tube Heating 6.3V and variac (for a HV PSU)

[JacquesBBB]

Dear All,

I just got a  high voltage regulated power supply of 1971 (1200 V, 10-80 mA). Mostly with tubes.
I would like to revive it but with cautious.

I have not yet checked anything,  but I wonder about the heating voltage requirement of 6.3 V  ± 0.6 V  of a  8068 tube
if ever I use a variac to start slowly the PSU.
As the 6.3V is obtained through a direct transformer from the main,  the voltage will be much lower than 6.3 V.

Is it still advised to use a variac to reform the capacitors  by powering at a much lower voltage than the 220 V for which  the PSU is designed ?


Thanks for any hint.

[SeanB]

No problems there, the lower voltage means the heater is not going to emit as much, and will limit the current flowing through the diode. It will still emit even if it is not glowing, but will be enough to charge up the capacitors in the circuit to reform them. Start first though by checking all capacitors are not shorted, leaking electrolyte ( white deposit by the rubber bung) and that the tubes still have a shiny getter inside ( no white deposit on the inside of the glass, silver gray to brown is fine) and the transformer is set to the correct line voltage.

[JacquesBBB]

Thanks for this advice.

I will look to all the caps before powering anything, as well as on all components and verify connections, but I will only be able to do this on next week end. Meanwhile,   it  is a useful thinking time to avoid  doing anything wrong by excess of precipitation.

What would be the recommended  voltage to start with the variac  for the capacitor reform, owing that the normal  voltage of the unit is 220 V.

I will post pictures later on, but I can already post the schematics which is the only (and most useful) piece of information I have for this PSU.

[SeanB]

HV transformer 4564 will not get power till the mains is about 140VAC, because of the current trip relay, so you probably want to make a dim bulb tester to do the initial reform, with a temporary connection across those 2 relay contacts so as to power the HV transformer 4564. I would start with a 40W lamp in the dim bulb, and start at around 50VAC for a half hour or so and then power off and check for warm transformers or capacitors. Then if all is fine go to 100VAC and do the same. Then for the third step remove the temporary connection across the relay and then apply 150VAC and press the HT start button and the relay should turn the transformer on.  If no hot other than the valves ( they should all have a faint heater glow at this voltage) then you can go to the full 220VAC and do a check of operation with the lamp still in place. It will probably be glowing dimly at this point.

[JacquesBBB]

HV transformer 4564 will not get power till the mains is about 140VAC, because of the current trip relay, so you probably want to make a dim bulb tester to do the initial reform, with a temporary connection across those 2 relay contacts so as to power the HV transformer 4564.

Thanks for this detailed information, but  I am missing some background to understand properly.  What is a "dim bulb tester",  and  what  should be the proper connection to make ?

[sync]

I only see one electrolytic cap (3300uF 25-30V) in the schematic. The other caps are non polarized. Maybe the high voltage caps are oil paper type. AFAIK they can't/needed to reformed. If you are unlucky they contain PCBs (http://en.wikipedia.org/wiki/Polychlorinated_biphenyl). That stuff is evil.

Also there are no bleeder resistors across the high voltage caps. They can hold the charge (voltage) for a lot time (days till months). Even if the power supply is disconnected from mains it is very dangerous.

[oldway]

Be carefull because it is not a voltage regulated HV power supply but a 1200V power supply with ajustable current limiting.
Output voltage IS NOT ajustable ! It has a fixed output voltage (with no voltage regulation, only current limiting) of 1200V ...

I wonder what such a power supply could serve.
It is only extremely dangerous, even deadly.
Better stop with this !!!!!!

[SeanB]

Output voltage is adjustable, using the 806 pentode as a triode to regulate the negative rail.

The dim bulb tester is a 60W incandescent lamp ( 220VAC tungsten filament one, not a CFL or led lamp, though you can use a halogen lamp here) in series with the mains supply, so that if there is a large current flow for some reason, then the lamp will light to indicate this, and the increased resistance of the hot lamp reduces the chances of damaging other components.

[oldway]

Output voltage is adjustable, using the 806 pentode as a triode to regulate the negative rail.

I do not agree.
Only the cathode current of 806 is regulated, not the output voltage.

I started learning electronics with vacuum tubes, I made a lot of audio amplifiers and other vacuum tubes stuffs in the sixties.

[SeanB]

There is a pull up provided by the meter, so the cut off 806 will act as a voltage divider, there is enough negative drive available to bias it to cut off with that as a load.

Would not class the output terminals as touch safe under any circumstances, it just will be best to treat them as being always at 1200V, including the negative terminal. But it will provide 50mA at an adjustable voltage from probably 100V to 1200V.

[sync]

Where is the voltage adjustment? I don't find it in the schematic. This looks like an adjustable constant current source for me.

[oldway]

There is no output voltage regulation, nor voltage adjustement, only a current limitation from 10 to 70mA.
I think SeanB does not understand how this schematics works.
It's a vacuum tube schematic, perhaps he is too young to know how it works.

But it will provide 50mA at an adjustable voltage from probably 100V to 1200V.

Absolutly wrong...such wrong information is very dangerous because JacquesBBB could think there is a low output voltage and try to measure it with multimeter.

But output voltage is always 1200V...!!! This exceed max. input voltage of most of the multimeters and may be lethal.

[sync]

I only know little about tube circuits.I have a question about the schematic. What is the purpose of the left PM07. It's a current sink, right? But what it does in the circuit?

[oldway]

This is an ajustable current sink intended to make calibration of the current limitation.
Pot MP2a (50k) has to be ajusted for current limiting at 10mA when current selector is on position 10 mA.

[JacquesBBB]

Thanks to all for your information and your concern.

I am aware that this is a PSU with voltage of 1200 V at no load, but with adjustable current from 10 to 70 mA.

It was used for some scientific device. Maybe some photomultiplicator tube. I will have to check. I will be very buzy the two next days, but will post some pictures this week end.

[TimFox]

The schematic seems to be of an adjustable constant-current source with a high compliance voltage.
This can be dangerous, since when the load is disconnected, the output will go to 1200 V (or so).
My Fluke voltage/current calibrator has an extra control to limit the maximum compliance voltage.
(A current-limited source is normally a voltage source with a non-precision adjustment of maximum output current.)

[JacquesBBB]

This is a rapid picture of the item  ( right now in my trunk) .
More to come this week end.

[oldway]

Another safety tip:

The insulation between primaries and secondaries and between secondaries and earth should be checked.

In the event of insulation failure, very dangerous high AC voltage can exist between the dc output and earth.

[JacquesBBB]

As promised,

here are a few pictures of the outside and inside.

[JacquesBBB]

following ...

[JacquesBBB]

I have checked the caps,

they are well within specs. I will probably try to power it without changing any of the caps, as  I do not see what could be gained by changing with new ones.

Here is an example for an electrolytic cap.

[SeanB]

Now we have pics.... Looks like it was made for an avionics test bench, probably by SNECMA. Layout, wiring methods, placement and component choices all look like their style of engineering, along with the case and the connectors.

The capacitors will likely all be fine, they are all made to milspec standards, and are ultra high reliability, aside from those white Precis foil types, which are known to sometimes fail. I have a few of that same series in a box somewhere. The big foil HV caps will be fine, they are pretty bulletproof. The valves all look OK, though you might find that the 806 tube will glow for a while at startup, it is slightly gassy.

[T3sl4co1l]

Probably need to reform the electrolytics (take them up slowly, watch for heating), but otherwise yeah, looks great

Tim

[JacquesBBB]

Thanks for the comments Sean, Its really nice to have some feedback, as I am really new to this game.

Concerning the constructor, its not SNECMA, but Siemel, which was a small company  in the south suburb  of Paris,
specialized in HT and THT  power supplies.
(see http://retro-forum.com/viewtopic.php?p=70259&highlight=) .

These were designed for scientific tubes. Maybe to power some hydrogen tube.

I  will have to wait   in order to power it, as  I am missing the power plug on the rear panel.

As I have another HV PSU with the similar plug, I will try to get one.
https://www.eevblog.com/forum/projects/any-reference-for-these-power-plugs/msg636072/#msg636072

[oldway]

I personally do not see any interest to power on this power supply.

Output voltage and current are extremely dangerous.

Why take unnecessary risks?

As it is designed, it has no possible application in the amateur field and it is a completely outdated design for professional use.

It is a museum piece, no need to turn it on.