WTD: HF Dummy Load for servicing
 

I find myself a TV tech, getting dumped on with older HAM rigs for repair
by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one shipped
to Canada, postal V0X 1X0.

Lemmie know if anyone can help :-)

My real email is geek at scorpiorising dot ca

Thanks all,

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

"Gregg" wrote in message
news:La8Ic.32613$eO.22466@edtnps89...
I find myself a TV tech, getting dumped on with older HAM rigs for repair
by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one shipped
to Canada, postal V0X 1X0.


Outside of the usual ones on e-bay , as long as it is a tube transmitter you
can use a 100 watt lightbulb. While it is not a very good 50 ohm load the
tuning of a transmitter should let it work.

I find myself a TV tech, getting dumped on with older HAM rigs for repair
by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one shipped
to Canada, postal V0X 1X0.
=======================
Assuming that the HAM rigs you get for repair are for the HF bands (up to
29.7 MHz) and this being a radio homebrew NG ,may I suggest you make such a
dummy load yourself.

Ingredients :
- 20 pcs 1KOhm-2W - 5% carbon- or metal-film resistors
- 1 pce Cacoa (all metal) circular tin or similar for example a paint
tin.
- 2 pcs Jam jar lid having a diameter slightly less than the opening of
the tin .
- 1 pce SO-239 socket with square flange and 4 holes ( + 2 suitable
screws/nuts/seal washers) to suit PL-259 coax connector
- 1pce 150 mm (6inch) long thick copper wire ,dia 1 to 2 mm ( not
critical)
- 2 pcs Metal stand-off each having 2 tapped ends with screws ( length 25-
50 mm).

a) Drill 20 one mm holes (equally spaced) near the edge of both jam jar
lids and tin area around the holes on both sides.
b) Drill a concentric hole ( 16 mm diameter) in one of the jam jar lids and
a concentric 2mm dia hole in the other
c) Drill 2 pcs diametrically opposed 3mm dia hole in the lid with the 16mm
hole using the SO-239 socket flange as a template.
d) Drill 1 concentric 16 mm dia hole in tin lid and after that use the
SO-239 socket flange as a template to drill 4 holes (dia 3mm)in the tin lid
e) Fit the 2 stand-offs to 2 diametrically opposed holes in the jam jar lid
with the 16 mm concentric hole with the lid's inside surface towards the
stand-offs.
f) Cut resistors' wire ends leaving approx 5mm on both ends
h) Protrude remaining resistor wire ends through tinned holes in lid with
fitted stand-offs and solder.
i) Do the same with the other jam jar lid (the one with the 2mm dia
concentric hole) by pointing the lid's usual top towards the resistors and
solder these to usual inside of lid . The 20 resistors are now sandwiched
between the 2 jam jar lids .
j) Solder one end of the thick 6 inch long copper wire to the SO-239
connector and fit this connector with 2 diametrically opposed
bolts/nuts/washer to the tin lid
k) Protrude other end of 6inch long copper wire through concentric holes in
resistor package and fit the 2 stand-offs to the 2 remaining holes in SO-239
connector flange.
l) Finally solder copper wire to now bottom jam jar lid and cut-off excess
wire.

By putting the package inside the tin you now have a 40 Watts dummy load
It should be obvious that the resistor package must not make direct contact
with the tin.

You can increase the power rating of the dummy load by filling the tin with
oil . I have used motor oil for the past 18 years in a particular dummy load
with the resistance changing from 49.8 to 50.6 Ohms over that time.

However before using oil I would recommend sealing the tin's seams with
epoxy glue ( the 2 components stuff) on the inside to prevent 'oil sweating
' through the seams.

With all the ingredients and required tools available ,the above should be a
1 evening's job.

Measured SWR ( with MFJ 259B antenna analyser) is 1: 1.2 @ 29.7 MHz and
less at lower frequencies.

Although it is unlikely you will be testing the transmitters at full output
for any length of time ,the above dummy load will happily absorb 100 Watts
for 15 minutes if accommodated in a tin of not less than 1 litre (about 1
quarter US gallon)

Good Luck with this simple homebrew project.

Frank GM0CSZ / KN6WH

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

Gregg-

Take a look at http://www.mfjenterprises.com/produc...rodid=MFJ-260C for a
dummy load that will withstand 300 watts for 30 seconds, or 25 watts
continuosly.

It costs about twice what you mentioned, but is less than similar Bird models.
If price is important, search E-Bay for dummy (load,antenna).

73, Fred, K4DII

Gregg wrote:
I find myself a TV tech, getting dumped on with older HAM rigs for repair
by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one shipped
to Canada, postal V0X 1X0.

Lemmie know if anyone can help :-)

My real email is geek at scorpiorising dot ca

Thanks all,

What you want is the Heath 'Cantenna'. These show up on ebay
from time to time. Back in the 60's 70's, and 80's almost every
ham had one so they are not very rare. They do have a small
problem, the brass bands that attach the resistor element to the
unit break in half after many years of use (either from metal
fatigue or chemical reaction to the 'oil') and will have to be
replaced. Small hose clamps may work, or you will have to make
your own from sheet brass. Also many of these were filled with
'transformer oil' obtained from the local power company. While
this stuff had ideal thermal and electrial properties for the
job, it was a hazardous chemical that shouldn't be allowed to
get on the skin, or disposed of to seek into the ground water
table. (CANCEROUS!).

An equivalent to the Cantenna is still being sold by MFJ Enterprises.

Behold, Ralph Mowery signalled from keyed 4-1000A filament:


"Gregg" wrote in message
news:La8Ic.32613$eO.22466@edtnps89...
I find myself a TV tech, getting dumped on with older HAM rigs for
repair by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align
the transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one
shipped to Canada, postal V0X 1X0.


Outside of the usual ones on e-bay , as long as it is a tube transmitter
you can use a 100 watt lightbulb. While it is not a very good 50 ohm
load the tuning of a transmitter should let it work.

That's what I ended up using after I boiled the water in my
immersion-cooled 47R/2W resistor, but didn't know if that was sufficient
;-)

Thanks.

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

Behold, Ken Scharf signalled from keyed 4-1000A filament:

Gregg wrote:
I find myself a TV tech, getting dumped on with older HAM rigs for
repair by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align
the transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one
shipped to Canada, postal V0X 1X0.

Lemmie know if anyone can help :-)

My real email is geek at scorpiorising dot ca

Thanks all,

What you want is the Heath 'Cantenna'. These show up on ebay from time
to time. Back in the 60's 70's, and 80's almost every ham had one so
they are not very rare. They do have a small problem, the brass bands
that attach the resistor element to the unit break in half after many
years of use (either from metal fatigue or chemical reaction to the
'oil') and will have to be replaced. Small hose clamps may work, or you
will have to make your own from sheet brass. Also many of these were
filled with 'transformer oil' obtained from the local power company.
While this stuff had ideal thermal and electrial properties for the job,
it was a hazardous chemical that shouldn't be allowed to get on the
skin, or disposed of to seek into the ground water table. (CANCEROUS!).

An equivalent to the Cantenna is still being sold by MFJ Enterprises.

I had one of those! :-)

I used Shell Turbine Oil instead of the PCB stuff. Blew it on a 4KW 11M
linear a friend brought from Holland :-(

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

Behold, Fred McKenzie signalled from keyed 4-1000A filament:

I am in need of a decent 50 or 100 watt dummy load to properly align
the transmitters at full power.

Gregg-

Take a look at
http://www.mfjenterprises.com/produc...rodid=MFJ-260C for a dummy
load that will withstand 300 watts for 30 seconds, or 25 watts
continuosly.

It costs about twice what you mentioned, but is less than similar Bird
models. If price is important, search E-Bay for dummy (load,antenna).

73, Fred, K4DII

Hi Fred,

I think I'll go the ebay route.

If I get paid before finding it on Ebay, I'll take the DIY advice here ;-)

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

Behold, Highland Ham signalled from keyed 4-1000A filament:

I find myself a TV tech, getting dumped on with older HAM rigs for
repair by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align
the transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one
shipped to Canada, postal V0X 1X0.
=======================
Assuming that the HAM rigs you get for repair are for the HF bands (up
to 29.7 MHz) and this being a radio homebrew NG ,may I suggest you make
such a dummy load yourself.

Thank you!

Aye, I sure can DIY and have done those, but I was very lazy this time and
just took a boo for one that might be available ;-)

I like yours and Fred's ebay suggestion best and will go with one of
those.

Thank you all for your replies!

Take care,

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

hi gregg,

check ebay, do search on decibel dummy and you will
find many nice 100w units n connector removed from
cell service, about $ 10 usd + up.

regards,

gregg

Gregg wrote:

I find myself a TV tech, getting dumped on with older HAM rigs for repair
by newbie licenced HAM's with no vacuum tube experience.

I am in need of a decent 50 or 100 watt dummy load to properly align the
transmitters at full power.

I have stuff for trade or am willing to pay up to $20/USD for one shipped
to Canada, postal V0X 1X0.

Lemmie know if anyone can help :-)

My real email is geek at scorpiorising dot ca

Thanks all,

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca