|Page 3 of the Ten Tec Argonaut 505 trouble shooting work being done by me on one of my old second hand argonauts. de..Earl
VE3AB and this is part of www.hamelectronicsmagazine.com ...a free on line ham radio electronics and experimentation web site.
I pay for this site out of my own pocket using funds I generate from selling parts and doing small repairs to basic amateur radio
gear. Ten Tec Argonaut 505, 509 and 515 mainly. But I also work on other rigs including FT301, FT221, Atlas 210x.
60s, 70s and some 1980s rigs and some simpler qrp layouts I can work on. New sophisticated radios I don't work on. I don't think I
could easily get the parts!!! -- I have lots of older solid state parts and I sell a few orders to hams overseas and in North America.
SMALL HANDFUL of parts typically! I cannot compete and don't want to compete with the Bigger suppliers.
I was using my Argonaut 509 and an RF final board that I had modified with transistor sockets to
try out various transistors. Here I try out some MRF237s. They didnt seem to work. NOT ONLY
DID THEY NOT WORK..BUT THEY COMPLETELY FAILED WITH JUST A COUPLE OF SECONDS
ON TRANSMIT. I bought these from China and Im not against China in any way..but I wonder
whats up with these transistors. I tried 2 pair out and very brief transmit test and they failed
completely. 4 MRF237s now toasted and Im not going to be selling the other 6 I bought! I may
just write the whole lot off. March 6th update: after thinking it over....I might try using a 2.2 ohm
emitter lead resistor in each transistor in this circuit. The 515 with its higher gain transistors uses
this resistor and it kept the finals much cooler. I better not blame the transistors or the chinese..at
least not yet!!!
MRF607s, with their 12.5 db gain..seemed to work fairly well and I had some old stock TRW PT
series transistors that seemed to put out power pretty good. -- I am experimenting now with the
various varieties of transistors. I also tried some MRF8004s from Dans Small Parts. NOTE:
Actually..for this repair..I ended up using an MRF607 (new old stock ones) and a couple of MRF
8004s that I bought from Dans. They seem to be working very well. (noted: 3 Mar 2012).
I found out by board swapping that this 505 Argonaut that I had been working on lately..had
both bad final output transistors and a bad driver transistor as well.
Here with my good working 509..I try out different boards and different transistors. The old
vintage 70s transistors were pretty good actually. They seemed to be able to withstand
some abuse. There is NO SWR foldback circuit or other short or open circuit protection with
the Argonauts ..so check and double check your antenna/coax connection before
Even these 2n3053 transistors are same drop in compatible (pin for pin) in the
Final PA circuit boards of ARgonaut 505/509. They may not put out as much power
however. The ones on the left were bought from Dans Small parts and have no
part numbers on them. I want to test these out in my circuitry before I sell them to
anyone. Im going to be building a test jig for RF transmit testing of transistors.
Maybe something like a "little joe" transmitter with sockets for the xsistors.
above pictured the rf pre driver transistor Q2 (dark plastic) in middle. and the driver transistor
with the finned heat sink. Q2 was working (amplifying) but the driver was not. I removed the driver
transistor. This circuit board and parts are shown on the main layout drawing of the argonaut
505. I traced the circuitry and tried to follow the traces under the component side of the board.
It takes a bit of patience and concentration. There is a TEST POINT around Q2 as shown on the
main drawing. With my rig..it was just a 1.5 inch bare wire that I clamped onto with the probe.
I put a piece of yellow heatshrink on it to make it stand out. Its not the easiest board to work on.
You cant just unplug it and flip it around and test and repair the board. It is embedded in a
chassis with mechanical parts around it. The receiver front end DG mosfet can be seen on the
left sid and the transformers are all tuned with ferrite slugs and a moving aluminim plate as the
photos I took show.
Several of these mounting fixtures for the slug tuned cols were loose and I epoxied them back
down to be stable. The tops of the coils with the adjusting screws ..I DID NOT TOUCH..and I
wont touch them ..unless I find they are in bad need of adjustment. The tops of the coils are
sealed with a type of wax. The coils themselves are secured with some expoxy to the aluminum
plate. Some of the coils were physically moving around so I used some epoxy to fasten them in
Right now..I'm just trying to get the rig..up and running..(which I have done now..3 March 2012).
I'm going to be operating the rig for awhile and see what it is like. So far..on 20 meters it is
working very well. Good output..good signals on receive. NO NEED to align this band by the
looks of it. It is not in desperate need of alignment. The PTO is not all that smooth..but it will
do. Just think of the qrpers using crystals and vxos! It is good enough for me the way it is right
now! I tried sending cw and listening to the signal on 10 meters using my FT757GX as a
receiver. The signal sounded good and was reasonably stable. Good enough for now!!!
In amoungst all the circuitry is the pre driver transistor Q2 and its test point. I used yellow
heat shrink over this test point wire. You can also see an electrolytic capacitor. By
now..these older capacitors might need to be changed. It wouldnt be a bad idea to recap the
Argonaut 505 with new electrolytics. I may well do just that..since the rig is being worked on.
I plan to get this rig up and running and use it even though it is not in factory condition.
It works and the only real thing it needs is a CW filter of some sort. I have the NE SCAF kit to
build and then the rig should be good enough to do some basic cw contest work or maybe
use it to operate 10 meter CW when the band is good condition.
What I did with the driver transistor was to replace it. It had an open circuit in one
of the junctions. I fabricated a socket on the top side of the circuit board. I cut
these IC socket headers (shown on the left side of the picture). I made a good
snug transistor socket so I can replace the driver transistor if it ever fails again or if
I want to experiment a bit. The heat sink is one I had in my junkbox.
The original driver a 2n4427. It was damaged. I tested the circuit in transmit mode and the
driver transistor was not amplifying. I took the transistor out and tested its junctions with the
VOM in diode test mode and one of the two junctions was blown open. I ended up using one of
my MRF 607s. I felt it had about 12.5 db gain. This is a bit more than many other types of
transistors which seem to be around 10 db. It worked quite well.
The tip of the red plastic pointer in picture above is the "pre-driver" transistor. It seemed to be
giving some signal amplification. This whole board is a bit difficult to work on. It is not like the
other plug in circuit boards that are out in the open. But I got the probe of the spectrum
analyser in around all the obsticals and made some measurements. To remove the driver
transistor..I could not get my solder sucking gizmo to work in those cramped quarters so I used
solder flux and braid and it was fairly easy.
Above..the 5 slugs on this aluminum plate that moves up and down to tune
the tuned circuits. It actually works quite well. I have never tried an
alignment on this 505 or even the (somewhat simpler) broad banded 509 or
the 515. I do have a couple of sweep generators and I may try tackling this
task. I'll work on my own collection before trying alignments with other
peoples rigs. I'm quite good at tracking down problems and can do some
board level trouble shooting for other people. My $10 per hour bench rate is
a hobby rate and I take on the odd job here and there..Ones that I know I can
get good results with.
The driver transistor on the foil side of the circuit board. I scratched the Emmitter and Base
connections on the circuit board for furthur reference.
|CLICK HERE FOR THE FOURTH PAGE
(next page) in this series concerning the Ten
Tec Argonaut 505. It was the first SSB/CW
radio that Ten Tec developed back in the early
1970s (around 1973 or 1974).
How do I know the older transistors from the mid 70s
can withstand some abuse?? I used to abuse them!!
I operated Field Day with the Argonaut 509 back in
1974. One of my antennas had a 5 to 1 swr and I still
operated the rig into it and it worked fine! NO Swr
protection in these radios. Also..I boo boo a few
times and forgot to plug in the antenna.
I think some of todays transistors are built with the
understanding that they wont be subjected to much
Audio people have bought some of my old Delco
transistors from the 60s and 70s! Maybe they know
something or maybe they just like the old vintage
stuff..or maybe a bit of both.
I had my 509 pictured above on the bench at the
same time. I tried the finals pa transistors out in
this rig as well. And was looking at a few things in
the 509 doing comparison as I went along. The
final pa board is more conviently located at the
rear of the rig in the 509.
|Pictured left.. I have my "final PA (Power Amplifier)"board modified with
transistor sockets. This is so I can try out various different transistors as
Final Output transistors.
These MRF237s did not do so well at all! I have damaged 4 of the 10 I
purchased off ebay. Im going to stop selling them and try and figure out if the
transistors are defective.
Other transistors such as the MRF8004 ( I bought at Dans Small parts) seem
to do well for ruggedness and power output.
The Argonaut 515 has a different PA circuit board which accomodates a
different transistor (the MRF476/2SC2075).
These transistors provide about 17db amplification. With my 515 I get close to
9 watts output on certain frequencies with them.
I plan to either make myself or enlist the services of Far Circuits to
manufacture me some 515 final amp boards. Another board I am interesting
in making or getting FAR to make for me is the Audio Board based on the 509
I may well go to FAR soon (today is July 14th 2012) and get some quotes for
them to make me some of these circuit boards. The FAR circuit boards will be
far more modern and good looking than the old 1970s ten tec boards.
I will try to get extras made up to sell to other Argonaut owners.
|Argonaut 505,509, 515 repairs and restorations. My own 505 is fixed up and now going strong.
This is page 3 of me troubleshooting my old 505.
*** I do some repair work for other people by mail order. The kinds of gear/electronic equipment I
can work on is the older style solid state radios and accessories. My bench rate is only $10 per
hour..which makes it worthwhile to send the piece of gear in the mail for service by me. I dont
work on video, memory/computer circuits, as I dont have the parts and specific knowledge
required to work on those circuits. For "free quote"and opinion on your gear..here is my email
address link to write to me. firstname.lastname@example.org
are two of my sites that are mirror
They have been established in
2005 as a hobby that may evolve
into a small at home one man
73 Earl VE3AB