It would take the op all of 30 secs to parallel the 2 x 100 ohm resistors and see if they are inductive.? ?Heck only 1 is required for this test.??
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Thanks for all the replies. I don't need a dummy load, I just have this stuff laying around. I'll probably just try for the heck of it. Again, thanks for the replies.
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Hi ¨C ? I would say giver it a try. Put it together and then use a network or antenna analyzer and check the DL for return loss. 73 ¨C Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 ?
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From: [email protected] < [email protected]> On Behalf Of N0EE via groups.io Sent: Thursday, September 28, 2023 10:14 PM To: [email protected]Subject: [ham-amplifiers] Dummy Load Resistor ? I'm wondering if a Planar resistor can be used for an RF dummy load. I have a couple 1KW 100 ohm Planar resistors and an 18# heat sink, I can't find my answer anywhere. Any information will be greatly appreciated.
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Scott,
I may be reading too much into this, but when people post to a group named "ham-amplifiers" and mention "a couple 1KW ... resistors" I can only assume that they plan to homebrew an HF dummy load.
They'd be much better off to buy a surplus dummy load in the 5 kW range that's good to at least 6 meters, preferably higher.? There may be some FM broadcast surplus kicking around ...? I know a guy who knows some guys.? Whatever.
73 Jim N6OTQ
You can always take two of the 50 ohm resistors in series,
paralleled with another two 50 ohm resistors in series.
Should give you 400 watts of dissipation.
I'm using 2 paralleled strings of 4-100 ohm resistors
to get 200 ohms capable of dropping the 8 watts
to slow a fan down cooling my stereo. (120VAC)
They are 1 watt resistors I had in my junque box.
On 2023-09-28 22:23, Jim Strohm wrote:
> ebay has some 50 ohm non-inductive resistors?but they're not good for
> much more than 100 watts and most are 50 ohms.? For higher power
> values, you'll need to search the surplus channels.? Just how big a
> dummy load do you need, anyway?
>
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Mite want to check the SWR of it or a scan with a VNA or some such to see how it looks.
A
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On 9/28/2023 9:43 PM, Scott, KB3JQQ via groups.io wrote: You can always take two of the 50 ohm resistors in series,
paralleled with another two 50 ohm resistors in series.
Should give you 400 watts of dissipation.
I'm using 2 paralleled strings of 4-100 ohm resistors
to get 200 ohms capable of dropping the 8 watts
to slow a fan down cooling my stereo. (120VAC)
They are 1 watt resistors I had in my junque box.
On 2023-09-28 22:23, Jim Strohm wrote:
ebay has some 50 ohm non-inductive resistors?but they're not good for much more than 100 watts and most are 50 ohms.? For higher power values, you'll need to search the surplus channels.? Just how big a dummy load do you need, anyway?
--
"Where the Old Soo crossed the New Soo"
Duplainville, Wisconsin
Web page: Http:/www.dupyrail.com
Youtube Channel:
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Reminds me, I built a dummy load with twenty half watt
1000 ohm resistors in parallel between two coax braids
dunked in a gallon of ND30 motor oil in a one gallon pain can.
I haven't killed it yet using up to one minute tests with 100+ watts.
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On 2023-09-28 22:43, Scott, KB3JQQ via groups.io wrote: You can always take two of the 50 ohm resistors in series,
paralleled with another two 50 ohm resistors in series.
Should give you 400 watts of dissipation.
|
You can always take two of the 50 ohm resistors in series,
paralleled with another two 50 ohm resistors in series.
Should give you 400 watts of dissipation.
I'm using 2 paralleled strings of 4-100 ohm resistors
to get 200 ohms capable of dropping the 8 watts
to slow a fan down cooling my stereo. (120VAC)
They are 1 watt resistors I had in my junque box.
toggle quoted message
Show quoted text
On 2023-09-28 22:23, Jim Strohm wrote: ebay has some 50 ohm non-inductive resistors?but they're not good for much more than 100 watts and most are 50 ohms.? For higher power values, you'll need to search the surplus channels.? Just how big a dummy load do you need, anyway?
|
John,
Does the datasheet for that "planar resistor" say it's non-inductive?? If not, then it probably won't work as a dummy load, except at audio.
ebay has some 50 ohm non-inductive resistors?but they're not good for much more than 100 watts and most are 50 ohms.? For higher power values, you'll need to search the surplus channels.? Just how big a dummy load do you need, anyway?
73 Jim N6OTQ
I'm wondering if a Planar resistor can be used for an RF dummy load. I have a couple 1KW 100 ohm Planar resistors and an 18# heat sink, I can't find my answer anywhere. Any information will be greatly appreciated.
|
I'm wondering if a Planar resistor can be used for an RF dummy load. I have a couple 1KW 100 ohm Planar resistors and an 18# heat sink, I can't find my answer anywhere. Any information will be greatly appreciated.
|
Re: Plate modulated GG triodes
Jim, that sound about right.? Years ago I ran a Ranger and a Thunderbolt amp.? This combo is very inefficient.? ?In AM mode they ran the pair of 4-400 with 350 MA if idle current. Then, they had your drive the amp up to 10 to 15 ma of grid current. You ended
up with nuclear hot tubes, 300watts and no peaks.? No matter how you loaded it, It would never show any peak power.
One day I decided to switch the T bolt in to Class C.? It has that mode for CW.? Then, I drove the ranger into it.? It took twice the drive but the ranger could do that easily with the padder removed.??
I ended up with a cool running amp, 1200 pep from a 300 watt carrier.? I checked it both ways on my Spec AN and found 1 db of difference. ALL of the heat was gone.??
I am unsure what would happen if you added the choke.? It might be worth a try.
We tried many different methods.? Including applying audio to the grid via a transformer.?
The way Gates handled this was to have a separate winding on the mod trans. This winding modulated the Driver tube.? This way the drive power is modulated.
What I want to try and will soon, is to modulate the drive on a plate modulated rig.?
In the case of my friends rig, There is 60 watts not modulated as drive for the 500 ish watt of carrier unless you come up with a way to modulate it, That 60 watts just sits there on the scope
C
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Just curious, the feed through power of a G-G Amp might be ~ 2 to 5% of the power output when the tube has a high Mu. For a low Mu tube, that could be upwards of 20%. The self modulated control grid adds a new to me concept that I never have seen before.
I presume the Plate Modulated GG triode is run class C?
If the feed through power is low, the limitation to downward modulation will be minimal. A high Mu tube needs a bit of a kick in the pants to get to plate current saturation, where the peak grid-cathode swing is way positive, and drawing significant grid current.
A low Mu tube might reach the same saturation plate current at zero bias where there is no grid current, but a much larger swing in voltage grid to cathode.
I run a Gonset GSB-201 with 4 Russian 811A's (high Mu) for AM. On AM I use 12v bias, which at 1500v B+, the tubes idle at the edge of cutoff. For SSB I use -4.5v with an idle current at about 60ma.
On AM, old texts from the 1930's call this class BC amplification. What is the result?
* very clean (AM)
* gain drops from 10 db to about 7 db (takes more drive)
* resting carrier efficiency changes from around 30% to about 38%
* I can achieve 800w PEP from a 150-175 watt carrier that has a drive that has asymmetrical modulation. With normal mode (-4.5v bias), the drive is reduced (more gain), efficiency drops, and max PEP output drops to around 600 watts PEP
* With Class BC, the output modulation percentage is about 5% higher than the modulation percentage of the driver stage.
So, If I biased my Amp class C (maybe 24v bias), added a grid choke (20H), and plate modulated the 811A plates, then what would happen?
Jim
Wd5JKO
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Re: Plate modulated GG triodes
Just curious, the feed through power of a G-G Amp might be ~ 2 to 5% of the power output when the tube has a high Mu. For a low Mu tube, that could be upwards of 20%. The self modulated control grid adds a new to me concept that I never have seen before. I presume the Plate Modulated GG triode is run class C?
If the feed through power is low, the limitation to downward modulation will be minimal. A high Mu tube needs a bit of a kick in the pants to get to plate current saturation, where the peak grid-cathode swing is way positive, and drawing significant grid current. A low Mu tube might reach the same saturation plate current at zero bias where there is no grid current, but a much larger swing in voltage grid to cathode.
I run a Gonset GSB-201 with 4 Russian 811A's (high Mu) for AM. On AM I use 12v bias, which at 1500v B+, the tubes idle at the edge of cutoff. For SSB I use -4.5v with an idle current at about 60ma.
On AM, old texts from the 1930's call this class BC amplification. What is the result?
* very clean (AM)
* gain drops from 10 db to about 7 db (takes more drive)
* resting carrier efficiency changes from around 30% to about 38%
* I can achieve 800w PEP from a 150-175 watt carrier that has a drive that has asymmetrical modulation. With normal mode (-4.5v bias), the drive is reduced (more gain), efficiency drops, and max PEP output drops to around 600 watts PEP
* With Class BC, the output modulation percentage is about 5% higher than the modulation percentage of the driver stage.
So, If I biased my Amp class C (maybe 24v bias), added a grid choke (20H), and plate modulated the 811A plates, then what would happen?
Jim
Wd5JKO
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Re: 3CX-10,000A7 for sale...... $2500.00
The tube hi-pot tests 30 kv (anode to grid)...and? 5 kv (grid to cathode).? This is normal for a 3x10.?
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Re: Operating RTTY FSK and Alpha 86
I went to local "Lowe's" hardware (may not be same in VE) and bought foam filter material ($4) and cut to fit.
Frost King 15-in W x 24-in L x 0.1875-in Washable Cut To Fit Air Filter
if the link doesn't work, go to Lowes site ( HomeDepot does similar, etc.)?? and search for foam filter. $4 and picked up same day.? Cut and installed on Acom 2000A - great option.
73 W5AJ Robert
On Fri, Sep 8, 2023 at 9:25?AM James Wolf < kr9u@...> wrote: Jim, ? Can you point us to a good filter material to use?? Maybe a link? ? Jim ¨C KR9U ? ? This is exactly why you install or retrofit a filter on the air intake.?
On a side note, a shop vac on the bottom of the tube will get most of the crud + dust out...from the bottom.? ? Then try compressed air from the top. Then stick it in the dishwasher....that works superb.? ? Go to 3M's? home page.? ?They make filters as small as 7" x 7".? ?They also have washable, and cutable filters, that can be cut to fit a specific size.
Don't get ur fingers on the ceramic.? Any skin oil / fingerprints etc, will result in reduced hi-pot test results.
Jim? VE7RF
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3CX-10,000A7 for sale...... $2500.00
Scott, KB1SEL (amprepairguy.com) has a recently rebuilt (by Econco) Svetlana 3CX-10,000A7 for sale.? ZERO hours on the rebuilt tube....and also a full warranty.
Contact Scott Mitchell at KB1SEL@... or phone him at (203) 892-4119
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This is why I bought that 0-15 kvdc? hi-pot tester from W8JI.? Ur dead in the water without it.?
Hi-pot from anode to grid ( with grid temp bonded to cathode)
Then hi-pot from grid to cathode ( with anode temp bonded to grid).?
If the grid is shorted to the cathode? ( tube on bench, with a dvm between grid and cathode)? you have a 50% chance of clearing it.? Temp apply ( quick blip) 12 vdc from a car battery between grid and cathode.?
It will either:
(A)? blow it open
(B)? weld it permanently closed.?
?
Lou, what is typ hi-pot test results on a GOOD? 572B? ( anode to grid...... and grid to cathode)? ???
Jim? ?VE7RF
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Thanks Alek. Another friend mentioned a tube tester. I have one but it's put away and hasn't been powered up for about 7 years. I'll have to see if it'll test them. 73 Bob W4JFA?
It is very simple to check. Use a 1kV Megger or even a 500V one
and measure between grid and filament and I bet it will show big
conduction. You will also see the blue glow deep inside and the
occasional flashover, if you're lucky. The Megger is a high
impedance output, so you are not going to get any catastrophic
events by doing this.
73, Alek VK6APK
On 8/09/2023 11:15 pm, Bob wrote:
That's prolly the answer. I put my friends amp
back together so I cannot test it now plus it obviously puts
stress on everything so I'll mark it bad and test it at a later
date.
Your theory makes sense.
Thanks.
Bob W4JFA?
On Fri, Sep 8, 2023, 11:07 AM
Chuck Neal < cdoneal@...>
wrote:
The
tube is likely gassy and will only conduct when HV is
applied.? It usually takes a few hundred volts for a
gassy tube to conduct so the low voltage from a test
meter will not reveal a gassy tube.
?
Hint:?
Watch the tube upon applying HV.? You might see a
quick bluish flash before the fuse goes.
?
-Chuck
K1KW
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B
?
Hi all,
I'll condense this, you'lll get
the idea.
A friend has an 811H with 3 year
old 572B's. One shorted?and causes the fuse to blow
immediately. Tube replaced and all is well.
Measuring with a DVOM shows no
shorts at all. I do know some tubes will short after
they get warm/hot but this one blows the fuse
immediately (no time to get hot) but does not
measure any short circuit.
I've now talked to two other hams
on the air that say the exact same thing happened to
them.
|
It is very simple to check. Use a 1kV Megger or even a 500V one
and measure between grid and filament and I bet it will show big
conduction. You will also see the blue glow deep inside and the
occasional flashover, if you're lucky. The Megger is a high
impedance output, so you are not going to get any catastrophic
events by doing this.
73, Alek VK6APK
On 8/09/2023 11:15 pm, Bob wrote:
toggle quoted message
Show quoted text
That's prolly the answer. I put my friends amp
back together so I cannot test it now plus it obviously puts
stress on everything so I'll mark it bad and test it at a later
date.
Your theory makes sense.
Thanks.
Bob W4JFA?
On Fri, Sep 8, 2023, 11:07 AM
Chuck Neal < cdoneal@...>
wrote:
The
tube is likely gassy and will only conduct when HV is
applied.? It usually takes a few hundred volts for a
gassy tube to conduct so the low voltage from a test
meter will not reveal a gassy tube.
?
Hint:?
Watch the tube upon applying HV.? You might see a
quick bluish flash before the fuse goes.
?
-Chuck
K1KW
?
From:
[email protected]
[mailto:[email protected]]
On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B
?
Hi all,
I'll condense this, you'lll get
the idea.
A friend has an 811H with 3 year
old 572B's. One shorted?and causes the fuse to blow
immediately. Tube replaced and all is well.
Measuring with a DVOM shows no
shorts at all. I do know some tubes will short after
they get warm/hot but this one blows the fuse
immediately (no time to get hot) but does not
measure any short circuit.
I've now talked to two other hams
on the air that say the exact same thing happened to
them.
|
Lou, No intention on using it again. It would be good to be able to diagnose for the future. Since it blew the fuse immediately it didn't appear to be a heat issue to me but the explanation above makes sense.
My friend went from 811 to 572 for longevity. That didn't work!
This is the amp that I got parts for from you a year ago or so if you remember.
Bob W4JFA?
On Fri, Sep 8, 2023, 11:49 AM Louis Parascondola via <Gudguyham= [email protected]> wrote:
9 times outta 10 you won¡¯t find a shorted tube ohming ?it with a meter.? If you catch a tube short with a meter it¡¯s because the grid is obliterated and debris is all over.? Once Chinese tubes short best to Chuck in the garbage.
On Friday, September 8, 2023, 11:18 AM, Jim Strohm <jim.strohm@...> wrote: Another piece of ham lore is -- if you run the heater for a day, the getter will get hot and absorb the gas.
That's worth a try, and won't set your backyard or basement on fire.
73 Jim N6OTQ
On Fri, Sep 8, 2023 at 10:07?AM Chuck Neal < cdoneal@...> wrote: The tube is likely gassy and will only conduct when HV is applied.? It usually takes a few hundred volts for a gassy tube to conduct so the low voltage from a test meter will not reveal a gassy tube. ? Hint:? Watch the tube upon applying HV.? You might see a quick bluish flash before the fuse goes. ? -Chuck K1KW ? From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B ? Hi all, I'll condense this, you'lll get the idea. A friend has an 811H with 3 year old 572B's. One shorted?and causes the fuse to blow immediately. Tube replaced and all is well. Measuring with a DVOM shows no shorts at all. I do know some tubes will short after they get warm/hot but this one blows the fuse immediately (no time to get hot) but does not measure any short circuit. I've now talked to two other hams on the air that say the exact same thing happened to them.
|
9 times outta 10 you won¡¯t find a shorted tube ohming ?it with a meter. ?If you catch a tube short with a meter it¡¯s because the grid is obliterated and debris is all over. ?Once Chinese tubes short best to Chuck in the garbage.
On Friday, September 8, 2023, 11:18 AM, Jim Strohm <jim.strohm@...> wrote: Another piece of ham lore is -- if you run the heater for a day, the getter will get hot and absorb the gas.
That's worth a try, and won't set your backyard or basement on fire.
73 Jim N6OTQ
On Fri, Sep 8, 2023 at 10:07?AM Chuck Neal < cdoneal@...> wrote: The tube is likely gassy and will only conduct when HV is applied.? It usually takes a few hundred volts for a gassy tube to conduct so the low voltage from a test meter will not reveal a gassy tube. ? Hint:? Watch the tube upon applying HV.? You might see a quick bluish flash before the fuse goes. ? -Chuck K1KW ? From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B ? Hi all, I'll condense this, you'lll get the idea. A friend has an 811H with 3 year old 572B's. One shorted?and causes the fuse to blow immediately. Tube replaced and all is well. Measuring with a DVOM shows no shorts at all. I do know some tubes will short after they get warm/hot but this one blows the fuse immediately (no time to get hot) but does not measure any short circuit. I've now talked to two other hams on the air that say the exact same thing happened to them.
|
If the tube is loose and rolling around, you can get / make / borrow a 6.3V supply and hook up the filament with clip leads.? You don't need a socket, and you especially don't need the amp that the tube came out of for burning in a suspected gassy tube.
You'll want a regulated supply and a reasonably accurate digital voltmeter to dial up 6.3V at 4A.? The tube specs usually?say?+/- 0.3V on the 6.3V -- I've found?that our modern electricity, which is higher than the old nominal?110VAC, can destroy tubes.? I lost a 117N7 tube this week by over-volting the filament.? Grrr. ? I hope I can find another one.? And I need to pay attention to line voltages a little more closely.
Maybe there'll be some good Constavolt supplies at the next swap fest. ?
73 Jim N6OTQ ???
That's prolly the answer. I put my friends amp back together so I cannot test it now plus it obviously puts stress on everything so I'll mark it bad and test it at a later date. Your theory makes sense. Thanks. Bob W4JFA?
On Fri, Sep 8, 2023, 11:07 AM Chuck Neal < cdoneal@...> wrote: The tube is likely gassy and will only conduct when HV is applied.? It usually takes a few hundred volts for a gassy tube to conduct so the low voltage from a test meter will not reveal a gassy tube. ? Hint:? Watch the tube upon applying HV.? You might see a quick bluish flash before the fuse goes. ? -Chuck K1KW ? From: [email protected] [mailto:[email protected]] On Behalf Of Bob
Sent: Friday, September 08, 2023 10:21 AM
To: Ham Amplifiers Ham Amplifiers
Subject: [ham-amplifiers] 572B ? Hi all, I'll condense this, you'lll get the idea. A friend has an 811H with 3 year old 572B's. One shorted?and causes the fuse to blow immediately. Tube replaced and all is well. Measuring with a DVOM shows no shorts at all. I do know some tubes will short after they get warm/hot but this one blows the fuse immediately (no time to get hot) but does not measure any short circuit. I've now talked to two other hams on the air that say the exact same thing happened to them.
|
Scott, KB3JQQ
Robert, W5AJ
Bob