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Author Topic: HV PSU to RF deck wiring safety qeustion  (Read 10515 times)
2E0ILY
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Posts: 143




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« on: November 11, 2012, 02:56:05 AM »

I have finished my HV supply for my conversion of a Henry RF generator to a linear amp. Please see attached schematic. I have proper HV connectors and cable to take the HV + from the PSU to the separate RF deck, but I am unsure if it's overkill also using HV connectors and HV wire to connect the -ve side, which, all being well. should only ever float just above ground. I added 3 safety diodes to conduct to ground in case of a flash over and a safety resistor to ground. In the original (single cabinet) Henry RF generator and PSU ordinary thin cable was used for the HV -ve line, and no safety diodes nor a grounding resistor.

http://www.gatesgarth.com/hv.jpg

My second question is should add any -ve line safety devices at the RF cabinet end of the line as well?

Thanks.
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Best regards, Chris Wilson.
K8AXW
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« Reply #1 on: November 11, 2012, 08:57:55 AM »

BASIL:  First of all, I'm far from an amplifier or HV expert.  However, with over 50 years in ham radio behind me, I can say with certainty that I have never seen these extensive safety steps you have taken.

On my homebrew amp I use HV wiring and HV connectors to connect the separate HV power supply to the RF deck as you are.  Nothing more.

I have a binder almost 3" thick full of amplifier plans and commercial amplifiers.  None have these elaborate safety measures.

Al - K8AXW
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2E0ILY
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« Reply #2 on: November 11, 2012, 11:22:49 AM »

Hi Al, thanks for the reassurance Smiley Being new to 5kV at nearly 2 amps I feel going a bit OTT with safety is not a bad idea Wink I got the grounding diodes and resistor idea from Ian White's site, from his Power Point presentation on HV power supplies and safety. I have put a copy at http://www.gatesgarth.com/hvpsu.pps

I have found his "In Practice" articles a Godsend in building this thing, and in general.
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K8AXW
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« Reply #3 on: November 11, 2012, 08:49:50 PM »

BASIL:  I can appreciate your concern.  Frankly, I wasn't aware of the 5Kv @ 2A rating.  I have never used or have seen amplifiers that use this kind of power so please defer to an expert on this.

I recall W8JI recounting his experience with HV that almost killed him. 
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G3RZP
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« Reply #4 on: November 12, 2012, 12:28:55 AM »

My usual practice is to use coax; the best connectors disconnect the centre pin before the cabl;e shield.
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K8AXW
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« Reply #5 on: November 12, 2012, 10:22:54 AM »

I use metal core "spark plug" wire rated at 50Kv.  My connectors are B&W as I recall.  Probably like what you're referring to Peter.  The connectors have a HV plastic shell with the center contact very well recessed.

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KB1SEL
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« Reply #6 on: November 14, 2012, 05:00:32 PM »

Yes
« Last Edit: November 28, 2015, 02:41:28 PM by KB1SEL » Logged
2E0ILY
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Posts: 143




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« Reply #7 on: November 15, 2012, 02:03:02 AM »

I would get rid of the .5 second delay on relay and use a soft start circuit like the one used in the al-1500. Which only allows the hard start relay to energize if their is no fault on the b+ side. I would also add a glitch resistor

Check out how I built my supply in a henry 2000d on amprepairguy.com. Which was and still is setup to run between  100-150 mhz. It originally had a 3 phase plate transformer. Safety stud type diodes from the b- to ground not yet installed. Still waiting on them to get here.


Thanks, I will take a look at that with great interest. To be honest I plagiarised the circuit I showed the link to from the Henry manual. I already have a proper soft start and glitch resistors on the actual supply I have built. I just kept it simple to show the area where I was wondering about the negative line and whether to add diodes. Thanks everyone!
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Best regards, Chris Wilson.
KC4MOP
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« Reply #8 on: November 15, 2012, 06:48:29 AM »

Be EXTREMELY careful with ANY high voltage....5KV @ 2 Amps is getting very serious and even an arc over will scare the %&*T out of you.
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K8AXW
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« Reply #9 on: November 15, 2012, 09:23:01 AM »

MOP:  Seriously, 5Kv@2A will cause more damage than you'll find in your underwear!
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2E0ILY
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« Reply #10 on: November 15, 2012, 09:46:30 AM »

Thanks, I am hopefully asking the right questions and I am taking great care. Without occasional mortal danger life gets a bit dull though Smiley 
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KB1SEL
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« Reply #11 on: November 15, 2012, 11:59:36 AM »

Basil are you using the stock transformer that came in the 2000d
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2E0ILY
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Posts: 143




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« Reply #12 on: November 15, 2012, 12:48:59 PM »

Basil are you using the stock transformer that came in the 2000d

Hi Scott. No, the unit came from a UK university and was for 50Hz three phase. There are some notes from an American ham on converting the US three phase PSU to run on single phase with a capacitive input filter, having removed the swinging choke. I tried this on the UK supplied unit with no success. I gave up and sourced a BIG single phase transformer and did my own rectifier array and capacitive filter boards. I have built the HV supply in its own cabinet, and I can switch a 30 Amp Variac in and out of the primary circuit, so for less demanding valves (tubes) I can reduce the plate voltage to suit. Hopefully it will not sag too much under load, I have no means of safely loading it up until I come to run the RF section into my dummy load. I am not quite ready for that stage yet. Are you running something similar?
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KB1SEL
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« Reply #13 on: November 15, 2012, 01:20:26 PM »

I have a bunch of Spare parts
« Last Edit: November 28, 2015, 02:40:47 PM by KB1SEL » Logged
2E0ILY
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« Reply #14 on: November 15, 2012, 02:10:57 PM »

Right, I realize who you are now, the amplifier repair man Smiley Yes, I have had a quick look at the Henry stuff, good to meet you! I'll take this off list, but suffice to say there's not much known about these here in the UK. I am planning single HF band for the RF section, and keeping the remote metering control panel. Aberystwyth University paid for a Kevlar sheathed 30 foot umbilical to run the control panel remote from the main machine, it's good when you are spending someone elses's money Wink I am using it to have the noisy and hot stuff out of the shack. I am keping the 3CX3000A7 tube, and have uprated the blower, which was a puny little thing. I realise about the Variac, the idea was to be able to use the HV supply on things with far lesser need than 5kV on the plate. I'll have to see how that goes, but for now it's switched totally out of the primary, so the primary is straight across the 240 volt mains. I'll e-mail some photos if you like? I have the original manual and some of the original paper work for it, thanks. I have next to decide about how to do the RF section. I intend to fire it up as it is, on 27MHz into my water cooled dummy load, to check the tube and everything else. Then I can't decide what band to put it on. I guess 10 meters is easiest. It appears Henry used various tuning circuits in the 2000D including variable vacuum caps. My unit has a brass slug tuned coil and a "flapper" type capacitor. I'm toying with a roller inductor and vac caps, but need to take advice (hint...) Smiley

Anyway, I am veering well off topic. Let me know if you'd like to see photos. chris@chriswilson.tv

All the best, nice to know someone else is using one of these beasties. I'd like to buy another RF section, actually....
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Best regards, Chris Wilson.
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