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Author Topic: SB-220 Integrated HV fuse & Glitch Resistor Images (2)  (Read 24992 times)
WA7PRC
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« Reply #15 on: January 03, 2018, 06:34:07 PM »

Effective high voltage fuses are costly and most manufactures are cheap.  A cheap fuse that allows a plasma arc across the blown fuse element until the  HV caps are almost depleted is useless.  Thermal circuit breakers are slow devices.
A MWO fuse is inexpensive but, not necessary.

There were better grade amps that used dual section plate caps that provided a reasonable tuning rate on the higher ranges; the vernier is again a cheaper option for easier tuning on ten meters. Some fools would argue power steering isn't needed because they can drive just fine without it.  Whatever. Some hams just troll for the sake of trolling.  Does anyone think Martin Jue would keep using vernier drives on his amps if hams didn't want that feature???
Maybe Martin sells them that way 'cuz some people want them that way. The rest of us can tune an amplifier either with or without vernier drives.

I love the ignore buttons.
I love CHOOSING to ignore (or not). Though, I sometimes wish the Ignore "feature" worked in reverse, causing certain posters to not see my posts.
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N8CBX
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« Reply #16 on: January 04, 2018, 09:02:12 AM »

If one is serious about parasitic suppression, use the original parasitic traps.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
KD9IQO
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« Reply #17 on: January 04, 2018, 09:28:07 AM »

Can you provide research documents to support that assertion?
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W1BR
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Posts: 4188




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« Reply #18 on: January 04, 2018, 09:52:24 AM »

Assuming the original chokes were chosen correctly,  then there is some wisdom to staying with those values for that amp. Parasitic chokes aren't universal.  they can be too lossy, or ineffective.  The question I'd ask is how those chokes were tested and evaluated to ensure how well they will act in that amp.  Below is how I would approach repair or replacement.

https://www.w8ji.com/testing_for_stability.htm
https://www.w8ji.com/vhf_stability.htm

73


Pete
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KD9IQO
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« Reply #19 on: January 04, 2018, 10:25:31 AM »

I appreciate the way W8JI documents his assertions.  I read, catalog, and sometimes re-create the experiments of W8JI and others.  He has provided so much valuable (free) research that sometimes I feel guilty about the free lunch.  Maybe I should start a go-fund-me page for W8JI.

However, my article is NOT about parasitic oscillations......it's about OCP for the tubes.  There are many reasons an over-current condition can occur.
« Last Edit: January 04, 2018, 10:29:26 AM by KD9IQO » Logged
AF6LJ
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Posts: 582




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« Reply #20 on: January 04, 2018, 10:39:00 AM »

Tom's chokes are overly complicated and it is unnecessary in the case of the SB-220.
The amplifier is stable when properly loaded. The only time a properly built SB-220 will arc is;
1. When the amplifier is not properly loaded. The amplifier should not be tuned to maximum output and left under that lightly loaded state, add a little loading (5% reduction in output power) and the amplifier won't have the tun cap arc over.
2. Overdriving the amplifier; the SB-220 is designed to be driven with 100W, and not much more.
3. Run the amplifier into its rated VSWR.

KISS
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Take Care
Sue,
AF6LJ

Don't Kalifornicate My Life
W1BR
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Posts: 4188




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« Reply #21 on: January 04, 2018, 10:58:28 AM »

And when the antenna relay contacts are misaligned and allow RF on the cathodes before the tank sees a load.
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W1QJ
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« Reply #22 on: January 04, 2018, 11:42:19 AM »

And when the antenna relay contacts are misaligned and allow RF on the cathodes before the tank sees a load.
   

The #1 reason and this is why I advocate timing your relay.
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KD9IQO
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Posts: 10




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« Reply #23 on: January 04, 2018, 11:44:40 AM »

Both my SB-200 and SB-220 contain the well-designed W7RY circuit boards.
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W1BR
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Posts: 4188




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« Reply #24 on: January 04, 2018, 11:58:59 AM »

Both my SB-200 and SB-220 contain the well-designed W7RY circuit boards.

I bought the raw parts from MaxGain and roughly followed Measures QSK design--much cheaper, but the RY boards are dressy looking.  I added 160 meter and full WARC coverage (used the TU6b WD7S input board) to my SB-220 along with automatic bias switching--and a vernier reduction drive and new black panel to give my stalker in 7 land some things to rail over.  Most of us modify  rigs to meet our expectations and needs.  Regardless of the never ending debate over Harbach, his new power supply and metering boards are well worth the cost and effort.  I won't broach the nichrome voodo--LOL!   Cheers! Pete
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N8CBX
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« Reply #25 on: January 04, 2018, 12:45:45 PM »

Can you provide research documents to support that assertion?
Pages 17.22 -17.23 in the ARRL Handbook for Radio Communications, 90th edition.
The suppressor in the SB-200 & 220 is what is called the "Classic" suppressor.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
KD9IQO
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« Reply #26 on: January 04, 2018, 01:42:32 PM »

Sad  Cry
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K8BYP
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Posts: 256




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« Reply #27 on: January 04, 2018, 03:16:25 PM »

OH and PS

Something struck me as odd about this last nite, took a while to catch the error...

The MW oven fuse IS NOT A HV FUSE IN A MW OVEN. (or at least not a HV fuse application)

It operates on exactly the same AC line as any other 120/250VAC fuse. The microwave oven fuses are in the 120VAC line, NOT the HV line.


Sorry, its been a few years since Ive worked on lots of MWs and other electronics, took a while to catch the gross mistake.

Digi Key lists ceramic fuses max of 1Kv. You're using it in a 2.5 KV circuit.
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W1BR
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« Reply #28 on: January 04, 2018, 03:42:13 PM »

Can't anyone Google properly?HuhHuhHuhHuhHuhHuhHuhHuhHuh?

  Huh Huh Huh

Microwave Oven High Voltage Fuse 800mA 0.8A  5kV
 
High quality replacement type high voltage fuse for modern microwave ovens. This high voltage fuse is wired in series with the high voltage feed from the high voltage transformer to the magnetron.

 
The fuse will fail if there is a fault in the high voltage circuit. Such a fault could be a short circuit magnetron or a short circuit high voltage rectifier. In our experience however this fuse commonly fails for no apparent reason. The fuse just gets stressed everytime the magnetron starts which eventually leads to the demise of the fuse.
 
If you have a microwave with this type of fuse then the symptom you will get if it has failed is no cooking action. The microwave will appear to start and countdown the time but there will be no heating action.
 
The fuse is easy to check visibly by unscrewing the fuse housing apart as shown in the photograph. You can then visually examine the wire in the fuse to see if it has broken. For the more technically minded a continuity check with an ohm meter will also check the fuse. A short circuit reading should be obtained if the fuse is intact.
 
This is the technical specification of the fuse:
 
Current rating 800mA, 0.8A
Voltage rating 5kV
Overall length of fuse including the cables 330mm
Fuse housing length 95mm
Fuse housing diameter 14mm
Connection, 2 x 6.3mm insulated spade terminals
« Last Edit: January 04, 2018, 03:46:01 PM by K1ZJH » Logged
W1BR
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Posts: 4188




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« Reply #29 on: January 06, 2018, 08:09:26 PM »

While doing some research I found this recent thread in the amps forum.

I didn't see any  concerns  about using both a  HV fuse and a current limiting fuse in tandem.
 
Scroll down for that thread:

http://lists.contesting.com/pipermail/amps/2017-November/thread.html
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