Dummy Load.........

[RolandSWL]

Good morning all,

I inherited a Gonset GSB-100 transmitter a few years back. I have not tried to power it as yet but will bring it up slowly on a variac and check for smoke and excessive current draw.

If it passes the smoke test, I would like to see if it puts out any RF. My problem, I don't have a dummy load. More years ago than I care to remember,
I read that homebrewers often used filament-type light bulbs to load their c.w. transmitters. I have since read that this is not a good idea since the bulbs' filament does not exhibit a stable resistance.

Having said this, can a lightbulb be used as a go-no-go load for a transmitter?
If the Gonset has an issue such as a fried HV transformer, it's going into the trash. I don't think it's cost effective to repair this BA for a measly 60 watts of RF. And no, I would not use it on the air without first a Ham ticket.

What say you?

Thanks, Roland...........

[Bill, KD0HG]

Yes, absolutely you can use a light bulb for your go-no go test.

Bill

[KC2ZFA]

you can also use chemistry !

http://www.lu8jb.com.ar/Dummy_load_Exper..htm

http://www.qsl.net/k5lxp/projects/SaltLoad/SaltLoad.html

[RolandSWL]

I like it!

I have lots of wine bottles,but, they are all full. In the name of science  I guess I will experiment with another aspect of loading.

Thanks, Roland................

[Ed/KB1HYS]

That salt water load is also good for load testing HV DC supplies.  I used one to test the plate supply for my dual 4-400 GG amp.  Worked well.

[AB2EZ]

Question:

Will this dummy load produce gases (particularly poisonous and/or explosive gases) when operating?

Stu

[KC2ZFA]

Hi Stu, I don't think salt water has any resonances below the microwave range.

Question:

Will this dummy load produce gases (particularly poisonous and/or explosive gases) when operating?

Stu

[K5UJ]

Q:  What's food?   
A:  A DL when it's in a microwave oven 

If you have a junk toaster you can pull the heating wire out of it and wrap it on a ceramic insulator and make that a dummy load.

[KL7OF]

Oven broiler element

[K4RT]

you can also use chemistry !

http://www.lu8jb.com.ar/Dummy_load_Exper..htm

http://www.qsl.net/k5lxp/projects/SaltLoad/SaltLoad.html

Roland,

I built a version of the salt water dummy load as a Novice. It worked well. Make sure you tighten the cap sufficiently and occasionally check the level of salt water.

Good luck with your Gonset.

73,
Brad

[W7TFO]

DL methods abound, but a simple lightbulb bypass all the schiznit.

If you have a light meter for your camera, it can read differences in intensity your eyes won't.

73DG

[Ed/KB1HYS]

Question:

Will this dummy load produce gases (particularly poisonous and/or explosive gases) when operating?

Stu

Electrolysis will breakdown the water.  table salt and water will produce Hydrogen (gas) at one electrode and sodium hydroxide (liquid) at the other.  That said, Unless you are running something with a LOT current, or left it running for several days, the amount of each produced would be tiny.

If you use washing soda or vinegar in the water, you will get Hydrogen and Oxygen, but again, in very tiny amounts unless you are pumping lots of electrons through there.

I prefer washing soda, it tends to have the least reaction with electrodes, salt and vingegar seem to eat them away eventually, just like a battery.

[KM1H]

If the Gonset has an issue such as a fried HV transformer, it's going into the trash. I don't think it's cost effective to repair this BA for a measly 60 watts of RF.

You can also send it here in case mine needs parts. They also sound great on AM as its a phasing rig and drive a linear just fine.

Pull both rectifiers out first before ramping the power up. If no groaning the transformer is likely OK but dont try using without replacing all electrolytics and paper caps. That transformer is very fragile.

Carl

[WBear2GCR]

the toaster's nichrome wire comes on mica... no need to remove!

[K5UJ]

Good point.  Why do unneeded work.  Jam the toaster in the on position and run RF into the power cord.  Maybe you can even toast some bread while you test the rig. 

[W1VD]

Just measured the 'garden variety' toaster in the kitchen. Draws 858 watts from a cold start dropping to 835 watts when hot. About 7 amps current draw at 121 volts.

Could always attach the cord to an antenna tuner for a good match 

[kb3ouk]

That works out to about 17 ohms. I would've never thought a toaster drew that much current though, since most of them are using just a little piece of two wire zip cord. But most people aren't running a toaster for more than a few minutes at a time, so not really long enough to get the cord hot.

[WBear2GCR]

check to see if they wire the elements in series or in parallel, guessing parallel... rewire?

                    _-_-bear

[W1VD]

I would've never thought a toaster drew that much current though

When I bought a Kill-A-Watt a few years back I measured everything in the house. The 'standard' Mr. Coffee machine surprised me ... 1000 watts whether its brewing or just keeping the carafe warm. A Thermos now keeps the extra coffee warm.     

[N0WEK]

I would've never thought a toaster drew that much current though

When I bought a Kill-A-Watt a few years back I measured everything in the house. The 'standard' Mr. Coffee machine surprised me ... 1000 watts whether its brewing or just keeping the carafe warm. A Thermos now keeps the extra coffee warm.     

The coffee tastes better too when it's not cooked into roofing tar by that pot!

[The Slab Bacon]

When I bought a Kill-A-Watt a few years back I measured everything in the house. The 'standard' Mr. Coffee machine surprised me ... 1000 watts whether its brewing or just keeping the carafe warm. A Thermos now keeps the extra coffee warm.     

It's quite surprising when you find out what commom household appliances draw!

A couple years back when we has a really bad storm up here. (The leading edge of a hurricane) Our power had been out for 4 or 5 hours allready, and I was on standby generator power. (the genny is permanently installed in the garage with the exhaust piped out through the wall) I had been out in the rain for a couple of hours checking on some of my neighbors and was soaked to the bone. I just wanted some dry clothes and a good hot cup of coffee. I changed clothes and fired off the coffee maker with a big sigh of relief. Since I had the kitchen window open, I could hear the genny's exhaust note very well from the side of the garage. It was quite surprising to hear that 5kW 2 cylinder engine load down from the draw of the coffee maker! It made a definately noticable difference in the exhaust note. (Noticably, way more than my 1/3 Hp sump pump)

[k4kyv]

I use non-inductive "Glo-Bar" resistors in a couple of my DLs.  I have found them to be like any other type of carbon composition resistor in that the measured resistance may vary considerably from nominal, and they tend to be flaky in that the resistance is not always exactly the same when I measure the same resistor from one time to another, hot or cold; I have yet to figure that one out. Surprisingly, I recently acquired a 430-ohm 100w non-inductive wire-wound resistor that shows less reactance (at least at 160m) than does my series-parallel network of glo-bars and other carbon comps, that I use to test my 440-ohm OWL. It also reads the same with the ohmmeter whenever I measure it.

[AB2EZ]

Ed:

Regarding the production of gases... and consistent with what you said

I am assuming that even with an HF AC signal applied across the two rods, one would produce both hydrogen gas and chlorine gas via electrolyis.

If the power going into a 50 ohm dummy load is 100 watts, then the rms current is 1.4 amperes.

The electrolysis process can be viewed as a full wave rectifier. Regardless of polarity, you produce hydrogen at one electrode and chlorine at the other electrode... in proportion to the |current|. Therefore, the average rate of production is proportional to 0.9 x the rms current = 1.3 amperes.

1.3 amperes corresponds to 8 x 10^18 electrons per second.

It takes 2 electrons to convert a pair of H+ ions into a hydrogen molecule. Likewise, one must remove 2 electrons to convert a pair of Cl- ions into a chlorine molecule.

Therefore, with 100 watts going into a 50 ohm dummy load of this type...one is producing 4 x 10^18 molecules of hydrogen gas and chlorine gas each second.

Avogadro's constant is 6.02 x 10^23. Therefore one would be producing 6.6 x 10^-6 moles per second of hydrogen gas and chlorine gas. At room temperature and atmospheric pressure (not necessarily valid for a sealed container) this corresponds to approximately 1.6 x 10^-4 liters per second = 0.6 liters per hour of each gas.

If one used this kind of dummy load with 100 watts of power, infrequently, for a few minutes at a time... and if it were properly vented... the production of hydrogen gas and chlorine gas does not appear to present a problem.

However, I am concerned about what might happen if one ran 100 watts into this dummy load for 1 hour... particularly without proper venting.

Stu

[w1vtp]

We are talking about a transmitter that puts out 100 watts, right?  Why not use the time honored light bulb.   It worked for this guy

http://www.ohio.edu/people/postr/bapix/viking1.htm

I'm a bit concerned about using any sort of load that may emit gases and may hurt people.  Resistive elements that do not come close to a proper load for the transmitter would be another concern of mine.

I highly recommend investing in a proper 50 ohm load that will handle your anticipated needs and a power meter. As far as firing up such a rig after so many years of no use, the usual caution needs to be observed.  Check the power supply filters for any obvious problems - shorts, no apparent capacitance as observed by (preferably an analog) ohm meter.  It might help to remove the HV rectifier and lighting the filaments as a preliminary step.  The HV secondary could be checked at this point.  A word of caution: many current DVMs will not handle the AC voltages across the secondaries of ham transmitters.  I like the older Simpson 260s - example; the series 3 with a 5 KV AC  scale is nice for this test.

[RolandSWL]

Thank you to all who replied to my question.

O.K. so I used the time honored method of bringing up the line voltage with a variac.

First with the two 5U4's out and again with them installed. I took my time with this process though the temptation to give it full line voltage was tempting. No smoke or sparks, just that intoxicating warm tube aroma.

I could not scrounge up a proper dummy load, so instead I used a small chicken band antenna and set the frequency to 29mcs. I kept the drive turned way down and monitored the signal on a portable radio. The signal was very weak and faded out within 5 yards of the xmitter.

I'm thinking (always dangerous) that the 6DQ5 final is toast as I could not get any plate current to register on the meter. I will pull and test all the tubes this weekend.

When it comes to replacement tubes, are there any preferred brands? Any to avoid?

Also, Holy Smokes! this thing has potentially lethal voltages inside! I fried my cheapo multimeter trying to measure the output from the h.v. xformer. At least I know that the large iron thing is still alive and angry.

Thanks again, Roland..............

And yes, I'm studying for my Ham ticket. I'm way too old to go pirate.