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<DIV>Some years back I bought a AR-2 (AR-3 precursor) from W8EK on this
list. Cosmetically bad, but electrically and mechanically OK. The
intent was to update the radio to be useful today adding solid-state tubes
(JFETs and MOSFETs are essentially triodes/tetrodes) as modifiers. Thus the
radio would still have tube-like characteristics since the mods could have been
done with tubes instead of FETs.</DIV>
<DIV> </DIV>
<DIV>First impressions: Lots of hum and distorted audio. Plenty of
VFO drift, CW/SSB unusable above 40mtrs. Low sensitivity on higher bands.
Builder was a novice, the radio was a rat's nest. </DIV>
<DIV> </DIV>
<DIV>Replaced the 12BE6 pentagrid with a 12BA7, twice the conversion gain.
Used this stage as a mixer only: Fed with a Vackar MOSFET/JFET VFO, this
provided more even VFO injection at higher freqs for better sensitiviy and
better stability (no heat). Yet still had mechanical instability
since coils are mounted on the band switch instead of to the chassis (who was
the designer of this SNAFU?). The dial markings are not accurate, they
weren't originally either. I added a socket to connect a frequency
counter: You can get one on e-Bay now for $15!</DIV>
<DIV> </DIV>
<DIV>Added a JFET IF stage with a 4-pole ceramic filter. Steeper skirts
for better SSB reception. Used tube AGC for JFET also.
4Khz bandwidth, so still can't reject alternate sideband, but good for AM. 2nd
IF stage really perked up the radio.</DIV>
<DIV> </DIV>
<DIV>Used 6AS6 as combined product-detector for SSB and grid-leak detector for
AM. Fed suppressor grid with JFET BFO using 455Khz ceramic
resonator. This is unique tube. Found circuit in one of Pete
Hawker's books, but the schematic was wrong! Used original diode
detector for AGC only, thus AGC works on SSB as well as AM.</DIV>
<DIV> </DIV>
<DIV>Replaced some Electrolytics. Beefed up the high-voltage filter to both
reduce hum and reduce voltage. Added some high-voltage Zener diodes (0A2 or
0B2 replacements). Most of the tubes were being operated above their
maximum voltage rating (again, who was the designer?)! Added negative
feedback to the audio chain. Now audio is clean and hum-free. Replaced the
5Y3 with a 5W4: This saved 1/2 amp filament current. Added a thermistor to
power transformer input to provide controlled startup, less strain on the
filaments.</DIV>
<DIV> </DIV>
<DIV>Journeys' end: Aside from mechanical instability the radio is
gudenuff to be used today. The big speaker makes SWL enjoyable.
Whatduya expect from a single conversion radio with a 455Khz IF
anyway?!</DIV>
<DIV> </DIV>
<DIV>Chris, KL7DM</DIV>
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<DIV>In a message dated 1/23/2016 9:36:44 A.M. Pacific Standard Time,
danyoder.cs@gmail.com writes:</DIV>
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<DIV dir=ltr>I love those stories. I am so glad hat I belong to a group of
guys that have truly inspired me. </DIV>
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