[Heath] Heath AR-3

[ChrisIwata at aol.com]

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.
 
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. 
 
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!
 
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.
 
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.
 
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.
 
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?!
 
Chris, KL7DM
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In a message dated 1/23/2016 9:36:44 A.M. Pacific Standard Time,  
danyoder.cs at gmail.com writes:

I love those stories. I am so glad hat I belong to a group of  guys that 
have truly inspired me. 



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