New DHT heater

[Guido Tent]

Originally posted by Pjotr
Quite right KYW,

IMHO it is more effective to keep mains and rectifier related noise away from the DH cathode by proper LC filtering. A simple LM317 or LM338 will do then as a voltage regulator and electronic low frequency filter.

Just my 2 cents

Hi

It is not only about filtering, it is about exposing the filaments to an external impedance.

Read the presentation for background info

regards

[ThorstenL]

Konnichiwa,

Originally posted by ultranalog
That is exactly the point that has been mystified in this story.
A first order is easily achieved with an L200. Myself, I'd go for a 1 Hz, 4th order turnover or something alike.

Well, lets look a simple theoretical circuit. We take an LM317 for simplicity, 390R/1K2 voltage set resistors for 5V and a 1,000uF coupling capacitor for the AC and a 1R sense resistor. We get a turnover of 0.5Hz and thus at 50Hz 100 times the sense resistor as Impedance (100R) and at 100Hz 200 times.

If we increase the Capacitor (and sense resistor) we can achieve quit high levels of impedance. Using standard values for a 300B Heater supply without wasting too much power we may with to use 4,700uF/16V as coupling capacitor and 2R2 as sense resistor and 1k/2k7 "set" resistors for the LM317 we get over 4KOhm impedance at 100Hz (theoretically at least) and around 4.75V DC, just ideal for a 300B.

In this design we are loosing around 3.3V in the 2R2 Resistor, which suggests a supply with a minimum of 10V prior to the whole shebang. Using a pair of 16V 4,700uF Capacitors with a little LC common mode filter (at least 2A rating) and a 9V winding plus schottky bridge we should have a nicely working supply, very low noise, high AC impedance and a 7.5 second timeconstant, giving a nicely slow start.

The resistor could be replaced with a choke, making the slope 2dn order, but it needs a pretty beefy choke, 4.7mH/2A might be usefull there as it will reduce the required voltage level and will increase a little in 100Hz impedance on the Resistor.

Anyway, some thought experiements on "electronic chokes", which would make a nice DHT supply using inexpensive off-shelf parts.

Sayonara

[Bas Horneman]

read the site, I put a lot of background info there !

I did Guido!

But I simply don't know/understand how your design differs from a simple voltage reg followed by a current reg?

I am not an EE. And I think that most of your potential clients for that board will fall into that category.

Telling these kind of people to read the datasheet won't help you endear your product to them. At least I don't think so.


It's the same for your oscillators. I don't want know necessarily why they are better...but I understand that 3 ps is better than 200 ps.

But I can't understand why your filament reg is better than the vr/cr type circuit. Because I don't even know the specs of a typical LM317 vr/cr....such as I plan on building for a friend/customer (Cleo V with Doede's VR/CR. )

Regards,
Bas

[ultranalog]

It is not only about filtering, it is about exposing the filaments to an external impedance.

Please, elaborate on the difference between a filter and a (frequency-dependent) impedance.

[Guido Tent]

Originally posted by Bas Horneman

I did Guido!

But I simply don't know/understand how your design differs from a simple voltage reg followed by a current reg?

Bas

Hi Bas,

A voltage source has a low impedance, compare with car battery, it maintains the output voltage, "regardless" of the load

A current source has a high output impedance, it maintains the output current, regardsless of the load.

My design has a high output impedance, hence does not short the differential audio current generated in the DHT

This to me is the main reason why it sounds better

And it does sound better, to many ears already

cheers

[Guido Tent]

Originally posted by ultranalog


Please, elaborate on the difference between a filter and a (frequency-dependent) impedance.

Remco,

My design filters as well, as does the traditional voltage regulator.

In addition, my design has a high output impedance, this contrary to a traditional voltage reg.

regards

[ultranalog]

A current source has a high output impedance, it maintains the output current, regardsless of the load.

Output current: automatically adapts to required level to reach voltage specified above

This doesn't compute.

[Guido Tent]

Originally posted by ultranalog




This doesn't compute.

If you look at the data at my site you will understand it computes

It maintains stable voltage for DC, and high output impedance for audio frequencies

[ultranalog]

The power is delivered by a voltage source. In other words, this circuit behaves like a choke.

And it's priced likewise...

[Guido Tent]

Originally posted by ultranalog
The power is delivered by a voltage source. In other words, this circuit behaves like a choke.

And it's priced likewise...

You're free to put a choke in your designs. It is actually where I started.

It''ll be chunky, as it needs to show quite some impedance quite early in the frequency domain, and it would be fine if it is 0 ohm DC, say thick wire and loads of iron, to achieve Henries and amps, otherwise you keep adjusting the whole thing during use and the voltage source in front needs to be stable and low drop due to heat requirements.

Yes, when you've done that, you're about there. Recalculate system solution price, dealermargins included, and put it in contrast with size, weight, performance and 5 years of warrantee.

cheers