What is this? Broadcast Amplifier Transmitter?.paper weight?

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Lowvolt
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What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Lowvolt » Mon Dec 17, 2018 8:48 pm

I would like to kindly take a moment of time from someone with knowledge of vintage radio broadcast equipment. I buy storage auctions and came across one full of radio broadcast gear tube amps gates harris, ampex, russco etc. I can search and sell those but these amplifiers or whatever they are have no distinguishing maker or model. There are two of them very large and heavy about 24 inches rackmount and 50 or so lbs. any help would be gladly appreciated as this is how i feed my family :) here is a link to some pics : https://imgur.com/a/8jsBBtF

w9wi
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by w9wi » Mon Dec 17, 2018 9:37 pm

"Dummy Load", also known in some countries as an "artificial antenna" which is probably easier to understand.

It would be used while testing a transmitter. If you aren't sure the transmitter is operating properly, it might be transmitting on frequencies other than the one you want it to transmit on. If connected to an antenna, it might interfere with other stations.

But transmitters can be badly damaged if operated without an antenna attached. So, you'd connect the transmitter under test to a "dummy load". The transmitter thinks it's an antenna, but it doesn't radiate any power so it can't interfere with anything.

I expect it's going to be difficult to put a price on these without knowing how much power they can handle. (which would be on the nameplate. I would have expected that to be the flat piece behind the handle in the second photo. )
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Doug Smith W9WI
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Lowvolt
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Lowvolt » Mon Dec 17, 2018 11:30 pm

Hmm? thanks for the reply..dummy load huh?..sounds like a nickname for my dad..lol..so after some research i cant seem to find anything that resembles this as a "dummy load" or artificial antenna especially this large

"edit" I found some by adding the word dielectric into the search. Thanks a bunch for the help.

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Dale H. Cook
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Dale H. Cook » Tue Dec 18, 2018 6:14 am

Note that this dummy is oil-filled, which is typical for units rated 1 -2 kW or less. I think the largest oil-filled dummy I've seen is 2.5 kW, a reject load for a TV transmitter. The type of oil used is critical for heat dissipation at the load's rated maximum. Dow-Corning 200 was used not only in dummy loads but in instruments such as some of HP's power meters. It is no longer made by Dow but is still made as Xiameter PMX-200 silicone fluid.
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Steve Brown
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Steve Brown » Tue Dec 18, 2018 12:36 pm

I'd say it's a 5kw dummy load, as the fans on the bottom reportedly double the continuous power dissipation of a 'regular' 2.5 kW load. Check EBay for the prices, but there are a lot of them out there, because when US television stations converted from analog to digital signals these loads became surplus. If you do sell this dummy load to someone you should make sure to replace the pressure relief cap with a solid cap or the oil will probably spill and contaminate at least the inside of the shipping box.

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Lee_Wheeler
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Lee_Wheeler » Thu Dec 20, 2018 9:09 pm

Since it has the 3 1/8" flange it might be larger. Dielectric shipped those with the output switching option that were used as rejects on a Harris FMD50K. On all three of the 50Ks that I have dealt with the fans failed and they blew up under load.

If they read 50 Ohms with an Ohmmeter then they have value but if they read open or high resistance (measuring between the inside cup and the outside pipe on the flange) then they are just paperweights.

...Lee

Nathaniel Steele
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Re: What is this? Broadcast Amplifier Transmitter?.paper weight?

Post by Nathaniel Steele » Fri Dec 21, 2018 10:13 am

Pictures won't load for me for some reason, but I have a 10KW dummy load that's oil filled with a 3-1/8" flange, and fans. It's good for 5K with the fans off and 10K with them running. Heavy SOB......

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