experiments with tube suggestions

[xazrules]

Hi vintage people! after some succesful builds  that i've found here i'd like to make some experiments with tubes.
But what i wonder is how do you breadboard or experiment with high voltages? i have a lot of fun come with my own circuits with transistor on the breadboard, but i'm a little bit worried about my safety with higher voltages, don't you have some insight on how to set up a mad scientist workbench?

thank you vey much for your time!

Best regards

E.

 

[ruffrecords]

I normally use a separate power supply when experimenting. It has an output socket so you can easily disconnect your experimental rig and be certain there are no lethal voltages being fed to it. However, you do need to ensure any HT smoothing capacitors in the experimental rig have a discharge path because you can still get a shock from them even after the power supply is disconnected.

Cheers

Ian

 

[JohnRoberts]

Very carefully and remember to keep one hand in your pocket.

JR

 

[dmp]

I've done some searching for this also and have only seen homemade prototyping boards. I haven't seen something you can buy ready to go.
I have a old wood cutting board (14" by 20") that I'm planning to use, mount tube sockets and some kind of screw terminals.
Agreed on having good habits when working with high voltages.

 

[Tubetec]

Back pocket might be  safer  for a number of reasons also  , especially as we get on in years  ;D

 

[xazrules]

Yes the left hand always in the pocket, and yes the only solution seem a wood board with various tube socket installed and wires that go in  the breadboard. and what about the psu? isn't there some project about a variable regulated HT psu around?
Ian i've just finished experimenting with your universal HT psu, i'm using a transformer with the secondary rated at 240vac 0,13a but at the output i've 280vac and at the output of the regulated DC i've 420 vdc without load, i've used 400v rated 220uf caps, is there a method to lower the voltage post or pre power transformer? or once i've a load connected the voltages lower at least to 300vdc by themselves?
i've also experimented with and without bleed resistor and without it, it would take days to discharge all the caps! so always use a bleeder, checked  8)

Thanks!

 

[ruffrecords]

Ian i've just finished experimenting with your universal HT psu, i'm using a transformer with the secondary rated at 240vac 0,13a but at the output i've 280vac and at the output of the regulated DC i've 420 vdc without load, i've used 400v rated 220uf caps, is there a method to lower the voltage post or pre power transformer? or once i've a load connected the voltages lower at least to 300vdc by themselves?
i've also experimented with and without bleed resistor and without it, it would take days to discharge all the caps! so always use a bleeder, checked  8)

Thanks!

It is a very simple+ unregulated HT supply. If you included the heater elevation resistors then they should act as a bleed resistor to discharge the caps reasonably quickly.

Because it is unregulated, the output voltage varies with the ac input voltage and the load at the output. In addition, the output of most transformers is specified at the rated load. At lower loads the voltage will be higher. This explains why your 240VAC rated transformer outputs 280VAC when unloaded. The output of the power supply when unloaded will reach the peak value of the ac input. This is 1.414 times the ac voltage so for 280VAC this is 396 volts so the 400V you see is about right. To be on the safe side you should therefore use 450V rated caps in the supply

Class A tube circuits are not overly bothered by the exact HT voltage they are provided with. As long as it is over 250V they are usually quite happy.

If you want a regulated supply that drops like a stone when turned off even with no load I would highly recommend this one made by International Power:

https://www.mouser.co.uk/ProductDetail/international-power/ihb250-01/?qs=0xCm9DOQnC5apaiylMDitA==&countrycode=GB&currencycode=GBP

and available from Mouser.

Cheers

Ian

 

[xazrules]

thank you very much Ian, 70 euro for a ht psu seems a bang for the buck!
what if i place a series resistor before the diode bridge?

 

[ruffrecords]

thank you very much Ian, 70 euro for a ht psu seems a bang for the buck!

Yes, I think it is very good value for money. Pity they do not do ne with a higher current output.

what if i place a series resistor before the diode bridge?

If the power supply is unloaded, adding a resistor before the bridge will make no difference at all - the output will still reach the peak of the ac input voltage. It will reduce the output voltage when the supply is loaded. just like the ones between the caps do already.

Cheers

Ian

 

[xazrules]

clear, is a good technique to place two resistors after the two windings like in the pic attached? so once loaded the first cap sees a lower voltage, at the moment i haven't a 450v rated cap.

 

[ruffrecords]

clear, is a good technique to place two resistors after the two windings like in the pic attached? so once loaded the first cap sees a lower voltage, at the moment i haven't a 450v rated cap.

That might possibly be OK for use in a guitar amp but nor really a good idea for a bench supply. I am not really quite sure what it is expected to achieve.

Cheers

Ian

 

[xazrules]

Thank you Ian! Once settled i'll check out the psu from mouser