The HW-8 rehab project of Ed, WA3WSJ, has led to a nice discussion on QRP-L about the possibility of using the HW-8 as a DSB rig.  Mike, KL7R, did such a mod on his HW-8 many years ago and used it successfully in the field in Alaska.   Read his story here: 
http://kl7r.ham-radio.ch/hw8/hw8story.html
Nick, WA5BDU, and I have been discussing the possible need for an additional mod to put the HW-8's final in linear mode.  The picture above is of Mike's rig, with the finals unbiased.  Check out the scope.  Looks pretty good to me!
Here's the e-mail exchange:             I had the same thought regarding amplifier class, and Steve, WB6TNL     also emailed the same observation. 
   The balanced modulator is inserted between the driver and final     amplifier, which has no fixed bias and has its emitter grounded, so     it's definitely class-C.  I do note that the balanced modulator is     passive and probably has 6dB or more of loss, so you're getting a     pretty good drive reduction.  And Mike said he adjusted the audio     while watching the RF output until there was minimal flat topping on     a scope.  So I wonder if it's possible to keep things fairly linear     if the power is kept quite low?
   At any rate, I love the idea.  Here's Mike in the 70s.  He has an     HW-8 he's familiar with, and he's reading SSDRA.  Going over the     simple DSB generation examples, he thinks -- why not stick this in     the RF train of my HW-8? 
   72- 
   Nick, WA5BDU   
   On 9/19/2011 4:36 AM, Bill Meara wrote:                                             Nick:   I enjoyed               reading about your HW-8 adventure, especially the part               about Mike's work with this rig.  I remember talking to               him about it, and I've since come across some articles               describing similar DSB mods.   One thing that all of these               plans lack, however, is a modification to the PA.  It is               Class C in the HW-8, and would need to be made linear for               DSB service, correct?  73  Bill N2CQR           
             --- On 
Sun, 9/18/11, Nick-WA5BDU                wrote:           
               From: Nick-WA5BDU 
               Subject: Re: [QRP-L] WA3WSJ Heathkit HW-8 Rebuild Status
               To: 
qrp-l@mailman.qth.net               Date: Sunday, September 18, 2011, 9:44 PM             
               Sounds like a great project (or                   projects!) Ed.               
                 I'm working on an HW-8 also. Bought it at a hamfest                   this Spring at a
                 good price, but suspected it might have some issues.                   When I started
                 playing with it I noted that transmit power was down,                   the loading
                 control was stuck, and there was no sound from the                   receiver.               
                 The receiver issue was the most challenging and I                   eventually tracked it
                 to a leaky transistor in the T/R circuit which was                   activating the mute
                 function even when key up. I suspect that the                   transistor's problem may
                 have been due to the lack of a de-spiking diode on the                   T/R relay's coil
                 so I added one.               
                 So far I'm not keen on modifying the rig and am even                   keeping the RCA
                 connector (spent an outrageous $5 for a RCA to BNC                   adapter from Radio
                 Shack). Well, maybe not outrageous, but I'm pretty                   cheap. Other than the
                 diode, I did add a 1A fuse and a reverse polarized                   diode downstream of
                 it for reverse-polarity protection.               
                 After going thoThe HW-8 rehab project of Ed, WA3WSJ, has led to a nice discussion on  QRP-L about the possibility of using the HW-8 as a DSB rig.  Mike, KL7R,  did a mod on his HW-8 many years ago and used it successfully in the  field in Alaska.   Read his story here:
http://kl7r.ham-radio.ch/hw8/hw8story.htmlNick, WA5BDU, and I have been discussing the possible need for an  additional mod to put the HW-8's final in linear mode.  The picture  above is of Mike's rig, with the finals unbiased.  Check out the scope.   Looks pretty good to me!
Here's the e-mail exchange:  ugh most of the alignment procedure (I                   don't have a tool
                 that will reach the bottom coils of the dual-coil                   adjustable inductors),
                 the VFO looks good and the power output seems about                   right.               
                 It was nice that QRP Afield and the Washington Salmon                   Run were going
                 right after I did my repairs, so I was able to make                   ten or so QSOs to
                 try it out. It also reaffirmed the idea that QSOs can                   come pretty easily
                 at 1 or 2 watts out -- you don't need the full                   pentawatt. I had my first
                 QSO with the rig the night before, when it was fitting                   that I worked a
                 guy running a HW-101 who said he also had a HW-8.                   Heath to Heath at
                 random -- what are the odds?               
                 I find that if I buy a used rig and have to work on it                   to get it going,
                 I develop a greater appreciation for it. If the repair                   is successful,
                 that is.
                The HW-8 rehab project of Ed, WA3WSJ, has led to a nice discussion on  QRP-L about the possibility of using the HW-8 as a DSB rig.  Mike, KL7R,  did a mod on his HW-8 many years ago and used it successfully in the  field in Alaska.   Read his story here:
http://kl7r.ham-radio.ch/hw8/hw8story.htmlNick, WA5BDU, and I have been discussing the possible need for an  additional mod to put the HW-8's final in linear mode.  The picture  above is of Mike's rig, with the finals unbiased.  Check out the scope.   Looks pretty good to me!
Here's the e-mail exchange: 
                 The HW-8 has an interesting mixture of modern and                   semi-vintage (70s)
                 features. Some things I found interesting were -               
                 It uses a LM3900 quad Norton op-amp for the active                   audio filter, one
                 stage of audio amplifier, and the sidetone oscillator.               
                 The final amplifier is a 2N4427 with a small heat                   sink. According to the
                 data sheet it is rated for 1W output at 175MHz and has                   GWB of 500MHz.(I
                 assume that's original -- I was sort of surprised it                   wasn't "house marked".)               
                 It has a direct conversion receiver but has a                   heterodyne frequency
                 generation system. The product detector is an MC1496                   balanced modulator IC.               
                 The VFO tunes the same linear scale 250kHz on each                   band, 8.645MHz to
                 8.895MHz with a reduction drive. Pretty state of the                   art for the 70s.               
                 Heath rates power the old way with power /input/ of                   3.5, 3.0, 3.0 and
                 2.5 watts input from 80 through 15.               
                 Bandswitching, covers 80, 40, 20, 15 meters.               
                 The audio output stage is a small transistor in a                   common emitter
                 configuration with a 1kΩ resistor in the collector                   lead.So it can only
                 put out a small amount of AF power and into a high                   impedance (1k)
                 load.Has a mono ¼ inch phone jack and no speaker.               
                 Keying is by pulling 12V to ground like in a modern                   transceiver.There’s
                 a keying offset of 750 Hz and you tune to the HIGH                   side to get on frequency.               
                 Antenna switching is done by a relay with adjustable                   drop-out time for
                 semi-QSK.               
                 Relative power output meter, not used on receive.                              
                 While doing web searches on the HW-8, I came across                   the web site of
                 Mike, KL7R (SK), late co-host of Solder Smoke.                                
http://kl7r.ham-radio.ch/hw8/hw8story.html                                The idea that he put the HW-8 on DSB with such a                   simple mod really
                 impressed me. I think I'm going to fool with some DSB                   stuff in the
                 future, although I'm not sure I'll try it with the                   HW-8.               
                 72,               
                 Nick, WA5BDU               
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