Neil,
The Argonaut 505 did not have a broadband driver.
It has a tuned circuit that is also tuned by the elevator/pre-selector
control - the top left knob.
You have to tune it for maximum during transmit.
PROBLEM: You also tune that same control to peak the reception. If the
radio is not correctly aligned, the peak for maximum received signal does
not coincide with the peak for max drive power to the final transistor. So
if you peak it for best RX performance, your drive level (and output power)
will be low.
If you did not peak this control during your first attempt on the air, try
again and this time place the radio in TUNE (or key the Morse code key) and
rotate the top left knob while watching the output power.
As I recall, you can read output power directly from the radio's meter.
It may also be that the radio's output transistor is blown. They are very
cheap but the originals are no longer available. You have to substitute the
model.
Here's what you can do.
Wire up a #47 lightbulb to an RCA phono plug , center connection to center
connection and the case of the bulb to the case of the plug. Plug it into
the antenna jack. This makes an excellent dummy load AND output power
indicator at the same time.
Key the TX again and tweak the elevator for max brilliance on the light
bulb.
3w will light it up pretty bright, but not quite full brightness.
Keep us posted.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Neil
Martinsen-Burrell
Sent: Wednesday, February 05, 2014 3:25 PM
To: tentec@contesting.com
Subject: [TenTec] Troubleshooting Argonaut 505 with low output
I went to try my first CW contact last night on the Argonaut 505 that I
bought recently and when I measured the power output, I was surprised at
just how low it was. I measured 2.5 V across the diode detector built into
my dummy load for a power output of between 60 and 130 mW depending on what
I use for the forward voltage drop of the diode. This seems even lower than
it ought to be on this radio and I'd like to troubleshoot and hopefully
repair it.
I have the manual and have been getting familiar with the signal flow and
the voltage measurements in there, but I haven't made any measurements
inside the radio yet. I did make sure that the output was peaked on the
"resonate" control and that the CW drive was adjusted for full output. I
did find that if I turned the CW drive down below a certain level then I
didn't get any voltage reading on the diode detector. The radio receives
well, so I believe that the VFO is working.
I am looking for advice about the general approach to this sort of
troubleshooting. I have an oscilloscope and a DVM and I imagine that I will
be following the signal flow trying to find the block that is not
functioning. Should I start at the beginning of the chain with the
oscillator or at the end with the RF power amplifier board (90195)? Are
there particular components or assemblies that I should be suspicious of on
this radio?
Thanks in advance for any help you can offer.
-Neil KD0UKC
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