Just started to do a refurb of a Heathkit HW16 and stumbled across this circuit breaker wired into the main ac line.



I tried brining it up in a variac and got nothing so am wondering about this device.

I've never seen anything like this. How does it work? How do I know if it isn't working?
I haven't got a clue.

It should have continuity.

It looks like it has a bimetal strip that would heat up and open on over current.

Same idea as a flashing christmas light. A heater (in line with the load) heats up a metal strip, which bends and opens the contacts.

If the current is below some threshold, it doesn't get hot enough to open the contacts.

here is a similar one
https://www.electronicsurplus.com/sylva ... -resetting

I don't think anyone makes these anymore...

I do recall being mystified by that when I assembled my hw-16, I always wonder why they didn't just put a fuse holder on the back panel
in that set. There's probably a story behind that glass CB in there, but that one there is the only set I've ever encountered those.

It is a 3 amp circuit breaker.

Question remains: why not just a 3 amp fuse?

What's cheaper, a fuse holder and a fuse, and an extra punch on the rear side of the chassis, or that circuit breaker.

Not obvious.

Before seeing the answer, I made a guess: a position sensitive switch. Such a thing
would be used in a device using mercury vapor rectifiers to prevent running it
with them not upright.

Because the HW-16 was aimed at the new Novice operator, maybe Heathkit felt a self resetting circuit breaker would be a simple way to protect the transceiver while causing minimal problems for the new operator.

Ten Tec had their own somewhat annoying version of this with their Century 21 CW transceiver which requires cycling the power if you accidentally turn the drive up a tad too far.

Heathkit had largely moved away from fuses to regular circuit breakers by the time the HW-16 was produced with the DX-60A, HP-23A, SB-303, and other updated/revised pieces of ham gear moving to a standard manual reset circuit breaker from the earlier fuse design. I suspect standard circuit breakers were becoming very price competitive with a fuse and holder by that time since they were used in mass production television and other consumer electronics.

Rodger WQ9E

These thermal breakers were cheap and popular 50+ years ago. Not much more expensive than an incandescent bulb. I think Sylvania made them back then.

Much cheaper than a fuse, holder, and the labor to install. We used to figure 25 to 50 cents per hole unless you had a dedicated setup on a press that would punch all chassis openings at the same time.

Rich

https://www.electronicsurplus.com/sylvania-sb618c3r-circuit-breaker-nc-self-resetting?gclid=EAIaIQobChMIhsbgo62y-AIVYm1vBB2g8goDEAQYASABEgIiVfD_BwE

By the time the HW-16 came out virtually all of the decisions made at Heathkit were driven by cost. This clearly explains why they chose this method of protection.

Darrell

Very interesting. Thanks for all the replies. I definitely .earned something new today.

I'm not too impressed with this device and think it would be better to replace it with a current limiter, like a CL90, which I have plenty of. Any opinions?

An inrush limiter is a good addition and I add them to most of the vintage gear that I restore but it isn't a replacement for a fuse or circuit breaker. You still need to provide protection via a fuse or breaker.

Rodger WQ9E

A CL90 is an inrush limiter, not a current limiter. It only has high resistance when first turned on; after that the resistance drops. The higher the current, the lower the resistance; not what you want for circuit protection. There are positive temperature coefficient thermistors that are designed as current limiters. They have to be used carefully since their "trip" current varies with ambient temperature. This is true of fuses also but the PTC thermistors are more temperature sensitive.

If you are "refurbing" an HW-16 then you should have the complete printed copy of the HW-16 assembly manual.
You should also replace the multi capacitor can, the 2 insulated capacitors (special ordered through hayseedhamfest.com),
and replace all of the power supply resistors. You don't need to replace the diodes. I special ordered the 2 insulated
50ufd 400VDC capacitors. I don't mess with the two 67ufd 450VDC radial lead capacitors below the chassis. If you
want you can restuff the original insulated capacitor with the 67ufd 450VDC capacitors which are included in the
HW-16 capacitor kit from hayseedhamfest.com then remount the restuffed insulated capacitors back onto the chassis.
Here's a picture of the 2 special order hayseedhamfest.com 50ufd 450VDC insulated capacitors that replace the original insulated
50ufd 400VDC capacitors.



As others have said, that is a 3 amp circuit breaker. The HW-16 manual assembly manual's part list clearly
states it's a "3-ampere Circuit Breaker" (see picture "33" in the HW-16 manual's part list).

That breaker is in "series" with one of the AC power cord leads. Since the AC power cord can be inserted
into the wall outlet 2 ways, the circuit breaker can be in series with either AC HOT or AC NEUTRAL. You can
check the breaker using an Ohm meter.

Pull the HW-16 power cable from the wall outlet.
Connect an ohm meter across the 3 amp breaker. You should see continuity if the breaker is good.
If you do not see continuity then the breaker is bad, replace it with a fuse holder and a 3 amp fast
blow fuse.

I also replace the original power cord with a 3-wire grounded power cord (recommended).