With thanks to Frank at DNJ Radio in the United States and to Eric Klein from Klein Communications in West Virginia below are some platinum nuggets when it comes to the AT6666 and what makes it tick so to speak! Massive thanks to both Frank and Eric for the permission to add it here! Remember without radio people sending stuff there is nothing much happening here!
#1: The AM modulation level was factory set to only about 80% and I
was able to figure-out which trim-pot controlled that percentage (and
in which direction to turn it) and was able to increase it to about
~98% AM modulation.!
#2: The maximum AM mode “dead-key” watts (aka: no modulation) when
the front power-knob was set fully clock-wise, was factory set to
about 15 watts, which leads to an excess amount of “waste-heat”
dissipation even before any modulation is added 😦
I then figured-out which internal trim-pot controlled the maximum AM
dead-key (and in which direction to turn it) to lower the maximum AM
dead-key (with the front-panel control all the way up) to about 10
watts, which is a much more “reasonable” level to help reduce the
temperature of the unit, and thereby help to increase the
“service-life” of the RF output transistors.
That then made the low AM dead-key about 1.5 watts (with the
front-panel control turned all the way down), which then makes it much
more “suitable” for situations where someone would want to “drive” a
“linear-amplifier”, with minimizing the possibility of “over-driving”
#3: The maximum FM mode “carrier-level” watts when the front
power-knob was set fully clock-wise, was factory set to about 45
watts, which leads to an EXTREME amount of “waste-heat” dissipation.!
I then figured-out which trim-pot controlled the maximum FM
carrier-level (and in which direction to turn it) and was able to
lower the maximum FM carrier-level to 20 watts, which is much more
than enough for typical FM transmissions., and thereby also helps to
increase the “service-life” of the RF output transistors.
#4: The maximum SSB power output was factory set to about 65 watts
(front power knob turned all the way up), and then figured-out which
internal trim-pot to controlled it (and in which direction to turn it)
in order to reduce the maximum SSB output to about 45 watt (again,
much more “reasonable” for the type and size of the RF output final
transistors in this radio).
#5: The “Echo-time-delay” and the “Echo-level” (aka: intensity) was
factory set much too high (I would sound like I was in a very long and
deep cave), found the correct two (2) internal trim-pots (and in which
direction to turn them) so that now the “Echo-effect” was much more
pleasant (easy to understand) level of sounding like I am in a
“basement Jazz-club”.! 🙂
#5A: I also took a close-up photo of the radio’s interior (attached
to this letter) and circled & marked the trim-pots to go along with
the above changes I made to increase its performance AND longevity of
#5B: I’ve attached two (2) files (pdf & jpg) to this letter which
includes most of the above information for your own use., and so that
you may share it with others if / when needed.
#6: Also, the factory-stock “hand-microphone” has some VERY good AND
“clear” sounding transmit audio (better than I thought it would
be.!)., which was verified by a number of my local friends & customers
when I was testing it on-the-air last evening.!
#6A: So, after disassembling the hand-mic and the cable-end
connector, I was able to create a schematic, by using a simplified
“CAD” program I have.
#6B: I’ve also attached a copy that schematic (in jpg form) to this
letter for your own use., and to “share” with others if / when needed.
7: The main internal oscillator (which is most important when using
the SSB mode) is VERY stable (better than the factory-specs.!) and was
tested / proved-out by using my brand-new Icom IC-7300 as a
“reference” to check the accuracy of the AT-6666 frequency.
When the AT-6666 is transmitting (in SSB mode) it is virtually
“dead-on” with the receiver in my Icom 7300.!
7A: But., when the AT-6666 is receiving from my Icom 7300, the
“clarifier” knob on the AT-6666 must be set slightly to the
right-of-center, at about the 1:00 position 😦
I studied VERY closely the schematics for both the AT-5555 and the
SR-955 (both of which are VERY similar in circuit “architecture” to
the AT-6666, but found no way to even attempt to correct that
8: By way of the circuitry design., the receiver “clarifier” appears
to only be “software-adjustable” by way of the mini-USB port (at the
rear of the radio) and having the proper “service-software”.
Such software would be different from the regular “user-software”
distributed for the AT-5555 and the SR-955, which only makes changes
to “user-channels” and “user-settings”.
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