Delay B+ using relay?

[ryuji]

i have a SSR rated at 3-32v control voltage and 25 amps of load(i know extremely overkill, im interested in using it because its solid state)

i know most of you people go through all sorts of trouble making delay timers etc. But my idea is as i have a 6.3v heater system using a linear current limited power supply, i could perhaps use a voltage divider with equal resistance on both resistors, and then feed the divided voltage into the relay. the relay will catch when the voltage on the heaters gets warm enough that my recifier tube startup delay will be long enough that it will be all ready for conducting

anything wrong with my logic/thought process?

[KatieandDad]

Why not just use an LM317 in SLOW START circuit as per the datasheet.

For heaters you can even use it as a CCS with SLOW START.

No chunky relays.

This is how I approached the problem with my Borbelly clone.

The LM317 slowly applies heater power to the valves, then after approximately 30 seconds the B+ is applied to the HT rail.

[Wavebourn]

Originally Posted by ryuji

i know most of you people go through all sorts of trouble making delay timers etc.

Most of us don't understand why it can be needed.

Soft start - yes. But abrupt B+ application on hot toobs when interstage coupling capacitors are discharged? Hah...

Search for soft start, inrush current limiting, we discussed such matters here many times.

[ryuji]

i already have soft start actually, i use a tube rectifier. but it doesnt quite take long enough to warm up and the tubes dont conduct for 5 to 10 more seconds after rectifier gets hot enough to light up my voltage regulator tubes. linear supply bring up the filaments in about 60 seconds total, which is probably nice for them anyways

so what im really aiming for is a delay isnt it?

[Wavebourn]

Originally Posted by ryuji

i already have soft start actually, i use a tube rectifier. but it doesnt quite take long enough to warm up and the tubes dont conduct for 5 to 10 more seconds after rectifier gets hot enough to light up my voltage regulator tubes. linear supply bring up the filaments in about 60 seconds total, which is probably nice for them anyways

Why?

It was safety measure for radar output tubes that started generating high power RF energy when parts of their filaments started emission. As the result such parts were getting even hotter, so each time the tube was powered on, tiniest parts of filaments evaporated faster than the rest of filament. But such effect do not exist in audio amps.

[ryuji]

Originally Posted by Wavebourn

Why?

It was safety measure for radar output tubes that started generating high power RF energy when parts of their filaments started emission. As the result such parts were getting even hotter, so each time the tube was powered on, tiniest parts of filaments evaporated faster than the rest of filament. But such effect do not exist in audio amps.

Ah i think i understand what your getting at now. your saying its just fine for the tubes to have HT come up before the tubes are even close to conducting.

Im a little bit worried about my filter capacitors too tho, there rated for 500v but i imagine 10 or so seconds at up to 565v isnt going to internally heat them enough to kill them

[Wavebourn]

Originally Posted by ryuji

Ah i think i understand what your getting at now. your saying its just fine for the tubes to have HT come up before the tubes are even close to conducting.

Yes, and manufacturers of tubes thought similarly when specified max voltages on cold tubes higher than on hot tubes: they expected them to heat up then sag power supply.

Imagine, when interstage coupling capacitors charge initially through grid leak resistors positive voltage on grids don't cause grid currents. But charging through conducting go cathodes grids they cause significant stress to tubes.

[ryuji]

Ah so it has the side-benefit of allowing my coupling capacitors some time to charge up pretty much all the way, makes sense. so in fact the timing of all my stuff is rather ideal, my bias supply comes up near instantly, then the b+ about 30 secs or what feels like it later, and then the filaments some time later

[Wavebourn]

Originally Posted by ryuji

Ah so it has the side-benefit of allowing my coupling capacitors some time to charge up pretty much all the way, makes sense. so in fact the timing of all my stuff is rather ideal, my bias supply comes up near instantly, then the b+ about 30 secs or what feels like it later, and then the filaments some time later

There is a saying, "Better is enemy of Good"

[payitforwardeddie]

I've always believed in KISS. Keep It Simple, Stupid. I'm sure the valve designers (and amp designers) had this in mind, years ago, before transistors blew in.