Larry,
Thanks for the positive response to my suggestion to use a TT 961 power supply
(or the AirPAX circuit breakers referenced on their own thread). I've also seen
VSWR diode failure cause the TT 960 PS circuit breaker to trip on my friends
Omni D (my former first TT rig). Garland told my friend to replace the diodes
(1N34s I think) and the rig would stop tripping the PS breaker. It did.
The other suggestions will help reduce RF currents and oscillations but only
timely current limiting can keep the PA from being destroyed by over current
during oscillation or high VSWR.
73,
Gary - AB9M
www.csm-gh.com<http://www.csm-gh.com/>
----- Original Message -----
From: Larry DiGioia<mailto:listacct@longwire.com>
To: Discussion of Ten-Tec Equipment<mailto:tentec@contesting.com>
Sent: Monday, November 28, 2005 6:42 PM
Subject: Re: [TenTec] Comments on "Repairs"
Since you guys were kind enough to give me multiple replies, I am going
to reply to all messages at once:
Robert & Linda McGraw K4TAX wrote:
>Here goes........have patience with my probing.
>
>What type of power supply you using?
>
Astron RM-35M rack mount set to exactly 13.8VDC per another long-time
Omni owner.
>Is the power supply negative connected to the chassis of the Omni via a
>separate ground and not just the negative power lead? It should be.
>
>
Not exactly, but both are connected to a 2" copper ground bus bar using
1" braid, only 2 to 3 feet.
>Is the power supply negative connected to chassis of the power supply? Some
>power supplies {name with held} float the negative and are prone to RF
>getting into the voltage sense circuit and allowing an oscillation to take
>place in the supply. Can spell trouble for the radio.
>
>
Well, I just ran all weekend with my standby Yaesu radio connected to
the same PS. This is also the same PS, set up the same way, that I have
been running since 1998.
>Are all pieces of station equipment connected together back to a common
>point such as the power supply via separate dedicated ground cables.
>Should be.
>
>
All equipment goes (via copper braid or copper strap) to the bus bar,
which is connected via copper strap to a ground rod just outside.
Maximum distance between equipment is maybe 4 feet.
>Regarding the tuner, do you use the radio to adjust the match or do you have
>a bridge like and Autec or MFJ to set the match?
>
>
{The best antenna tuner that money can buy, used incorrectly, is no
better than a cheap tuner.}
The tuners are a Nye Viking and a Palstar BT1500. I use my MFJ tester to
determine whether operation is even possible on bands/antennas, then
tune up again with the radios at 5 watts or so and gradually increase
power. I made a table of all possible bands/settings which I keep on the
wall, and use as a starting point. When it's time to switch bands, I
gradually inch up the power as before, but all that's usually needed are
minor touch-ups.
>Is the meter used to measure SWR in the tuner, or an external meter, or the
>one in the radio. Coax cables between the devices can cause the SWR to look
>good at one place and produce a very poor match at another location in the
>system. This can be due to a bad cable or poor connector installation or
>loose connector on the SO-239.
>
>
I used a Drake external meter for the first 5 years or so with my
home-made tuners, then after switching to the two commercial ones, I use
their internals. There are a few coax switches, though... there are a
couple of 3-foot and a couple of 6-foot "jumpers" altogether, all
commercially-made RG213.
>In my case I use a 238 tuner with its internal SWR/Power meter, a Daiwa
>CN-801 SWR & Power meter, and the SWR meter in the radio. In adjusting the
>tuner I switch in and use an MFJ antenna bridge. Then switch the radio into
>the system. In all cases, with power, all three SWR indicating devices will
>show the same and correct SWR reading. I have seen installations where SWR
>at 3 places will be different. This indicates circulating RF and that can
>give false SWR indications. Hope you don't have this condition.
>
>
Well, with two balanced lines leading into the shack, "circulating RF"
is pretty normal here. But also note, that the last two times this radio
gave out, it was while advancing the power on 20m (coincidence?) and I
barely made it past 10 watts or so when it blew. Once into my Hy-Tower
and another time into a (balanced) dipole.
>Parts for the Omni VI and VI Plus are basically "off the shelf" parts. Be
>assured that Tentec Service is fixing the radio, taking it through a 24 hr
>burn-in and it is working when it gets to you. Hate to say it, but
>something in your station or your method of tune-up is causing a problem.
>
I won't argue that. For a while I thought it was a cheapo coaxial
lightning arrestor (the arc-plug type.) Then I went to having all
suppression outside the house, via Polyphaser for coax and Wireman
spark-plug gadgets for the balanced ones.
I'm with you on the PS issues, but will wait to hear more. Thanks!
Jeff Frank wrote:
>I had a problem with my Omni Six where the radio had to be returned to
TenTec four times and each time something else would go wrong. Eventually, the
radio was fixed and the folks at Tentec remained as helpful as they could be.
After the first two times TenTec paid all the shipping and didn't charge me for
their work.
>
Same here! I do appreciate it, and I know they are trying.
> In my experience they will do the right thing. Don't give up.
>
Thanks for the encouragement! Well, it's kind of self-evident here on
the list: a half-dozen guys who had similar problems, and they are all
still Ten-Tec owners, if not evangelists...
Denton wrote:
> Larry, the same thing happend to my Omni VI.....went back 3 times to
> have both the finals and final driver transistors replaced.
I am pretty sure they never replaced the actual finals, it has always
been smaller components.
> In my case, I was running the rig and another hf rig at the same time
> on a common power supply...on different bands and different antennas.
Not here, although I have a spare rig now, I have never transmitted on
both at the same time.
> Right now, I am running separate power supplies, Ten Tec model 961,
> one per hf rig....otherwise same antenna tuners and same antennas as
> before. So far, fingers crossed.
> I will never be too sure what caused the finals to blow...but I think
> that rf was getting into the final brick via the power supply positive
> lead.
Well, I would be willing to switch power supplies if I thought it would
cure it, but remember, the same one ran it for 5 years with no problem.
Based on what I am hearing, I think I will stock up on more ferrite cord
clamps... but there is already one on the supply lead just outside the
radio.
>Those are the classic symptoms of a parasitic oscillation. You probably
>already know this. But in any case, you need to look at suppression and low
>pass (HF) filters in the rest of the path to see if you can break up the
>oscillation.
>
>73 de Gary, AA2IZ
>
Yes, I agree, but as to the cause, I am lost. I had a low-pass filter
for TVI purposes previously, took it out a while back because we went to
satellite, hmmm, timing is right... thanks.
> Larry....do you notice the same behavior while transmitting into a
> good dummy load or does the problem surface only when transmitting
> thru your tuner into your antenna???
>
> 73, Joe W2KJ
Well, first, I don't own a dummy load, I think they are useful for
tuning "tuneable" transmitters, but on a solid-state final, I don't see
it. As for "the problem surfacing," when it does, I am dead in the water
and the rig goes back to Tennessee, last time it was dimming the lights
on transmit...
>Your PA is drawing too much current for whatever reason. Use a TT 961 PS to
protect the PA or put a similar "fast cycle" 22 Amp breaker in line.
>
>I've been running either an Omni D, Paragon II, Corsair II, or OMNI VI+ for
over 25 years. I always used a matching TT power supply and never had a PA
problem although the PS circuit breaker "popped" many times when I made a
mistake on tune up.
>
This really fits. My present PS is way over-rated at 35A, so I am going
to seriously consider this. Thanks!
Lyle Dunlap wrote:
>Your getting some good advice Gary I would just add a couple of things. Get
>a 20 AMP Air Pax ckt bkr. years ago one could get them from TT but maybe not
>today.
>
>
I would love to find one, I will keep this in mind if I don't go with
the 961.
>Another thing if you do not use some device such as an ant. analyzer then at
>least tune up on a duty cycle. IE: a keyer on fast dits, if nothing else.
>I hear a lot of steady key down tuning these days, even tubes dont like
>that.
>
>
I already made a resolution to do this after getting the new tuners. The
Nye will not tolerate it, the metering is very strange, it has some kind
of a delay in it.
>That fast acting ckt bkr will keep you out of trouble even if you dont know
>what your doing. Not to imply you dont.
>
No offense taken. When chasing DX I sometimes get emotional and
heavy-handed. I also should mention that I run PSK. When I can. But I
was always remembering the ads for the Omni, talking about how the final
would "automatically fold back the power when necessary," and for years,
it did.
>I've had similar experiences (current jumping up all of a sudden because of
>self-oscillation) with the older Ten-Tec radios. In my case the trouble was
>caused by the rig's not producing ALC voltage because of bad diodes. I
>called Garland and he said something like, "Yep, they can do that if the
>diodes are bad." It cost me about $0.96 to make the repair.
>
>73, Mike N4NT
>
That's what they replaced last time. But for me, when it happens, it
self-destructs and never "comes back."
--
Larry N8KU
w w w . l o n g w i r e . c o m
100% CW 100% HF
_______________________________________________
TenTec mailing list
TenTec@contesting.com<mailto:TenTec@contesting.com>
http://lists.contesting.com/mailman/listinfo/tentec<http://lists.contesting.com/mailman/listinfo/tentec>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|