[TowerTalk] Dummy Load power resistors...questions!

[jimlux]

On 6/28/20 7:32 PM, n0tt1 at juno.com wrote:
> Thanks to Jim and Chuck!
> Definately non-inductive for this application, but the power rating
> is, I don't know.  I know it was used at a 5KW AM radio station for
> some testing.  I should have mentioned that the glass tubes look
> like common florescent tubes....white in color with no hint of carbon,
> etc.  I would do some more examination but I sure don't want to risk
> breaking one of them.  They are now back in their case, sealed by a
> "jillion" screws!!!
> I looked at 
> https://theelectrostore.com/content/datasheets/kanthal_globar_resistors.pdf
> Doesn't appear to be anything similar in appearance, but like Jim said 
> there's
> lots of area for cooling.  It could be that there's something inside the
> tubes which can't been seen.
> Unfortunately I threw away some electronic industrial catalogs from the 
> late 1960's
> era.  Oh! BTW, this dummy load was made by Bendix and it's called a
> "Dummy Load Modulator".  Not sure what the "modulator" reference means.
> I do have photos if anyone wants a look.


probably either an AM transmitter or radar transmitter.

The modulator in a radar transmitter is the thing that generates HV 
pulses of the correct length and voltage.

The modulator in a AM transmitter is an audio amplifier that puts out as 
much audio power as used in the RF.




> 73,
> Charlie, N0TT
> On Sun, 28 Jun 2020 12:01:58 -0700 jimlux <jimlux at earthlink.net 
> <mailto:jimlux at earthlink.net>> writes:
>  > On 6/28/20 11:43 AM, n0tt1 at juno.com <mailto:n0tt1 at juno.com> wrote:
>  > > Hello everyone,
>  > >
>  > > I recently aquired a "commercial" dummy load that I'm sure will
>  > handle
>  > > more than 2kw.
>  > > There are 12, 600-Ohm resistors in parallel that measure 50-Ohms
>  > with a
>  > > Ohmmeter.
>  > > The resistors look like frosted glass tubes with metal end caps.
>  > They
>  > > measure 9.5" in length
>  > > and 1" diameter.  The number stamped on the ends is E9935R and
>  > their
>  > > vintage is late 60's.  A Google search for that exact number
>  > turned up
>  > > nothing.
>  > >
>  > > Question:  Does anyone know the power rating of these resistors
>  > and
>  > > what type of resistor are they?
>  >
>  > They might be non-inductive power resistors from Carborundum corp
>  > (now
>  > part of Sandvik, as I recall). I've got a bunch of them, although
>  > mine
>  > are grey or brown.
>  >
>  > They could also be a thin film resistor deposited on a ceramic
>  > substrate. Same idea - lots of area for cooling.
>  >
>  >
>  >
>  >
>  > >
>  > > I have photos.
>  > >
>  > > 73,
>  > > Charlie, N0TT
>  > >
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