II
is probably the better rig but I like the Omni C better for reasons
mentioned.

A comment was made that these rigs need care and YES,  CARE is the word.
With
proper care they can be a pleasure to use. I have friends that have Omni
D's and C's
and they don't have any  problem with the PTO mechanism. I have found
that the main
tuning mechanism is very fragile and should not be bumped, pushed or
pulled on
with any great pressure such as installing the dial skirt. Just handle it
tenderly .

Had questions about the drift and temperature compensating. I have tried
a few 
NPO 1500 temp comp caps in the Corsair II using an old PTO just for
experimenting.
(Since the PTO is very easy to take out of the C II) With no temp comp
cap it drifted 
down about 350 cps the first hour and then about 200 cps per hour after
that. (only
about a 5 minute warmup) I added a 5 pf temp comp cap and this almost
done the
trick. It drifted up about 100cps the first hour and then stabilized down
for the next hour
and after 2 or 3 hours it only drifted down about 100 cps per hour. So I
decided to try
a 7 pf. This caused a big change.. drifted up about 350 cps the first
hour and then
stabilized  for a 2 hours but didn't check it any longer. This may be
what I need 
but don't like that fast up drift at first. (Ten Tec calls for a 30
minute warm up).
Here is a tip if you try this yourself. Be sure to let the PTO cool off
after soldering
in a new capacitor for at least a couple hours else this can cause false
indications
since the cap is still warm from soldering.

Had a question about an Omni C drifting up for a while and then going
down. What
to do?  Well, I don't really know but it may have too large a value comp
cap or the 
wrong type. Also, and I have a question here, There is bees wax coating
some of
the parts in these PTOs. Could it be that the bees wax is sort of an
insulation to
keep the the temperature from having a faster effect on the capacitors??
If this
be the case then, bees wax on the newly installed temp comp cap will slow
down
that upward drift and allow the rest of the pto to warm up and catch up
thereby 
canceling out the upward drift (hopefully at the same rate).  I am going
to try the bees
wax on the 7pf and see if this helps that fast upward drift. It makes
sense to me since
larger components take longer to warm up than smaller components. Maybe
the bees
wax will insulate the smaller temp comp cap enough to slow down its
heating.
Hope this works. There must be some reason for the bees wax in the PTO.

Had a question about mods for the Omni C. I don't know of any thing that
needs
changing either. A 1.8 khz IF filter is all I have, performance is good
enough.  

This is long enough. I have two questions here. 1. Why the bees wax?? 2.
How
much drift is too much and what kind of stability can we expect out of
the C II, 
Omni C,D?? Someone on this list must know.

Bob,   AC5AM

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