[TenTec] Tentec Omni D no (low) power output

[Rick - DJ0IP / NJ0IP]

Scott, I am replying to Mike's email because he is taking the correct
approach.

Normally, the final stage is driven with about 10 to 12 watts of power
coming from the LLD.
I haven't dug into an OMNI D (mine never broke), but in the old Tritons
which used EXACTLY the same amplifier design, I have.  Like you, I bought
one used with blown finals.
The only thing I don't know is if there are differences in how the LLD
stages and final stages are distributed. However Jack Burchfield once told
me they have used the same amp design for 30 years.  Therefore I believe it
is a safe assumption.

With the Triton, it was easy to unplug the RCA Phono plug of the coax cable
from the LLD to the final amplifier board, and then simply route it to the
Low Pass filter board.  I did that and had an excellent QRP transceiver with
10+ watts out.

It's perhaps a risky assumption, but I assume the Omni D must work the same
way, since it was the rig which immediately followed the Tritons.  Simply
route the output of the LLD through the LPF and you should have yourself a
good working QRP rig.  If it's only 2w, and my assumption above is correct,
then something is wrong.
HOWEVER, even 2 watts applied to the final stage should drive it to 15w or
so.  I BELIEVE YOUR FINAL STAGE IS BROKEN (KAPUTT!).

I have rarely seen blown LLD's.  It is almost always the final transistors.
The #1 reason the final transistors blow out is PEOPLE CANNOT READ.  
The first or second page of the manual clearly states that if you do not use
the original Ten-Tec power supply, then you should insert an 18 Amp circuit
breaker in the D.C. line.  That circuit breaker was the primary protection
for the transistors.  Ignoring that warning was like playing Russian
Roulette with 3 bullets in the gun.

I suspect your final transistors are blown.
It is a lot of work to swap them, but it is not difficult.
The most important thing is to make yourself drawings BEFORE you remove
anything, and then record the order in which you take it apart.  Put it back
together in reverse order.

BEFORE you do that, you need to make sure that my main assumption above is
correct.
To do that, you need the manual for a Triton and for the Omni D.
Simply compare their LLD boards.
You should be able to download the Triton manual from the Ten-Tec archives.

Good luck Scott.

73
Rick, DJ0IP

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Mike Bryce
Sent: Saturday, February 11, 2012 12:07 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Tentec Omni D no (low) power output

Without digging into it deeper, unplug the pa from the driver board and see
if the 2 watts you're seeing is the driver and not the PA. You need to
reroute the driver to the filter board or terminate it with a 50 ohm load
and measure power across the load

mike, wb8vge

On Feb 10, 2012, at 5:51 PM, Scott Sheppard wrote:

> Well, I picked up a real lemon on ebay that I am trying to bring back to
life...at the moment my focus is on teh power output--or lack of it. I
manage about 2 watts or less on all bands and never more than 3.5 amps draw
even with drive full on...so the low level driver is doing its thing anyway.
When I checked at the PA terminals (the feed thru posts to the PA) the
voltages all checked within range so its 'inside the PA...I took it off the
rig and had a look in the hopes something obvious would present itself but
no luck.
> 
> My question is, howw do I go about checking the PA now...can I test the
transistors in circuit? I am hoping it is the 2nd stage of amplification and
not the actual finals themselves as 2 watts is surely just the low level
driver so perhaps its the MRF 476's?
> 
> 73
> 
> scott  VA3IED
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
> 

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