Simplistic MosFET HV Shunt Regs

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A

AndrewT

R.I.P.
Joined 2004
Roll,
You don't need a shunt regulator.
Just a CCS rated for the current you want through the heaters.

Poty,
Why should the CCS vary? The temp variation is fairly low.

Poty,
with voltage drive the power dissipated in the heater varies as V² / R
If R varies the power varies inversely in direct proportion to the R
With current drive the power dissipated in the heater varies with I² * R
If R varies the power varies in direct proportion to the R

In either case a 1% variation in heater resistance leads to a 1% variation in dissipated power and a slight change in temperature for emission.
 
P

poty

Member
Joined 2011
RollE2k said:
Why would they be stressed? tubes doesn't need 6.3v exactly, they are often rated 5.7-6.9v or at least 6-6.6v, and they are pretty much never exactly the same.
So if i set them at constant current that gives 6.1 or 6.3v between different tubes - it doesn't matter.
And the heater is pretty much the same as a light bulb - and when does those often break? - exactly, when you turn them on.
Click to expand...
When you say "rated" - could you think that they are rated also for the inrush current? If you look some messages earlier - you'll find an real example of exceeding rated values while using the current powering.
AndrewT said:
Why should the CCS vary? The temp variation is fairly low.
Click to expand...
Could you please explain what it is about?
AndrewT said:
with voltage drive the power dissipated in the heater varies as V² / R
If R varies the power varies inversely in direct proportion to the R
With current drive the power dissipated in the heater varies with I² * R
If R varies the power varies in direct proportion to the R
In either case a 1% variation in heater resistance leads to a 1% variation in dissipated power and a slight change in temperature for emission.
Click to expand...
The question is about different thing. Please look some messages earlier.
 
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A

AndrewT

R.I.P.
Joined 2004
poty said:
............................ And you will have different voltage across the heaters because of different tolerance for heating resistance. Very good thing for different channels, balanced design, push-pull, SRPP...
Click to expand...
you raised the tolerance of the heater resistance
Aha, and tune every time the current changes!
Click to expand...
you raised the issue of time varying heater drive.
 
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poty

Member
Joined 2011
AndrewT said:
you raised the tolerance of the heater resistance
Click to expand...
AndrewT said:
you raised the issue of time varying heater drive.
Click to expand...
Both issues are about the same. Serially connected tubes with differences in working point current as much as 20% due to tolerances by design means 20% differences in voltages across them. Of course it is possible to tune current for each specific tube, building dedicated CCS, but what would be the advantage of such complications in design and more important - for sound? Salas has already done the experiment showing that in the stable state we have the same voltages and current in the heaters. There are no signal, different frequencies, even changes during the usage time (excluding the startup and shutdown times): why to use such complicated circuit with great bandwidth and unprecedented stability? If the main concern (not shared for me) is the inrush current - there are much simpler methods of achieving stepped or smoothly increased power, than CCS...
Once more: is it possible to move the discussion to a new thread to not contaminate the Salas'? It is contrproductive to continue here.
 
TonyTecson

TonyTecson

Member
Joined 2003
poty said:
It is not MY problem actually. If a person want to, Russian way to say, steps on a rake over and over again and not learn from that - it has all right to do this.
My main idea - the tube filament is designed, tested and specified by voltage, not current. Then - voltage supply is the best way of doing this without harm and danger. That is all. I can't continue to discuss it further here, because I don't want to make this thread one more dump place - about everything and not about anything.
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I was in Russia for six years as a QC Engineer, i can understand where you are coming from....

i am sure you are quite familiar with Mr., Thevenin and Mr. Norton, two ways to look at a circuit arriving at the same conclusions....

the thing with tube heaters is that it has a cold resistance many times over its hot resistance....

voltage source or current source? makes no difference to me....
in the end, it is the final terminal filament winding voltage that determines how much current a filament draws...

and for as long as that terminal voltage is within specified range, your tube is guarranteed by the maker to work....
 
K

king4joy

Member
Joined 2011
Personally, I seek and try difference methods of filament supplies....and tube loading methods (other than resistor loading...choke loading...).....is to try to have a more and more close to live musical performance from our Hi Fi system in our living room....

I do not mind if my tubes live shorter as long as the music is lively......

My reason to go DIY......
 
roger57

roger57

Member
Joined 2006
poty said:
I did not say that in such refined case it would not work. I think if you got some directly heated tubes or a bunch of several smaller or different-current tubes - you can easily reproduce the problem (I did it for 4x 12AX7 + 2xKT-88 with such problem).
According to your experiment: the current/voltage was stable in 30sec in first case and "almost instantly" in the second. The amount of energy passed was definitely much lesser in the first experiment for "about the same time" of lighting. It means that something was wrong in the experiment.
Click to expand...

In Morgan Jones Book, titled "Valve Amplifiers", he has at least one CCS heater circuit that he believes is superior to a voltage regulate type. Nothing wrong about that, coming from a guy like that! :D
 
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