[TenTec] Troubleshooting Argonaut 505 with low output

Steve Mercure w5en at hotmail.com
Fri Feb 7 12:18:01 EST 2014

Good Post!
73 de W5EN Steve
> From: Rick at DJ0IP.de
> To: tentec at contesting.com
> Date: Wed, 5 Feb 2014 17:48:59 +0100
> Subject: Re: [TenTec] Troubleshooting Argonaut 505 with low output
> 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 at contesting.com] On Behalf Of Neil
> Martinsen-Burrell
> Sent: Wednesday, February 05, 2014 3:25 PM
> To: tentec at 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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