[Bradley Rush]

Just would like to know how anyone would have any Details about putting VARISTOR into a radio. Is there a way to put one so your filaments come up before everything else? I have not seen a schematic showing where they should be placed. ie before the fuse after the switch etc?

[morzh]

Varistor is not for that. Varistor (MOV) as well as Transorbs and such are there to absorb energy when input voltage spike of high energy source occurs at the feeding line.

If you want to delay a particular voltage there are other ways, though some are more difficult than others, but first of, why do you want to delay everything else?
In fact the filaments do come up first as for the high voltage to appear the recifier tube has to heat up first, and by that time teh filaments are up.

[Bradley Rush]

If I want to limit the voltage in to 115V and then limit the 6.3Vac have all the other voltages wait till the filaments are ready then go. What would be the best way?

I just thought with Varistors you might be able to this

[morzh]

No, you cannot do that. Not with varistors.

Again: what OTHER voltages? Are you talking of AC voltages? Why do you want to limit them?
There are only two AC voltages there and one of them is the filament, the other is the one to be rectified. And it is DOES NOT go anywhere before the tubes warm up so you in fact already have all other voltage lagging the 6.3Vac filament voltage.

Or am I missing something?

[Bradley Rush]

ok you protect with one 115v clamping voltage with a Varistors coming into the primary radio transformer. On the secondary 6.3Vac can you put another Varistors clamping voltage 6.3vac. Then another Varistors to the secondary windings supplying the radio. Because I have read that you would want filaments up first before the rest of the tube if it was possible. So is there away to do this with Varistors. Or you said you can do this with out them and only use the Varistors for protection the 115v into the main windings.

1. Is it important to have the filaments on before the rest of the tube.
A. What is the best way to make this happen?
2. Varistors used with a 115vac clamping to protect before the main windings
A. are there rules I should follow before the fuse next to the switch only so far from the transformer etc?
B. What would be the best Varistors to use?
3. a zeiner (6.3vac 12.6) for the filaments so they never go above.

[morzh]

Bradley,

I am sorry to ask you that but are you reading what I am posting?

[Bradley Rush]

Yes I was answering your last post. Trying to text it a lil better.

I get that the tube will not conduct til filaments are good and going.

So our saying the Varistors just protect and dont limit.

It is possible where i am at that someone could plug one of my radio's into a 220vac outlet

So if there was a way to use Varistors to make my RADIO beter too wanted to kill two birds with one ohm

[morzh]

Bradley

I will repeat:

1. the filaments will come up first ANYWAY. You do not need to sequence them.
Because for the high voltage to appear across the tubes first the rectifier tube needs to start conducting. And it is a tube, so it will wait for its filament to heat up before it conducts. So even if there is some short period of high voltage appearing across the rest of the tubes before they are fully heated, due to some differences in heating timing between the rectifier and the rest of them, it will be extremely short.
The whole idea is that the rectifier tube is a tube and as such behaves the same way the other tubes do, so whereas the heaters' voltage appears immediately on all the tubes (transformer acts instantly) the high voltage only appear AFTER the rectifier tube is warm and this is about THE SAME TIME when all other tubes are warm.


2. MOV (Metal oxide varistor) is NOT design to be used as a voltage limiter on a regular basis - its life is limited and then it fails, and it is not guaranteed that it fails open. You can use a transorb (a semiconductor device), but again - it will limit it PERMANENTLY. It will not delay anything.

3. If you simply want to limit the voltage from surges, then an MOV usually preceded by a fuse.

4. You can use an NTC thermistor to limit inrush if you want.
5. All this in tube radios is absolutely unnecessary.

6. Last. There are portable tube radios where the filaments are serialized and then a capacitor is used toi smooth the various groups of filaments. This is where a Zener is highly recommended in case of a blown tube so the rest does not blow. Such as in portable Zenith 6G001 and such.

[morzh]

Addition:

A simplest way of timing voltages is using a small semiconductor rectifier, RC circuits and electromechanical relays or simistors. This way you can create an exact timing of what you want. Again, it is a whole lot of trouble for a result that is not very useful.

As for the voltage limiting, MOV will protect you from a surge, but they are not used for a very tight voltage limiting: what they do is limit the voltage to a safety acceptable level of the equipment behind it, such as 220V may be limited to, say, 600V as it is a short surge and the elements after it will likely withstand it.

Now if you want to address a serious lasting voltage deviations (not surges) in your MAINs, like in India where what they call 220V can be 340V (and I am dealing with a project addressing exactly that right now designing a power supply for that region) then for old tube equipment in the olden times we used ferroresonant stabilizers which I think could still be found. They limit the voltage deviation quite well

[Bradley Rush]

Thx

Having not done this very long I thought I was missing something with the Varistors very easy to do that would help my RADIO's. I have now looked at the FERRORESONANT STABILIZERS very interesting. Looks like that will help me with any issue's of power surge or loss.