^if you are going to use a relay to switch out the NTC, then you might as well use a power resistor say 20ohms/50watts....
Not in my case because you need the voltage over the thermistor to decrease and the heater voltage to increase, or it wont work. Heres a schem:
Edit: Note that when rectifying 6.3volts AC you can get about 9V DC, so a small resistance or perhaps a LED might go in series with the relay. Most relays handle quite large variations in coil voltage and I havent had any problems so far. If I remember correctly the relays I use have 5volt coils, but I cant remember if I have anything in series. Man my memory stinks...must be all the solder fumes🙂
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then why short out the NTC? they are meant to stay in-circuit, when heated up they are very very low resistance anyway...
Yes ! NTC has very no resistance. It seem to be no need to use a relay to short it. Why I short it ? Due to has a Self recover fuse series with it. This self recover fuse use only at startup tube testing procedure to avoid ultra high current burn parts at startup. Power tubes can protect by u_Controller but have a very short time gap can not protect.
Also, even tho they have relatively low resistance when hot, they still drop almost a volt, so I end up with just a slightly low heater voltage. (I've tried several different types and they all seem to drop 0.7-1volt when passing anything from some to max current).
time delay
Hi I bought a time delay of electric sophy for my 300b amp
I connect to + B 435 volt high voltage interrupt and after
30 seconds in and hits the speakers and can not find another way
One could insert something in the court where it could relay or put
the grinder is 5U4G/5Z3.
Hi I bought a time delay of electric sophy for my 300b amp
I connect to + B 435 volt high voltage interrupt and after
30 seconds in and hits the speakers and can not find another way
One could insert something in the court where it could relay or put
the grinder is 5U4G/5Z3.
I use damper diode tubes. You can get the Russian 6D22S with the top cap good for 300mA continuous and the cathode can be 600V over the heater. It has a slow start up of about 30 seconds. It is much easier to switch its heater voltage if you want a longer delay.....
I use a solid state bridge-cap-coil-cap-damperdiode-cap=B+.
I use a solid state bridge-cap-coil-cap-damperdiode-cap=B+.
Although this is an old thread it is still as valid today as all that time ago.
Rather than using NTC's in series with the filaments one can use NTC's in series with the primary of the transformer, reducing the transformer inrush content and use an Amperite 6NO60 delay relay on the 6.3 V winding to short the NTC's on the primary side. This has the advantage that you can use fuses that are marginally above the normal power consumption when the amplifier has warmed up increasing protection.
One could go even one step further and use a delay relay to switch the filament of a damper diode after all the other tubes have heated up. And to protect the damper diode you can use some NTC's in series with the B+.
Perhaps a better alternative to the Amperite is to use an adjustable Tempatron 2B relay that will drop out immediately when there is a power interuption switching the cooled down NTC's back into circuit. (but I try to avoid using solid state parts)
AM
sure, you can use NTC is series with the primary, and you can also use ntc in the secondary...no laws are violated when you do...
Hi, Generally good idea...however the 6NO60 is only rated for 200 volts. I use them all the time with them driving a relay that can handle the B+. Also use a capacitor and resistor in series across the B+ contacts to prevent arcing and burning. Values range from roughly about 0.1uf to 1uf and 47 to 220 ohms depending on the voltage present. The latest "formula" I saw said 0.5 to 1.0 uf /amp and 0.5 to 1.0 ohms per volt. A formula I saw was C=I*2/10 and R= V/10i(1+50/V) Or in English C in uf = I squared (amps) divided by10 and R (ohms) = Voltage divided by 10 times I (1+ 50 divided by V). Hope you are good at math. I just use the cheat "formula".
There is normally not a high voltage across the NTC's that you are shorting and then the voltage rating is not exceeded only 30VDC (found elsewhere) or 115VAC .
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One thing to keep in mind about Amperite bottles is that they close *very* slowly, and arc during the last part of closing. I've used them to short across fixed series resistors in the primary of filament transformers, about 100 Watts draw. They get replaced every coupla years, but I've got a lot.
Once (and only once) I slacked on maintenance, contacts failed, and B+ soared to around 2KV (choke input supply, no significant bleeding), on 660VAC motor run caps, for about 20 - 30 seconds. They're all still in service, but I'm a lot more watchful.
My take-away is: don't believe the 3A contact rating. That's after the contacts have closed.
All good fortune,
Chris
Once (and only once) I slacked on maintenance, contacts failed, and B+ soared to around 2KV (choke input supply, no significant bleeding), on 660VAC motor run caps, for about 20 - 30 seconds. They're all still in service, but I'm a lot more watchful.
My take-away is: don't believe the 3A contact rating. That's after the contacts have closed.
All good fortune,
Chris
Hi,
I’m using an Amperite delay too to switch a relay. One of the relay contacts keeps the power switched on while the Amperite heater is switched off by the same relay. So when I switch on the amplifier the Amperite will switch after 30 or 60 seconds. Doing so, the Amperite is in fact no longer needed and the heater is switched off.
If I switch the amplifier off and then back on again, the Amperite will have cooled and have the same delay again. So I never leave the Amperite heated!
Regards, Gerrit
I’m using an Amperite delay too to switch a relay. One of the relay contacts keeps the power switched on while the Amperite heater is switched off by the same relay. So when I switch on the amplifier the Amperite will switch after 30 or 60 seconds. Doing so, the Amperite is in fact no longer needed and the heater is switched off.
If I switch the amplifier off and then back on again, the Amperite will have cooled and have the same delay again. So I never leave the Amperite heated!
Regards, Gerrit
My reason for a standby switch is I use mesh rectifiers - AZ1 and AZ11. These can spark if they're not hot when the high voltage AC input is applied. There'a a few posts about what to do to avoid sparking, and this was one of the better suggestions.
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Although relay automation would be convenient I’m going simple as can with two switches, i.e. for fillament and B+, as needed to comply with the datasheet requirement to pre-heat a rectifier for use at high voltage for my 845. Found a neat circuit which guarantees heaters go first whichever switch gets flipped first.
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I've just started to re-read Tomer "Getting the most out of vacuum tubes" and will need to rethink my approach.
Basically on page 19 it mentions that all the filaments should heat up at the same time. Where this is not possible then those tubes that are required to supply the current should be reaching their operating temperature before those tubes that draw upon that supply.
I'm starting to lean towards only using a string of NTC's in series with the rectifiers until the filaments have all heated up and then switch them out of the circuit.
@ Chris Hornbeck: Yes I have noticed the slow closing but considered it not to be a big issue for me since I switch only a few volts AC at a couple of hundred mA across some NTC's. I am thinking about changing to using a Tempatron delay relay (fits in the octal socket).
Basically on page 19 it mentions that all the filaments should heat up at the same time. Where this is not possible then those tubes that are required to supply the current should be reaching their operating temperature before those tubes that draw upon that supply.
I'm starting to lean towards only using a string of NTC's in series with the rectifiers until the filaments have all heated up and then switch them out of the circuit.
@ Chris Hornbeck: Yes I have noticed the slow closing but considered it not to be a big issue for me since I switch only a few volts AC at a couple of hundred mA across some NTC's. I am thinking about changing to using a Tempatron delay relay (fits in the octal socket).
McIntosh semicon amplifiers of the 1970's used a (beefy) 3-pole speaker protection relay with the third pole shorting around a couple NTCs in the primary. These work fine to this day, and can be opened to clean their coin silver contacts. Half a century at full primary current, so, you'll likely be just fine.
All good fortune,
Chris
All good fortune,
Chris
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Yes, that is what I have been using on one of my amplifiers: a couple of NTC's in series with the primary that are switched out of the circuit with the Amperite to stop the filaments lighting up like a flashbulb.
Perhaps one should only use a few NTC's in series with the silicon rectifiers (as suggested by Epcos) in addtion to the NTC's in series with the primary and don't make it more complicated.
Perhaps one should only use a few NTC's in series with the silicon rectifiers (as suggested by Epcos) in addtion to the NTC's in series with the primary and don't make it more complicated.
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I'm experimenting with an entirely primary side solution that has no requirement for a low voltage supply, 555 timer, etc. Only three parts, 1 quality Omron (ice cube style) relay with 120v AC coil, 1 thermistor, and one of these "Delay on make" modules used in just about every residential HVAC system to keep people from short-cycling their compressors. Designing a board for this now, I was gonna add a DC Blocker to it as well.
The module below turns on the relay coil 30 seconds after you turn the amp on. That relay simply shorts out the thermistor. In the ensuing 30 seconds (after you turned it on) the whole amp came up slower through the thermistor. These modules are pretty rugged, in wide use winter and summer, rain and snow. I just don't like a real hot thermistor running all the time. shorting it out gives it time to cool somewhat if someone were to short cycle the power switch, as an already-hot thermistor is useless. And less heat overall in the chassis. Of course this doesn't address separating B+ timing, but it should make the Filaments, diodes and reservoirs happier, especially if using a toroid.
ICM103B - ICM Controls ICM103B - ICM103 Delay on Make Timer (1-1,023 Second Switch-Settable Delay)
The module below turns on the relay coil 30 seconds after you turn the amp on. That relay simply shorts out the thermistor. In the ensuing 30 seconds (after you turned it on) the whole amp came up slower through the thermistor. These modules are pretty rugged, in wide use winter and summer, rain and snow. I just don't like a real hot thermistor running all the time. shorting it out gives it time to cool somewhat if someone were to short cycle the power switch, as an already-hot thermistor is useless. And less heat overall in the chassis. Of course this doesn't address separating B+ timing, but it should make the Filaments, diodes and reservoirs happier, especially if using a toroid.
ICM103B - ICM Controls ICM103B - ICM103 Delay on Make Timer (1-1,023 Second Switch-Settable Delay)
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