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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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23rd Jan 2018, 1:06 am | #41 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Wanted: Circuit for HV PSU
There are a few complications when it comes to estimating the voltage at TP1. These include
1. When the transformer is off-load it will supply more than 300-0-300 on the HT secondary 2. There will be some forward voltage drop in the rectifier (it may be pretty small when the current is low) 3. There will always be some current drawn - you'll have a few milliamps flowing through the 56k and the 85A2 and you'll have some more (maybe only 1-2 mA ?) flowing through Rtop+47k+Rbot. Cheers, GJ
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28th Jan 2018, 11:36 am | #42 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
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Re: Wanted: Circuit for HV PSU
Hi Guys,
I have uploaded a revised circuit for my simple PSU project. Again, I would welcome any comments, tips etc. I have included a cathode follower after the 85V gas stabiliser as suggested. Would it be better to strap the two EL86s as triodes? I intend to start by building the left hand side of the circuit and to measure the voltage at TP1 for varying loads which should make calculations for the right hand side of the circuit easier and/or more realistic. Many thanks and regards
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Eddie BVWS Member. Friend of the BVWTM |
29th Jan 2018, 2:56 am | #43 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: Wanted: Circuit for HV PSU
Hi Eddie, a current limit circuit may be useful (better with semiconds), but not essential.
Ed |
29th Jan 2018, 4:47 pm | #44 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Wanted: Circuit for HV PSU
Suggestions:
1. Add suitably-rated mains I/P fuse and DPDT switch. 2. Add fuses in series with each rectifier anode or one in the cathode of the rectifier. (You have a choke I/P filter, so the surge current to the filter cap. is via that choke. That should prevent that from fuse from 'switch-on blowing', which couldl occur with a pi-filter). 3. Metering the O/P: add voltmeter and ammeter. 4. On / off switch for O/P and indicator bulb / light / neon. Fit indicator on load side of switch; fit O/P voltmeter on source side. A glance at the voltmeter will tell you how many volts are 'available', prior to connecting the load via the switch. The indicator will tell you when the volts are actually applied to the load. 5. Fit fuse - or a suitable current-controlling circuit - to the O/P. Al. |
29th Jan 2018, 5:16 pm | #45 |
Octode
Join Date: Mar 2006
Location: Watford, Hertfordshire, UK.
Posts: 1,270
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Re: Wanted: Circuit for HV PSU
The attached circuit is of my ancient Brandenburg Stabpak A50. It seems to break some of the rules already raised, particularly the high anode voltage for the EL86. But I post it as an example of a commercial unit. It does work fine but has a limited variable voltage range.
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29th Jan 2018, 6:53 pm | #46 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
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Re: Wanted: Circuit for HV PSU
Perhaps I've over-looked a few things or maybe my arithmetic is in error, but I don't like the look of that design.
1. The rectifier reservoir cap. is rated at 500 v. Yet the cct. diag. states that it has 490-v. across it - presumably at no load. (My inference is obvious. ) 2. That 490-v. will drop a bit when current is drawn by the load: O.K. Let's assume that at a load current of 25 mA and a Vout of 200-v, that voltage drops to 450-v. There will be 250-v. dropped across the EL86 and it will be passing the 25 mA. So the EL86 anode will be dissipating 6.25-watts. For same 450-v. as above, but for 35 mA O/P at 200-v, that dissipation will be 9-watts. The EL86 has a max. anode dissipation of 5.6-watts. The O/P fuse is 50 mA. At that lowest voltage setting of 200-v., by the time the load current has got anywhere near that 50 mA, the EL86 will have fried. The EL86 will protect the fuse! Al. |