[TenTec] Omni VI Resistor circuit locations

[Chester]

I would like to add some personal experience to this.

I bought my Omni 6 in 1992 and the darned thing just worked beautiful in
terms of front end overload. I had no test equipment to check IMD, but I
thought I would IMPROVE the IMD (which did not need improvement in the
first place!). 

Being an amateur, I was SURE I could improve on what Ten Tec's engineers
had done, in terms of their selection of 'cheap' pin-diodes. So I
removed the BPF/Front End board, very carefully removed diodes D7
through D30, and replaced each of Ten Tec's 'cheap' pin-diodes with the
more expensive and 'better' (and Mr. Rhode's recommended) HP-5082-3081
pin-diodes. Since the best operating point of the HP diodes occurred
with about 100ma flowing through them, I had to decrease the value of
R14, R15, R25, and R26. Took several hours and very careful soldering,
but I knew it would be better!

WRONG!! Disaster! Seriously degraded the IMD performance and I began to
hear severe front end overload in the presence of strong signals,
especially on 80m and 40m during heavy CW DX contest! Being the smart
amateur I am, I threw away Ten Tec's 'cheap' pin-diodes and thus could
not repair the BPF/Front End board. A replacement board cost $765. I
didn't replace it, just to provide me with a constant reminder to keep
my cotton-picking fingers out of something that was not broken to begin
with!

YMMV!

Tom/W4BQF

Chester Alderman
calderman@cox.net

-----Original Message-----
From: tentec-admin@contesting.com [mailto:tentec-admin@contesting.com]
On Behalf Of Anthony Bowyer
Sent: Wednesday, January 15, 2003 8:30 AM
To: tentec@contesting.com
Subject: [TenTec] Omni VI Resistor circuit locations


An early post by KL7HF concerning the Omni VI 2nd
order IMD mod:

Locate the PBF/Front End Board, and remove. (Bottom
under the shield.) Identify R-14, a 470 ohm resistor
immediately adjacent to connector 24. Remove and
replace with a 220 ohm resistor.
Now - with the board positioned to where the resistor
you just changed is next to you, and with the
connectors 18 and 17 to you left, look for another 470
ohm resistor directly to the left of connector 24.
There will be three others between it and connector
24.
Remove that resistor and replace with a jumper.
That is all there is. The second resistor is not
marked, so is a bit hard to tell you where it is, with
out a picture!
Good Luck.  de KL7HF


Could someone on the list with an Omni VI manual do me
a big favor? I'm trying to find out where R-14 (470
ohm) and the other 470 ohm resistor mentioned above is
in the circuit on the band pass board. I thought it
might be benificial to make this change on an Omni V,
but the part designations and board layout is a bit
different. Of course, it might be different enough on
the V so it can't be done anyway, but thought I'd take
a look. I assume this mod changes the bias on the
switching diodes for the band pass filters.

Any help is greatly appreciated!!!
Anthony



=====
NT4X

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