Heathkit HW-16 T/R Switching Noise

[Sicnarf1]

Hello. I have "resurrected" an old Heathkit HW-16, and she now works
really well. She has an annoying noise in the speaker when switching
from transmit to receive, and I am wondering if anyone knows of a mod or
a fix for this problem?

Thank you for your time and consideration.




--
Sicnarf1

[philo]

I found this

http://home.comcast.net/~wa3rey/TOM/TrHW-16.htm

[Michael Black]

I thought it was like a receiver and transmitter in a single box, and that
the receiver stayed on at alll times. And while I can't remember why I
think this, I thought the antenna switching was a TR switch, ie a tube
between the output of the transmitter and the receiver, that cuts off when
it sees the full force of the transmitter output.

If that's right, you need to be more specific. If the receiver stays on
at all times, then there is likely to be some sort of noise. You need
to check with users of the transceiver to see what's "normal". If it uses
a TR switch, perhaps the tube is weak, and is acting differently than
intended.

I have no idea, the closest I've been to one is the ads in the magazines.

Michael VE2BVW

[Channel Jumper]

From the Eham web site -

The HW-16 is not a transciever except in name only.
It is a separate transmitter and receiver housed in a single cabinet
which happens to use the same power supply.
Which leads to another note... the HW-16 uses an integral power supply
on the chassis.
You don't need to possess or go looking for one of the HP supplies to
run it.
The HW-16 accomodated a grid-keyed VFO via connectors on the rear panel.
Heathkit recommended the HG-10 VFO, which was "rig ready" for the HW-16,
DX-60 and others. You could also use the older Heath VF-1 VFO (from the
AT-1 transmitter days) after converting it from cathode-keying to
grid-block keying. If you hear a VFO-equipped HW-16 on the air today,
it's almost always going to be one of these two VFO's that are powering
it.
If you get a run-of-the-mill HW-16 today, you've got some work to do in
order to get on the air, and you need to be savvy with electronic
repair, or have a good friend who is.

First, the filter capactitors are almost certainly on the brink of
destruction. You may get some hum in the receiver... you will get a LOT
of hum on the transmitted tone. And, if you keep the rig powered up
without replacing the capacitors right away one will do the Pop'n Smoke
Boogey right in your face. It may take a few hours after powerup, but it
will happen and leave a very oily mess to clean up to say nothing of the
stink and the wife's nagging.

There are three "cans", an aluminum one and two black "cardboard" ones.
The first one to go "POP" is the cardboard one nearest the front panel.
The other paper capacitor will follow in time. So, you've got to replace
these three capacitors as a minimum.

Get the construction manual and do whatever voltage/resistance checks
you can. You'll have some resistors which have changed value and which
must be replaced, any you may find a leaky AC cap here or there.

Of course check the tubes. If you can't check 'em, then do substitution
checks. If you plan on keeping and using the HW-16 you'll need to stock
up on some replacement tubes.

Sidetone. The HW-16 uses the infamous neon relaxation sidetone
oscillator. It growls rather than beep when you key the transmitter...
some rigs more than others. One cure - the one I use - is to snip out
the neon bulb and partially unmute the receiver during transmit. This
allows you to hear your transmitted signal as well. If you want to keep
the thing original, there's a wealth of information on the Web about
Heathkit's idea of a sidetone.

Replacing the filter capacitors should eliminate any hum in your signal,
and it may/may not eliminate the chirp. I would expect a small amount of
chirp in this HW-16's signal anyway. Some HW-16's have more chirp than
others and despite much discussion on the subject I still don't know
exactly why.

There are some modifications on the Internet which claim to eliminate
chirp by powering the oscillator from the receiver's share of the power
supply instead of the higher powered transmit side, and/or using an
0A2/0B2 voltage regulator tube on the power line.

There are a load of mods for this rig. Be careful when using them. I've
tried them all. Some mods don't work at all, others work/don't work and
induce entirely new problems.

No SSB RX due to the CW filter only. The side tone was disgusting. The
neon relaxation oscillator was horrid. It did not have a loading control
in the pi network so impedance matching was limited to 50 ohms.

For modern use there are also several things not so good about it. The
compactron tv sweep tube in the final must be hard to find now. It was
Xtal controlled so you need a VFO for modern use.




--
Channel Jumper

[Bill M]

Channel Jumper wrote:
>
> For modern use there are also several things not so good about it. The
> compactron tv sweep tube in the final must be hard to find now. It was
> Xtal controlled so you need a VFO for modern use.
>
>

Actually the sweep tube is still common and is an easy one to find NOS
in the under $10 category.

As I scaled back on my hamming I was looking for a nice little compact
'boatanchor' and the HW16 fit the bill. The bill, literally! I got it
and an HG10B VFO for $100.

The HW16 was apparently somebody's first attempt at kit building. I'm
sure it didn't work and was just put away since it looked to be in such
nice shape.

I did the 15 to 20 meter conversion successfully, tweaked the sidetone a
bit and have been quite happy with it. Seems to have LESS chirp with
the VFO.

[Scott Dorsey]

Channel Jumper <Channel.Jum...@radiobanter.com> wrote:
>
>From the Eham web site -
>
>The HW-16 is not a transciever except in name only.
>It is a separate transmitter and receiver housed in a single cabinet
>which happens to use the same power supply.

[stuff deleted here]

All this stuff is true, but I am not sure it has any bearing on the orignal
poster's question.

I believe that the T/R switch here is doing two things: muting the received
audio and moving the antenna connection. If the timing between these two
things is not good, there will be a thump. If the muting shifts the DC
offset of some stage (say, because a blocking cap is leaking), there will be
a thump.

I believe that this transceiver thumped somewhat when it was new, so I am
not sure to what extent the issue is misbehaviour vs. perception. But I
would bet a youtube search would find some videos of some other people using
the rig so you can compare the behaviour.

This would be a very fine rig for use on 60M where the crystal control is
not an issue.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Michael Black]

I hadn't realized 60metres had become more than just USB.

Michael

[Scott Dorsey]

It has, but CW operation has to be right on the center of the channel
which limits you to a total of five operating frequencies. So not many
crystals to buy!

[mr.cre...@gmail.com]

Hi - I am refurbishing my original HW-16 (1970), and am very familiar with its operation.

What kind of noise? Static, thump, growling, hissing? Do you hv a recording of this noise?

I agree with Scott Dorsey that some kind of rx/tx timing issue is at fault. When new, however, my rig never thumped. Transition btwn rx and tx was "invisible." The TR switch is a PNP transistor called a "bias switch". Its operating characteristics could have drifted significantly or, the transistor could be failing. The date code on my transistor is 039, indicating 1970, workweek 39. 44 yrs is a long time. You can find replacements on eBay.

Looking at the "bias switch" ckt, there are no electrolytics, just the PNP transistor, resistors, and bypass caps (0.1uF).

I found a discussion thread (http://forums.qrz.com/showthread.php?426910-HW-16-saga-continues-now-going-deep-to-get-it-right/page5) about the transistor replacement as an ECG 102.

Check the RX voltages (key up) on the PCB, around Q1 especially, with a high-impeadance voltmeter. The reference values are on the original Heath schematic. This is important before diddling with replacement parts and such.

Larry, N3CCW, cn87