Tube Amps / Music Electronics
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|4/4/2005 7:23 AM|
||put standby before or after 1st filter?|
Can someone explain the relative pros & cons of putting the standby switch after the first filter, as in Fenders, or before it, as in Marshalls?
And if it makes any difference, assume there's a 5U4 rectifier. And an HT fuse.
|4/4/2005 8:22 PM|
Everyone will come up with a rationalization for why their method is better, but it just doesn't matter. You can decide if you want the caps to stay charged or not, or some but not others. Who cares?
In the off position, B+ doesn't get to all its destinations, and ON it does. That's all. I care a lot about safety, so I always assume caps are charged until I know different. As to voltage, there will always be a high voltage on one side of the switch and not the other. It is all lethal no matter how you do it.
The point is to silence the amp without having the tubes cool down. You can remove B+ from them altogether or just from the screens, either works. You can do what some amps do - short the output tube grids together. All of those work
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|4/5/2005 1:43 AM|
The Silvertone 1484 just shorts the output tube grids together, but it doesn't work completely, as when it is in standby you can play and hear it as if it was going through a tinny little speaker in a headphone. Actually a cool effect!
|4/5/2005 8:02 AM|
The only technical things I can think of are
1st cap always charged style:
pros - possibly less current surge when you flip to play
cons - cap voltage will rise significantly when you flip to standby
all caps discharge style:
pros - possibly safer to work on, no stress on cap during standby
cons - more surge stress when you flip to play
|4/5/2005 9:37 AM|
[QUOTE]1st cap always charged style:
pros - possibly less current surge when you flip to play[/QUOTE]
I thought so too - so maybe that would be less likely to make a thump sound or blow the HT fuse when I switch to play. I think if I put bleeder resistors on both the 1st and 2nd filters, then the pros & cons would balance in favor of doing it that way.
Maybe Enzo's right that it doesn't really matter, but each way of doing it is just as easy as the other, and I'd like to have some idea why I'm picking one over the other no matter how minor that reason may be.
|4/5/2005 9:59 AM|
I've heard of a few problems with the standby switch actually wearing out after time due to arcing... more likely to occur if the switch is before the first filter caps. I've never experienced this, as I play Fenders. So longevity of the switch itself may be another minor consideration.
|4/5/2005 10:49 AM|
There's another alternative which will eliminate voltage stress on the switch. You can lift the cathodes of the power tubes from ground. This will leave ALL caps charged and the voltage differential across the switch will be just a few volts.
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