{"id":6448,"date":"2011-09-21T09:55:00","date_gmt":"2011-09-20T23:55:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2011\/09\/21\/mike-kl7rs-hw-8-dsb-mod\/"},"modified":"2025-07-21T21:00:59","modified_gmt":"2025-07-21T11:00:59","slug":"mike-kl7rs-hw-8-dsb-mod","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2011\/09\/21\/mike-kl7rs-hw-8-dsb-mod\/","title":{"rendered":"Mike, KL7R’s HW-8 DSB Mod"},"content":{"rendered":"

\"\"<\/a>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: <\/span>
http:\/\/kl7r.ham-radio.ch\/hw8\/hw8story.html<\/a><\/p>\n

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!<\/span><\/p>\n

Here’s the e-mail exchange: <\/span><\/span> <\/p>\n

\n
\n
\n

Re: [QRP-L] WA3WSJ Heathkit HW-8 Rebuild Status<\/span><\/h1>\n
Monday, September 19, 2011 7:32 AM<\/nobr><\/div>\n<\/p><\/div>\n<\/div>\n
\n
\n
From: <\/div>\n
\n
“Nick-WA5BDU” <\/nick-wa5bdu@suddenlink.net><\/span><\/div>\n<\/p><\/div>\n<\/p><\/div>\n
\n
To: <\/div>\n
“Bill Meara” <\/n2cqr@yahoo.com><\/div>\n<\/div>\n
\n
Cc: <\/div>\n
qrp-l@mailman.qth.net, sigcom@juno.cm<\/div>\n<\/div>\n<\/div>\n<\/div>\n

I had the same thought regarding amplifier class, and Steve, WB6TNL also emailed the same observation.<\/p>\n

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?<\/p>\n

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?<\/p>\n

72-<\/p>\n

Nick, WA5BDU<\/p>\n

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<\/p>\n

— On Sun, 9\/18\/11, Nick-WA5BDU <\/nick-wa5bdu@suddenlink.net><\/a><\/i><\/b> wrote:<\/p>\n

From: Nick-WA5BDU <\/nick-wa5bdu@suddenlink.net><\/a>
Subject: Re: [QRP-L] WA3WSJ Heathkit HW-8 Rebuild Status
To: qrp-l@mailman.qth.net<\/a>
Date: Sunday, September 18, 2011, 9:44 PM<\/p>\n

Sounds like a great project (or projects!) Ed.<\/p>\n

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.<\/p>\n

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.<\/p>\n

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.<\/p>\n

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.html<\/a><\/p>\n

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!<\/p>\n

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.<\/p>\n

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?<\/p>\n

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.html<\/a><\/p>\n

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!<\/p>\n

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 –<\/p>\n

It uses a LM3900 quad Norton op-amp for the active audio filter, one
stage of audio amplifier, and the sidetone oscillator.<\/p>\n

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”.)<\/p>\n

It has a direct conversion receiver but has a heterodyne frequency
generation system. The product detector is an MC1496 balanced modulator IC.<\/p>\n

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.<\/p>\n

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.<\/p>\n

Bandswitching, covers 80, 40, 20, 15 meters.<\/p>\n

The audio output stage is a small transistor in a common emitter
configuration with a 1k\u2126 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 \u00bc inch phone jack and no speaker.<\/p>\n

Keying is by pulling 12V to ground like in a modern transceiver.There\u2019s
a keying offset of 750 Hz and you tune to the HIGH side to get on frequency.<\/p>\n

Antenna switching is done by a relay with adjustable drop-out time for
semi-QSK.<\/p>\n

Relative power output meter, not used on receive.<\/p>\n

While doing web searches on the HW-8, I came across the web site of
Mike, KL7R (SK), late co-host of Solder Smoke.<\/p>\n

http:\/\/kl7r.ham-radio.ch\/hw8\/hw8story.html<\/a><\/p>\n

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.<\/p>\n

72,<\/p>\n

Nick, WA5BDU<\/p>\n

Our book: “SolderSmoke — Global Adventures in Wireless Electronics”http:\/\/soldersmoke.com\/book.htm<\/a>Our coffee mugs, T-Shirts, bumper stickers: http:\/\/www.cafepress.com\/SolderSmoke<\/a>Our Book Store: http:\/\/astore.amazon.com\/contracross-20<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

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 … Continue reading “Mike, KL7R’s HW-8 DSB Mod”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":6449,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[33,149,15,272],"tags":[],"class_list":["post-6448","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dsb","category-heathkits","category-hw-8","category-kl7r"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/6448","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=6448"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/6448\/revisions"}],"predecessor-version":[{"id":6450,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/6448\/revisions\/6450"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/6449"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=6448"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=6448"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=6448"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}