Hello all,
In the process of building a tube rectified 2-box 26 preamp and I'm planning to have two switches on the power supply box, one for filament power and one for B+. There are separate filament transformers for each 26 tube, while the rectifier tube gets its filament supply from a winding on the power transformer.
The question: Since the rectifier tube is needed to supply the B+, does its filament need to be switched with the other filaments, or should its filament be switched on as the B+ is switched on (as the main power transformer is powered up)? I can think of arguments for both.
If the rectifier filament needs to be switched with the others, I'd need to buy another filament transformer, whereas the other alternative is already covered.
Any help is greatly appreciated.
In the process of building a tube rectified 2-box 26 preamp and I'm planning to have two switches on the power supply box, one for filament power and one for B+. There are separate filament transformers for each 26 tube, while the rectifier tube gets its filament supply from a winding on the power transformer.
The question: Since the rectifier tube is needed to supply the B+, does its filament need to be switched with the other filaments, or should its filament be switched on as the B+ is switched on (as the main power transformer is powered up)? I can think of arguments for both.
If the rectifier filament needs to be switched with the others, I'd need to buy another filament transformer, whereas the other alternative is already covered.
Any help is greatly appreciated.
I could go with just one switch, but I thought it might be useful to be able to warm up the filaments before applying B+, especially when using DH rectifiers. I plan to evaluate a wide gamut of rectifiers, both DH and IDH. I will be the only person ever turning the preamp on (in my lifetime!) and the switches will be labeled and in order from left to right.
Philosophy aside, if I want to have two switches, should the rectifier filament be switched with the other filaments or with the B+?
I've been planning this preamp for months, and my initial thoughts were to switch the rectifier filaments with the B+ because the rectifier supplies the B+, after all...but months of thinking about every detail made me wonder if that was actually correct, So I thought I'd ask to be sure.
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Philosophy aside, if I want to have two switches, should the rectifier filament be switched with the other filaments or with the B+?
I've been planning this preamp for months, and my initial thoughts were to switch the rectifier filaments with the B+ because the rectifier supplies the B+, after all...but months of thinking about every detail made me wonder if that was actually correct, So I thought I'd ask to be sure.
.
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By the way, if it matters, the PS is choke input, with only PP film caps.
So Osvaldo, you're saying it would be safer to switch the rectifier filament at the same time as the B+, correct?
Definitively yes. Yes, for me, obviously.
Although some reserves can be made. In my project, (search in this forum), if the rectifier tube has fast hot time (like 5U4), the initial current surge I believe may be dangerous. My project include a 3DG4 that has a longer hotting time, and also 12Hy choke input. The filaments of all set but that of this rectifier are powered simultaneously, and independent of the +B. 3DG4 filament is taken from +B trafo, so only it warms when +B is switched on, before normal amp heating. All trafos are toroidal hand wired.
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Thanks for the reply! So the rectifier filament will get switched on with the B+, as originally planned.
Sometimes having too much time to think just muddles the mind...
Hi Kay. You possibly are right. My opinion was only this, a opinion. I prefer to start heater and +B at the same time.
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
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".
Best regards
Michael
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.
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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