I'd be pretty impressed if I managed to get the relay to chatter, given that turn-off voltage is typically about 10% of nominal coil voltage.
As to the timing accuracy - it really kinda doesn't matter. The cathodes of the tubes need time to heat up before the amp is useful, and the exact warm up delay varies between different tube manufacturers. Making it arbitrarily long should suffice.
Yeah, but then that digs into your usability range -- how come everyone else's rig is ready to go in ten seconds and this one takes 40 seconds after pulling it out of the trunk on a cold day? It's so inconsistent and...
Obviously you know your customers better than me, so it's up to you (and them) if that's any bother.
My mind also wanders to ever-more-efficient methods, like... you could put a 120VAC coil in series with the FWB, solving several problems at once (less voltage to drop across R or C, transient protection thanks to substantial coil inductance), then use the stuff after the bridge as a modulated load. When power is applied, it starts at high impedance (100kohm+?), and the relay stays off. After the time delay, its impedance drops (0 to ~kohms), supplying current to the relay. But what about the voltage range? It's a constant current sink, so it doesn't overvoltage the relay. Power dissipation can be lower, on account of the relay coil voltage being closer to mains voltage. (Well, maybe; AC coils may need more current than their DC counterparts, which wouldn't be so friendly to the current limiting circuit.)
But whatever... just an amusement, nothing worth looking at unless you were making 100k of them.
Oops, sorry, should have kept the component labelling more consistent. Note I've lowered R2's power rating from 10W to 5W.
Fuse F1 is also for transformer protection. It's a nominal value for 100V/120V operation. F2 is a higher rated non user-accessable fuse because musicians are idiots who will do anything to finish a gig, including wrapping blown fuses in chewing gum wrappers or aluminium foil, or replacing them with iron nails.
Yeah, I get that need.
A separate (and much smaller) fuse for the delay circuit would be the trick.
Not sure I follow why you say that, the CRC pi filter just allows the use of smaller value caps.
Hmm, but you've still got 100uF in there, so you've got 110uF total..?
Remember the power isn't delivered in spikes like it is for a C-input filter; the series dropping C, with the FWB, makes the voltage nearly square-wave, and the current comes in humps. (This is all obvious on the simulation of course, and you can see just how much filtering is actually needed, whether it's 100uF, or more or less.)
I often see that thrown about, but noone was ever able to point me to any reference as to why. I realise that up until recently manufacturers weren't making any TVS diodes they recommended for AC power lines, but that hasn't been true for a while now. Bourns Littelfuse.
Hmm, ~70V devices? What good is that...
Lovely ratings on those, though! It takes a metric shitload of silicon to stomach 15 kiloamperes.
Speaking of which...
http://www.digikey.com/product-detail/en/bourns-inc/PTVS10-380C-TH/PTVS10-380C-TH-ND/5053079So if you get one, that by the appearance, is probably a literal stack of the single unit parts (which are, themselves, probably anti-series pairs of dies) -- it's expensive enough to buy a matched quad of 6L6s!
Also, on the other hand, something a little worrying... no energy rating. There's a temperature derating, but no way to guess what it can offer for waveforms other than the 8/20us surge. What if I need to test 10/1000us surge? What if I have a high voltage application that occasionally generates wicked ESD (like, accidental strikes from a 50kV+ source).
Given that MOV's progressively degrade, and often catch fire or explode leaving char and ash all over the inside of equipment (I'm a repair technician, I see this a LOT, I've even seen a number of times equipment that had a proper mechanical switch, and yet the MOV was connected across the line BEFORE the switch, so was subject to all transients 24 hours a day if it was left plugged in but unpowered!)
Yeah, so realize that you've seen all the shitty designs: too-small MOVs, in the wrong places, no protection, no graceful failures, just smoke and shit.
Suppose, then, that it is possible to use MOVs, responsibly, and to get long life.
Much longer life than the $100 TVS will provide, and at a tiny percentage of the cost!
An MOV with the same energy rating as that TVS is $0.60 or less. It won't take /that/ big of a surge forever, no -- but a larger one (a buck or two) will last decades.
Tim