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

[jimlux]

On 6/29/20 10:33 AM, n0tt1 at juno.com wrote:
> OK, thanks Jim,
> 
> Interesting why Bendix would call this thing (in part) a
> "modulator"...nothing
> in there to modulate a RF signal that I know about....just a high power
> 50-ohm dummy load.
> 

It's a dummy load for a modulator, so the nomenclature might have been 
arranged that way, and along the line, a comma or something got dropped.


that is, it might have been "Dummy Load, Modulator"





> 73,
> Charlie, N0TT
> 
> On Sun, 28 Jun 2020 20:04:01 -0700 jimlux <jimlux at earthlink.net> writes:
>> 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.p
> df
>>> 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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>>
>>
>