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Old 24th July 2012, 06:48 PM   #11
mvd is offline mvd  Germany
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Quote:
Originally Posted by DF96 View Post
Why not have one switch? If you need sequencing (which I doubt) then this should be automatic, otherwise you will sometimes get it wrong.
Maybe one can find a Mains-Switch wich has 3 Positions, like "Off", "Preheat" and "On".
Building it in this way nothing can go wrong.

There are many round-switches wich have more than only 2 positions.

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Old 24th July 2012, 06:50 PM   #12
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Quote:
Originally Posted by mvd View Post
Maybe one can find a Mains-Switch wich has 3 Positions, like "Off", "Preheat" and "On".
Building it in this way nothing can go wrong.

There are many round-switches wich have more than only 2 positions.

Best regards
Michael
Excellent idea !!!
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Old 24th July 2012, 06:57 PM   #13
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Like this one - New AC Selector Switch ? Just noticed the out of stock.
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Old 24th July 2012, 07:09 PM   #14
mvd is offline mvd  Germany
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Originally Posted by CharleyW View Post
Like this one - New AC Selector Switch ? Just noticed the out of stock.
Yes, this looks nice.

BUT, i think it has to be a "make before break" switch, the same principle as in a stepped attenuator. Otherwise the heater voltage will have a break for a few milliseconds while you switch from "Preheat" to "On".

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Michael
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Old 24th July 2012, 07:13 PM   #15
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Why not a car with 2 steering wheels, one per a front wheel?
My wife would like that.
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Old 24th July 2012, 07:18 PM   #16
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My wife would like that.
So, 3-position switch would not work. You definitely need 2 separate switches. Like missile launch stations had 2 buttons locked each by own key. By the way, I used a key lock in one of my amp prototypes. The amp can be locked so kids can't touch hot tubes, break glass, be electrocuted by 800V on anodes.
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Old 24th July 2012, 07:18 PM   #17
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And what about a temporized relay?
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Old 24th July 2012, 07:24 PM   #18
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Or building the rectifier with damper-diodes wich give you a nice warm-up time from 20 to 30 seconds.

For a preamp the duo-diode 6BY5 from RCA would be a good choice.

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Michael
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Old 24th July 2012, 07:30 PM   #19
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Semiconductors are more convenient than tubes for power supplies. For slow start I use voltage stabilizers with positive feedback by current that works until the regulator starts stabilizing voltage. It brings up voltage very slowly with no load. When tubes are hot and start drawing current it increases voltage with higher speed, but slow enough to avoid surge currents due to initial charging capacitors in the amp. Smoothly and graciously.
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Old 24th July 2012, 07:32 PM   #20
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I personally stronger dislike mixin' sand and glass. SS for SS and VTR for tube amp. In my regenerative AM receiver, ss diodes irradiates harmonics. A pretty 6X4 was the solution.
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