Interestingly enough, the Omni VI+ PA is rated at 100% duty cycle while the
961 power supply is not. I've found that additional cooling on the power
supply is necessary in high duty cycle modes, partly caused by the bridge
rectifier being mounted to the bottom plate for heat dissipation. A small
12V fan blowing on the heat sink in the rear takes care of the problem.
Also, one might take note that if the power supply is sitting flat on the
desk there is little room at the bottom rear for vertical air convection.
If possible, elevate the power supply, allow the heat sink to hang off of
the rear support and allow the heat sink to have more "breathing room".
As to the Omni VI+, I've found that heat build up within the radio does
cause some frequency drift primarily due to BFO frequency changes. I
changed my BFO's to TXCO's and found a nice improvement. All in all,
probably not worth the investment, time and effort, for such a small
benefit.
I've read cases where one removed the speaker, replaced it with a computer
type 12 V fan that made improvements of about the same magnitude to the
radio. This would be a lot less work and a lot less $$.
73
Bob, K4TAX
----- Original Message -----
From: "Chuck Guenther" <ni0c@earthlink.net>
To: <tentec@contesting.com>
Sent: Thursday, July 14, 2005 8:17 PM
Subject: [TenTec] Cooling fans and IF gain
N6KB wrote: "I find that operating my Omni VI in CW contests a fan on the
PA heat
sink is necessary. My Kenwood TS-440 has a built-in fan with temperature
controlled speed, or at least duty cycle. The TS-440 receiver
performance in contest conditions does not compare to the Omni VI
though. I wish Ten-Tec would have included a built in fan. I have never
tried, or thought that I needed, a fan to ventilate the insides of the
Omni VI though."
I used a TS-440S for about seven years (in fact I still have it). The
only time the cooling fan ever came on was during an RTTY contest (I was
running about 60 watts). It never came on when operating CW or SSB.
With the Ten Tec rig, I find the heat sink of my 961 PS always runs at a
higher temperature than the Omni 6 PA heat sink.
Today, in order to alleviate my gain problem, I swapped out the Ten Tec
221 filter for the INRAD 753 (which has a few dB less insertion loss).
The gain seems adequate (and more stable) now, so perhaps my problem was
in the filter, or the connections thereto.
73,
Chuck NI0C
.
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