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Oct 12 2014

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1600 V DC – testing

Today I managed to put together three essential pieces of the HV power supply that I am preparing for the GM-70 and/or th GU81 projects …

I wired up together the following modules of recent making:
the HV rectifier board,
the HV filter board,
the HV lightbulb board.

After some initial cold triple checking (for bad connections etc),

After some initial luke-warm testing with a low AC voltage (sourced not from 230V AC mains, but rather from the secondaries of a 2x 12V LED transformer),

I finally connected the set to the real thing.

It works.  A supply of symmetrical +800 V DC and – 800 V DC, totalling for a nice 1600 V DC (give or take a few volts).

Here are the screen shots:

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The dual light bulb in front of the main HV transformers is series connected with the transformers.

It is a “last resort” of safety from making a brutal short circuit to the mains. If my “device” (whatever it may be) has some form of flaw or short circuit, then these “mains-sided” lightbulbs will glow.

Actually, they may also glow, after switch-on, for a few seconds, due to the current surge and the process of loading up the capacitor bank.

When the initial surge is over, I have a circuit breaker switch installed, a type B6 – (medium speed, 6 Amps breaker).  This I use to “bypass those “mains-sided” light bulbs if all is clear and things look “safe to proceed”.   Here, on the photos above, you see that they are not ignited. They are already bypassed.

What you do actually see is the set of 2x 1150V light bulbs glowing.  Actually, they are series connected GU-9 type ceramic sockets, 2x a set of five, series connected, with associated GU-9 type mini light bulbs. 230V / 28 Watts each. A small FR4 type board houses all ten of the sockets, with series interconnections made between them.

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As can be seen, I use only one half of the HV rectifier bridge, and one of the two HV filter banks for this test.  The boards are actually prepared for the future option of a dual mono style, two independent rectifier and filter bank sets.

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Some stuff on the dual transformers board (the chokes and the HV caps) are not yet wired up at this time. On the lower part of the screen, below the green dual transformer covers, you can see the “mains-sided-series-bulbs” bypass circuit breaker.

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Above – the “last bastion of short circuit protection” that I mentioned earlier. P1120085 b


The HV filter board with the HV light bulbs.   The board actually implements the Transformer-Chokes concept. Indeed, a sneaky one, as the whole choke winding is uniformly exposed to the high voltage of a given rail, but is not exposed to the “full” gradient of the inter-rail voltage of 1600V.

In other words: although the choke is operating at a high rail voltage, the inter-winding insulation may not necessarily be a high voltage one, hence allowing for a few extra turns of wire and a few extra percent of inductance per such core (which, as can be seen, I packed up to the extremes – that is the maximum amount of wire that could be fitted on the core and bobbin, without prohibiting the assembly of the core lamels). These small transformer chokes actually have about 4 Henries each, and are made with a wire diameter sufficient to transfer a current representative for a PAIR of output tubes. In other words: The path to possible push pull scenarios is open.

The fairly high inductance that was possible to achieve on these chokes is a side effect of the non-gap assembly of the core. The core of these chokes does NOT need any gap.  That is because the wiring topology used to interconnect these transformer-choke wirings is such that the net magnetic field resulting from DC current flow is Null. Zap. Zero. Nichts. Niechievo.  Since there is no DC magnetizing component, I have comfortably forsaken the gap. And hence the inductance increased significantly.

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The thing that keeps bugging me is why on earth does the rectifier board make that irritating buzzing sound? Maybe it is the loose ferrite cores on the legs of the diodes. Since they are buzzing, that means that indeed, they have some work to do. Now I only need to convince them to do it quietly. Maybe some super glue or putty will do the trick. Just Junk some guey upon those diode legs and those ferrite cores. Should do the trick.

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The photo above was done some 30 s. after I disconnected the mains. Indeed, the light bulbs provide a visual as to the safety related to poking your fingers into the setup. It turns out that at best wait one or two minutes before even considering putting your fingers in there.

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