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Author Topic: SB-220 Integrated HV fuse & Glitch Resistor Images (2)  (Read 24996 times)
KD9IQO
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« on: January 02, 2018, 12:48:23 PM »

Offered for your consideration:  My technique for neatly integrating an insurance policy into your SB-220.

http://cubeupload.com/im/KD9IQO/KD9IQO3A.jpg

http://cubeupload.com/im/KD9IQO/DSC5437KD9IQO.jpg
 
de......KD9IQO
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WB4SPT
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« Reply #1 on: January 02, 2018, 01:06:06 PM »

Looks nice.   Lots of non-Heath stuff in there.   What's inside that 5kV fuseholder?
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KD9IQO
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« Reply #2 on: January 02, 2018, 01:12:51 PM »

A rather long 0.9 Ampere HV (microwave oven) glass fuse.
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W1BR
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« Reply #3 on: January 02, 2018, 02:21:47 PM »

Good idea on the fuse, where do you find them?
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KD9IQO
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« Reply #4 on: January 02, 2018, 02:28:51 PM »

Microwave oven fuses (with the explosion-resistant housing) can be purchased on eBay.  The resistor is a wire-wound, vitreous-enameled 50Ω at 50 Watt unit.

de...KD9IQO
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AF6LJ
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« Reply #5 on: January 02, 2018, 08:03:52 PM »

The glitch resistor is located in a reasonable place.
The only drawback to locating it there is it gets in the way when making power supply repairs.
Not that big of a deal though.

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Sue,
AF6LJ

Don't Kalifornicate My Life
K8BYP
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« Reply #6 on: January 03, 2018, 04:16:52 PM »

1. That fuseholder boldly claims "5Kv" but Ill bet that wire ISNT able to handle that. That appears to be fairly thin insulation with a cotton cover (the cotton cover offers no voltage isolation to speak of.. its full of holes- I found several wires insulated with only cotton braid arcing to the chassis in my TR-3).

Look at the insulated wire diameter in a typical MW oven HV circuit which is about 2200VDC. I think its about 3/16th of an inch. That fuseholder wire looks about the size of the Alpha wire rated at 1Kv.

2. Instead of messing with the plate lead, put the fuse in the cathode side, low voltage. Opening either side of the B supply will turn the juice off!

3. Recent memory is from either the 4-400 or 3-500 technical info, some warning about 'not running the tube without plate voltage' and something about grid or screen current skyrocketing if plate voltage is lost. If the plate supply is lost, that's the same as "no plate voltage which would happen if the fuse pops. Since its grounded grid service and only one PS, I dont see how that could happen.

3 Shame (x14) on whomever used, as HK originally did, low voltage rectifiers without equalization. That's begging for a cascade failure. I know the original design used a series string without any protection..BUT...just because Heathkit did it doesnt make it right. (the 14x factor is for the 14 diodes that may go up in smoke on a big transient)

There are real HV rectifiers out there, no reason to use mickey- mouse LV rectifier strings these days. Yes, they are $15 each, but they are real HV units and only need two and no eq components

3. Nice clean looking amp inside! Sadly, 1 Kw on 40m these days will get you half way across the country with these horrible condx. HI
« Last Edit: January 03, 2018, 04:19:42 PM by K8BYP » Logged
W1BR
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« Reply #7 on: January 03, 2018, 04:30:11 PM »

Modern avalanche mode diodes do not need equalizing resistors--the need for those resistors went out with high button shoes.  They are counter productive and increase the number of parts that can fail.

I have some 5-kV  rated wire that is surprisingly slim.  You can't judge a book by its cover.
 
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WA7PRC
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« Reply #8 on: January 03, 2018, 04:58:01 PM »

1. That fuseholder boldly claims "5Kv" but Ill bet that wire ISNT able to handle that. That appears to be fairly thin insulation with a cotton cover (the cotton cover offers no voltage isolation to speak of.. its full of holes- I found several wires insulated with only cotton braid arcing to the chassis in my TR-3).

Look at the insulated wire diameter in a typical MW oven HV circuit which is about 2200VDC. I think its about 3/16th of an inch. That fuseholder wire looks about the size of the Alpha wire rated at 1Kv.
With a glitch resistor, a fuse isn't needed (the mains breakers will blow). That's how the glitch resistor is intended to function.

2. Instead of messing with the plate lead, put the fuse in the cathode side, low voltage. Opening either side of the B supply will turn the juice off!
It's a VERY bad idea to fuse the low side. If that was a good idea, the Neutral would be fused instead of the Line.

3 Shame (x14) on whomever used, as HK originally did, low voltage rectifiers without equalization. That's begging for a cascade failure. I know the original design used a series string without any protection..BUT...just because Heathkit did it doesnt make it right. (the 14x factor is for the 14 diodes that may go up in smoke on a big transient)

There are real HV rectifiers out there, no reason to use mickey- mouse LV rectifier strings these days. Yes, they are $15 each, but they are real HV units and only need two and no eq components
That used to be the case, several decades ago. Today, rectifiers are MUCH better... and much less costly. Jameco has 1N5408s (3A/1KV) for $0.10 each in 10+ lots. Others have 'em for under two bits/each. No "equalizing" is needed.

Sadly, 1 Kw on 40m these days will get you half way across the country with these horrible condx. HI
I've been doing it w/ only 100W, my SB-220 is mostly idle.
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KD9IQO
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« Reply #9 on: January 03, 2018, 05:18:40 PM »

No fuse or circuit breaker is quick enough to protect the tubes from an arc-over.  The glitch resistor is there to limit the arc-over current to 70 Amps while the fuse element vaporizes, deposits on the glass envelope, then cools and finally stops arc current.  The amplifier circuit breakers are not there to protect the amplifier.  The two circuit breakers are there to protect your home's wiring.  They are both too slow to serve as protection for the amplifier. 

Professor Roy C Long, Chair
School of Technology
Ivy Tech Community College
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W1BR
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« Reply #10 on: January 03, 2018, 05:33:05 PM »

Circuit breaker won't do squat for stored energy.  Glitch resistors are indeed cheap insurance.
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WA7PRC
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« Reply #11 on: January 03, 2018, 05:36:09 PM »

Quote
No fuse or circuit breaker is quick enough to protect the tubes from an arc-over.  The glitch resistor is there to limit the arc-over current to 70 Amps while the fuse element vaporizes, deposits on the glass envelope, then cools and finally stops arc current.  The amplifier circuit breakers are not there to protect the amplifier.  The two circuit breakers are there to protect your home's wiring.  They are both too slow to serve as protection for the amplifier. 

Professor Roy C Long, Chair
School of Technology
Ivy Tech Community College
Wow. Just... WOW.  Roll Eyes

Over the past few decades, the subject has been hashed-out ad nauseam on the various ham amplifier reflectors. Either the glitch resistor OR the HV fuse is appropriate. Both are not needed. If both were needed, ham amplifier manufacturers would have included both.

This ain't rocket science (your title doesn't impress).
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KD9IQO
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« Reply #12 on: January 03, 2018, 05:40:29 PM »

BOTH are needed.
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AF6LJ
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Posts: 582




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« Reply #13 on: January 03, 2018, 05:59:18 PM »

Quote
No fuse or circuit breaker is quick enough to protect the tubes from an arc-over.  The glitch resistor is there to limit the arc-over current to 70 Amps while the fuse element vaporizes, deposits on the glass envelope, then cools and finally stops arc current.  The amplifier circuit breakers are not there to protect the amplifier.  The two circuit breakers are there to protect your home's wiring.  They are both too slow to serve as protection for the amplifier. 

Professor Roy C Long, Chair
School of Technology
Ivy Tech Community College
Wow. Just... WOW.  Roll Eyes

Over the past few decades, the subject has been hashed-out ad nauseam on the various ham amplifier reflectors. Either the glitch resistor OR the HV fuse is appropriate. Both are not needed. If both were needed, ham amplifier manufacturers would have included both.

This ain't rocket science (your title doesn't impress).
I miss my Like Button...
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Sue,
AF6LJ

Don't Kalifornicate My Life
W1BR
Member

Posts: 4188




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« Reply #14 on: January 03, 2018, 06:22:15 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.

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???  I love the ignore buttons.
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