On May 18, 2010, at 12:49 AM, Stuart Rohre wrote:
I have one, but the topic of the 505 had a lot of helful posts to
QRP-L
back in the 90's. I would suggest you search the list archives
available from QRP-ARCI club website. Most everything is there you
might need.
I can summarize the mods to the similar 509 and their reasons, with a
few additional notes.
The easiest mod is to replace the meter lamp with an exact replacement
LED. Based on a recomendation here, I bought it from
superbrightleds.com.
It does have a minor problem of being bright white, while the dial
lamps stay a dull red. I've discussed this with superbrightleds
support and while they don't have a direct replacement for the grain
of wheat bulbs under the dial, they have something similar. It
requires the addition of a dropping resistor.
I have not yet received the LEDs and don't have the resistor, so it
may be a while before I change them.
Another mod to the 509 addressed sensitivity. There have been claims
that it did not have enough on most bands, and too much on 40m. I
guess it depends upon where you are, it could use another 10db or so
to fish those signals out of the noise, but 40m overload is not a
problem here. The fix was to replace the dualgate mosfet in the front
end with a 3n211, and add a switchable antenuator for 40m.
I've done neither. I figure if I need a "better" receiver to hear a
signal, I probably need more than 2w SSB to work them.
The calibration on the dial is not very accurate. Ten Tec says that
the slide rule dial is to tell you which 100kHz segment you are in,
and the tuning dial it self for finer resolution. I have noticed there
is a slight difference in mine in the various band segments. The mods
suggest adding a crystal calibrator. I have the matching TenTec one,
which is external. For example on mine, 14.100 is not at exactly the
same place on the tuning dial as 14.200, the next time around.
IMHO it's fine, except if you are used to your rig reading in HZ, and
expect it to be 100% accurate. It's possible with a modern rig, not a
1970's vintage one.
Connectors are a problem. TenTec used RCA plugs for the antenna, power
in and aux power out jacks. This can be a disaster of you plug the
wrong plug in the wrong jack. Many people replaced them with more
common power jacks, and the antenna jack with an so-239 or BNC jack.
There are also various keying mods for CW, and some voltage regulation
mods to improve SSB transmission.
And the most daring mod of all, someone replace the slide rule dial
with a digital display, making it an Argo 509D.
You can see a lot about these rigs and how they perform with a little
searching on YouTube.
73,
Geoff.
--
geoffrey mendelson N3OWJ/4X1GM
Jerusalem Israel geoffreymendelson@gmail.com
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge
or understanding, as in he has a sub-wikipedia understanding of the
situation. i.e possessing less facts or information than can be found
in the Wikipedia.
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