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Peripherally related...
I have a new-to-me Bird 8890 load.? It's rated VSWR 1.1:1 to 1 GHz, but sweeps substantially worse, rising to nearly 3:1 at 435 MHz.
I've taken the load assembly out of the oil and there's no obvious physical damage.? The load does test 50.02 ohms at DC.
Any suggestions on what to try in order to get this bad boy back online?
Thanks,
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The length of the coax between your dummy load and the test source is likely the culprit.?
Try various lengths of coax.
?
73,
Dave, w6de
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From: [email protected]
<[email protected]> On Behalf Of Scott Townley via groups.io
Sent: 11 June, 2024 20:40
To: [email protected]
Subject: [ham-amplifiers] Bird Termaline load repair
?
Peripherally related...
I have a new-to-me Bird 8890 load.? It's rated VSWR 1.1:1 to 1 GHz, but sweeps substantially worse, rising to nearly 3:1 at 435 MHz.
I've taken the load assembly out of the oil and there's no obvious physical damage.? The load does test 50.02 ohms at DC.
Any suggestions on what to try in order to get this bad boy back online?
Thanks,
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The transition from "N" to the load should be a tapered "constant impedance" section.... not a flat plate which is fine to around 100mhz.
Don Roden?
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On 2024-06-11 3:47 pm, Dave w6de wrote:
The length of the coax between your dummy load and the test source is likely the culprit.? Try various lengths of coax.
?
73,
Dave, w6de
?
?
Peripherally related...
I have a new-to-me Bird 8890 load.? It's rated VSWR 1.1:1 to 1 GHz, but sweeps substantially worse, rising to nearly 3:1 at 435 MHz.
I've taken the load assembly out of the oil and there's no obvious physical damage.? The load does test 50.02 ohms at DC.
Any suggestions on what to try in order to get this bad boy back online?
Thanks,
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It is an "exponentially tapered" section.? I can send a picture of the load assembly if that would help with suggestions.
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Scott, I wonder if the resistor may have been replaced with one from a contaminated load or a water load,
not knowing the history on it makes it a Sherlock Holmes case.?
Measuring near 50 Ohms dc does show it has a good resistive element though.?
There are two types of elements used for load resistors like this, one is a glass rod with the film deposited on it, the second is made of bulk carbon.
I've seen the first type have a contaminated film on the surface over the carbon that causes it to show increasing RL vs freq.
This occurs in water loads used for long periods with tap water.? Calcium or magnesium or something in the water binds to the surface of the resistor and affects the performance vs freq.? I knew first hand this happening with a person using well water to cool a Bird load.
Not sure if old oil can contaminate a load though.?
The remedy is to clean the resistor rod using alcohol followed by baking soda in hot water.??
?If that fails then a new resistor might be available from Altronic Research in Yellville AR. They make resistors.
GL? Reid? W6MTF
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I gave up the oil loads years ago. Also supposed to use a special silicone oil which is not cheap.
I use air cooled loads, this one came out of the att ship to shore site in ocean gate New Jersey.
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On 2024-06-13 11:15, Brandon DX via groups.io wrote: Scott, I wonder if the resistor may have been replaced with one from a
contaminated load or a water load,
not knowing the history on it makes it a Sherlock Holmes case.
Measuring near 50 Ohms dc does show it has a good resistive element
though.
There are two types of elements used for load resistors like this, one
is a glass rod with the film deposited on it, the second is made of
bulk carbon.
I've seen the first type have a contaminated film on the surface over
the carbon that causes it to show increasing RL vs freq.
This occurs in water loads used for long periods with tap water.
Calcium or magnesium or something in the water binds to the surface of
the resistor and affects the performance vs freq. I knew first hand
this happening with a person using well water to cool a Bird load.
Not sure if old oil can contaminate a load though.
The remedy is to clean the resistor rod using alcohol followed by
baking soda in hot water.
If that fails then a new resistor might be available from Altronic
Research in Yellville AR. They make resistors.
GL Reid W6MTF
Links:
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[1] /g/ham-amplifiers/message/40432
[2] /mt/106621215/8135091
[3] /g/ham-amplifiers/post
[4] /g/ham-amplifiers/editsub/8135091
[5] /g/ham-amplifiers/leave/12941173/8135091/773995006/xyzzy
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In? lieu of a DL, what else that works is.....? 160m at high noon......and 10m at midnight.?
On 40m, just find some SW AM broadcast station, and tune all you want.??
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Maybe you can make a short jumper with some L or C (which ever's needed) to tune out the reactance at those UHF freqs? Bob W4JFA?
In? lieu of a DL, what else that works is.....? 160m at high noon......and 10m at midnight.?
On 40m, just find some SW AM broadcast station, and tune all you want.??
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I've been futzing with the Termaline.
Inside there is about a 14" long copper 'shell' that is the 'exponentially tapered line section'.? Inside the shell (which is the coaxial shield) is a 3/4" copper 'center conductor' that clamps to a plain ol' 6"x1" 50 ohm Carborundum tubular resistor (Type SP--rated for use in oil).
I have cleaned all the conducting junctions and substituted the resistor with another, and have checked multiple Bird QC connectors.? Sweeping the unit (outside of the oil bath) shows little change (VSWR ~ 2.7:1 at 435 MHz).
I'm thinking that the only thing left to go wrong is the oil itself.? The oil has some dielectric constant on the order of 2.5-3.0 (so I shouldn't expect to see 1:1) but I wonder (1) does Bird use some specific silicone oil that is controlled for dielectric constant?? and (2) would overheating the oil be a sufficient cause to make the input sweep so poorly when it's all put back together?
The Bird silicone oil is quite expensive and it would be good to have some comfort level for my diagnosis before possibly throwing good money after bad.
TIA,
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Hold on a sec Scott. If the resistor measures 2.7:1 out of oil it isn't going to improve when in oil. The mention of a copper center conductor makes me wonder if that was added or does it look original? I believe the correct geometry of the resistor is that it connects to the feedpoint with a short section of copper (silver plated) at the wide end of the outer ground plane tapering down to the diameter of the resistor element. If a resistor was added and is shorter than the original one then someone may have used a copper rod to extend it to make connection.
Its been a long time since I had my Bird load out and working on it. I bought the guts of a 1200W load from Don Payne in TN, it has a tapered section with a long (12 inch or more) resistive element, with holes in the tapered ground to allow oil to circulate.
I worked at the Rad Lab in Berkeley and was able to scrounge a nice long piece of rigid coax line with a flanged end for the load to mount on, it was capped off at the other end. They even furnished the oil which was out of a 50 gallon drum, can you imagine how much dielectric oil a cyclotron operation uses?? To be honest I haven't swept the load but at one time when I used it at 144MHz it was flat 1:1 so I would expect it to be J-zero out to 500 MHz.?
I believe the geometry of your resistor to the tapered ground plane may have been altered by someone, that would affect the VSWR vs. freq if the resistor is non-inductive carbon.??
Reid? ?W6MTF
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Hmm... I've attached some pix.? The one thing that doesn't fit is that the silver fitting on the wide end/front panel fits that 3/4" copper pipe perfectly; it will not fit any known (to me) dimension of Carborundum resistor.? Of course Bird could have them custom-made, which would explain the outrageous pricing on replacement parts. The second picture tries to show the insides.? The Carborundum resistor is more to the back end; you can see there is copper innards as you move to the wide end.? The resistor and the pipe are joined by a thin copper clamp about 1-1/2" long.? The last picture is the view from the wide end (the pipe is off-center because it has no support). I wish someone else who has the same load could take a pic of the resistor assembly for comparison.? My load appears to be an older version and doesn't quite fit the current documentation on the Bird website. One last item, I did check the silicone oil and the color does seem off...it's a lemon-yellow as opposed to clear or "slightly yellow" as Bird describes it.    
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I have never seen a price list for the spare load resistors for Bird Loads. I presume that the prices are horrendous.
When I inquired about overseas shipping of the Bird Load Silicone oil, it was almost more cost effective to buy a new load.
Long term as suggested Water or Air cooling is the way forward.
When I was looking for EMC amplifier loads and replacement Water cooled resistors this company was the most accommodating, communicated and quickly quoted prices. I dont know if they are still? around.
This company also sell proper high voltage surge resistors? for power supplies used in many broadcast transmitters.
When I checked their dimensions and part numbers they appeared very similar to the Bird and Altronic part numbers. Their physical sizes also matched the load resistor in many loads.?
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I guess I should consider myself fortunate. I got a gallon of silicon oil from work. It is use to keep the HV electrodes cool that make ozone for our DI water system/PW500. I put it in my old Heathkit Cantenna. One thing I notice is that I should have created a reservoir and installed a circulation pump. It makes a hot spot about in the middle of the can. Circulating it I probably could have made it capable of 2KW rather easily. ? Mod-U-Lator, Mike(y)/W3SLK ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of tardivat via groups.io
Sent: Wednesday, July 3, 2024 10:52 PM
To: [email protected]
Subject: Re: [ham-amplifiers] Bird Termaline load repair ? I have never seen a price list for the spare load resistors for Bird Loads. I presume that the prices are horrendous.
When I inquired about overseas shipping of the Bird Load Silicone oil, it was almost more cost effective to buy a new load.
Long term as suggested Water or Air cooling is the way forward.
When I was looking for EMC amplifier loads and replacement Water cooled resistors this company was the most accommodating, communicated and quickly quoted prices. I dont know if they are still? around.
This company also sell proper high voltage surge resistors? for power supplies used in many broadcast transmitters.
When I checked their dimensions and part numbers they appeared very similar to the Bird and Altronic part numbers. Their physical sizes also matched the load resistor in many loads.?
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Why focus on the ROS which hides an important parameter which is the reactif. Measure and show us the S11 with a nanaoVNA from 0 to 1 GHz. The variation on the Smith will tell you more than the SWR measurement. 73
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What is the swr at lower freqs..... like below 435 mhz ??? ? It needs to be swept from 1- 435 mhz.? ?It needs to be put on the VNA, like Francois noted.?
For all we know, it might be fine up to 150-200 mhz.....then above that, goes to hell......and fast.?
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If all else fails,? you could just feed power into a 435 mhz ant, like a 1/4 GP / dipole / small yagi .....in the garage or basement etc.?
How much power does the DL have to handle? @ 435 mhz ???? ?If the existing DL is good up to 54 mhz, or 144 mhz...... and only low power is used on 435 mhz.... perhaps a separate, lower powered? DL could be used for 220/440 mhz bands.?
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In some counties Baby Oil is a mineral oil and suitable for electrical
cooling. It is also possible to drain the oil from a discarded electric
radiator which in my experience is similar but less viscous. I am sure
none of these would be as good as the Bird oil but maybe OK for amateur
use.
Mike
VK2AMF.
At 04:51 AM 4/07/2024, you wrote:
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I have never seen a price list
for the spare load resistors for Bird Loads. I presume that the prices
are horrendous.
When I inquired about overseas shipping of the Bird Load Silicone oil, it
was almost more cost effective to buy a new load.
Long term as suggested Water or Air cooling is the way forward.
When I was looking for EMC amplifier loads and replacement Water cooled
resistors this company was the most accommodating, communicated and
quickly quoted prices. I dont know if they are still?
around.
This company also sell proper high voltage surge resistors? for
power supplies used in many broadcast transmitters.
When I checked their dimensions and part numbers they appeared very
similar to the Bird and Altronic part numbers. Their physical sizes also
matched the load resistor in many loads.?
Mike Fleetwood
Canberra Australia and Sidcup UK.
Worldwide email address
is:?????
mfleetwood@...
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Typ, the local power company will give u a few gallons? of xfmr oil.? ?I used that in the heath dl....and also my HB? 8 gallon DL.? ?But neither are used above 10m.?
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Mineral oil will work too, but has to be de-rated vs the real deal xfmr oil.? (note the 2 x graphs on the heath cantenna).? ?Bird used some esoteric silicone oil in their loads.?
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OP, how much PO are u gonna put into a DL on 435 mhz ???
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So really the point is that I want the load to operate according to specifications:? VSWR 1.1:1 0-1 GHz; 1.25:1 1-2 GHz.? This one can't make spec above 30 MHz. Here is another picture of the innards.? At top is the tapered outer conductor.? Middle is the RF input (Bird QC connectorm, not visible to the right) and the inner conductor/resistor.? The copper piece interfacing directly with the resistor end is a screw-tightened clamp which is obviously hand-made.? The id of the fingerstock bit is 0.875", a perfect fit for 3/4" copper pipe, but not for any known (to me) non-inductive resistor. The tapered section looks similar to others I've seen online. I now have a 12" long 50 ohm non-inductive resistor, which will use up the entire length of the tapered section.? I can make more Cu plumbing to adapt the fingerstock to the resistor, but it just seems really odd to me that Bird would do it this way.? Wouldn't it have made more sense for the fingerstock to fit 1.0" id? 
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Brandon DX
Bob