[Swan] Question

[Robert Balonis]

Hi Dave

The PSU-3A was is the power supply that has the same physical cabinet 
appearance as the 700S transceiver.  There is also a PSU-3, but it's 
cabinet design is similar to that of the 117XC power supply, which 
matches the 700CX transceiver in appearance.  The internal electronics 
components layout of either of those two PSU units is different from 
the 117XC in that it doesn't use the "black box" 117X configuration 
packaged within the cabinet.  However, I believe the circuit design, 
output voltages and current capabilities are near identical to the 
previous 117X/C power supplies, so the RF power output should not be a 
function of the power supply, regardless of which power supply is used.

I think the 700C is rated at 550 and 350 W (SSB and CW respectively), 
so if properly aligned and in good condition, the maximum expected 
outputs should be in the  330 W and 210 W (assuming 60% efficiency at 
best).  The Swan transceiver model number does not necessarily 
correspond to power rating - in some cases the rating was greater 
(350/C) and in some cases lower.  Note that the 700C uses 6LQ6 finals, 
whereas the 700CX uses 8950 tubes, with a rated dc input of 700 and 400 
W.

So, the 180 CW is quite reasonable, although the SSB is lower than I'd 
expect given the CW power output - if possible, it would be nice to 
monitor the output with a scope to do at least a qualitative check to 
insured that the SSB peak(s) are indeed the same amplitude as the CW 
signal to confirm the wattmeter's readings.  I'm not familiar with the 
Bird wattmeter, but a complicating factor with any wattmeter is 
measurement accuracy - Assuming a wattmeter has a 5% FS reading 
accuracy and a 500 W range is used, then the measurement has a +/- 25 
Watts error range.  Worse yet, any measurement error will not 
necessarily be consistent/linear between modes (e.g. CW/SSB) and with 
changes of frequency (e.g. 20 M/40 M) - so its possible for the meter 
to be operating perfectly within specs and to show a reading 25 W too 
high on CW and 25 W too low on SSB (or between two bands), a 50 W 
difference!  If the measurement is not taken with a 50 ohm dummy load 
(other than a SWR = 1::1), the reading will also be erroneously high 
due to the reflected power component - that error is progressively 
larger as SWR increases.

Note that the output on the higher bands, especially 10 meter, can be 
appreciable less than what is achieved on the lower bands, even when 
everything is properly aligned and in good condition.

Regards, Bob  NB3W

On Aug 25, 2006, at 3:38 PM, Dave Meitzen wrote:

> What power supply was paired with the SWAN 700 S transceiver. I am 
> using a
> CX-117 and it seems the max power out is around 180 watts key down -- 
> same
> in SSB on a peak reading Bird. I expected more. I tested two different 
> sets
> of finals with the same results. Power supply has been rebuilt.
>
> Thanks
> Dave
>
>
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