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Old 9th November 2006, 05:30 PM   #1
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Default on-off switch position in PSU

Where's the best (safest??) place for an on-off switch in a PSU. I will use a Hammond 269AX transformer feeding a cap-input choke system yielding around 300V at 30mA. A separate tranny will be used for 6.3VAC heaters.

I am thinking of making the PSU in a separate chassis to the Aikido preamp. However, I would like to use a delay octal tube to allow the heaters to run prior to the HT.

If I place the tube delay in the preamp to switch on the HT at the B+ end of the PSU, AND have a switch on the actual PSU to switch on both transformers simultaneously, will there be a problem with having the HT powered, but open (switch-off) at the preamp end???? Does this make sense?

Of course, it seems that cathode stripping is not too much of a problem at these lower voltages, but if I can avoid the risk for relatively few dollars, then why not go for it????

Charlie
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Old 9th November 2006, 05:38 PM   #2
Nordic is offline Nordic  South Africa
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A simple NE555 timer using the 6.3V supply combined with a relay to delay completing the power to the other transformer is cheap, quick and less then $5.

Mains power gets connected to the 6.3V Transformer with a switch... after the switch it goes to the middle leg of the relay's output side as well... from where it can not get to the other transformer, which is connected to the other leg of the relay, until the realy is activated by the timer.

So throwing the switch starts the heaters, and the timer, and then only when the timer has run, it switches on the plate supply.
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Old 9th November 2006, 05:39 PM   #3
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Nordic,

Do you have a schematic for this???

Charlie
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Old 9th November 2006, 05:54 PM   #4
Nordic is offline Nordic  South Africa
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Here, original credit by Franz Gysi

Attached is PCB, for 6.3V LM317 based regulator connected to the relay , the red wires are just wires not traces... in eagle, click ratsnest icon to fill in ground plane automaticaly....

it has outputs for the heater and the mains cable goes to middle row of relay switching pins... On my amp I connected a neon lam over the two legs of the realy that is connected until it is powered to show its warming up... then when the timer has run the relay switches the power from the neon lamp to the other transformers in my setup.
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File Type: gif delay.gif (2.0 KB, 196 views)
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Old 9th November 2006, 06:16 PM   #5
Nordic is offline Nordic  South Africa
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lets try again
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File Type: zip relaydriverboardfile.zip (4.8 KB, 39 views)
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Old 9th November 2006, 06:41 PM   #6
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I don't seem to be able to open the "relaydriverb.brd" file. What kind of file is it?

Charlie
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Old 9th November 2006, 07:09 PM   #7
Nordic is offline Nordic  South Africa
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eagle board file C17 is 47uF / 16V
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