Golborne Vintage Radio - uTracer3 external PSU

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Drive isn't an issue per-se, it's getting a perfect copy of the pulse width after the opto-coupler.

So, I'm looking at a better opto=coupler than the ILD74 (which is about 3uS rise time) and maybe a pnp Schmitt trigger off 12 V to15 V supply to get a nice sharp pulse that is same duty cycle as original. Meanwhile I have isolated external 0.7 V, 1.4 V 2.1V, as well as isolated adjustable bench 30V and bench 120V PSUs. It's much better than before on internal for 4V to 18V with the IRF510 instead of the original overkill low resistance IRF1401Z part. The idea of an opto-isolated driver is so to automatically vary a fixed external PSU that has + out connected to H+, which is really internal PSU +19V and the Cathode voltage! The GUI has an option for an external PSU, but the original idea of that was that H+ was isolated from onboard PSU and cathode, so that scheme didn't work for direct filamentary cathodes, only insulated heaters. There is even an indirect valves with heater to cathode to save a pin on a B7G base.

My scheme will allow cathode and H+ to be connected anf to PSU+, and the floating FET switch to PSU -ve.

(28-06-2024, 10:24 AM)Mike Watterson Wrote: [ -> ]See this also about heater control: http://tronola.com/html/tube_analyzer_yo...page1.html
I'm not doing that.

The IRF510 does work very well instead of the IRF1404Z, but that is only for the internal supply. However the pulse width and thus the voltage seems wrong. With 19V PSU and setting of Vh = 9.5V it should look like 50% and it's much less. I'll try a different tracer.exe as there are many available and the Cal file / settings look correct.

There is also an alternate 3rd party GUI I've never tried.

I do now have a massive toggle switch for a fixed level external PSU rather than separate 2mm patch cables direct from valve base patch to PSU.

Apart from the free replacement GUI (which, IMHO, is FAR better than Ronald's), Nick Barton also does replacement firmware:

Replacement uTracer 3/3+ Firmware

Yes, it looks interesting. I'll likely look at that once I get my idea for controlled external PSU compatible with direct filamentary cathode working, or give up, or if the old workshop XP dies (I've 3 Linux boxes there) as his version has a real Linux option.

The real reasons that the uTracer needs a minimum of an isolated fixed external supply at lower voltage isn't the current or the inductions:
1: The effective DC or sinewave voltage is Sqrt ( Vs x Va)
where Vs is the recycled laptop PSU (18 to 20V, mine is 19.1)

A table (slightly messed up.
1st column is the effective DC (or sinewave AC) set in the GUI
2nd Column is the measured average voltage for different supplies, the 19.1 internal is 1st.

Code:
PWM supply without a filter                            

Vsup    19.1    3.0    5.0    12    30    60    120

Veff    Vav    Vav    Vav    Vav    Vav    Vav    Vav

0.7    0.03    0.16    0.10    0.04    0.02    0.01    0.00

1.4    0.10    0.65    0.39    0.16    0.07    0.03    0.02

2.1    0.23    1.47    0.88    0.37    0.15    0.07    0.04

4.0    0.84    3.00    3.20    1.33    0.53    0.27    0.13

5.0    1.31    3.00    5.00    2.08    0.83    0.42    0.21

6.3    2.08    3.00    5.00    3.31    1.32    0.66    0.33

12.6    8.31    3.00    5.00    12.0    5.29    2.65    1.32

15    11.8    3.00    5.00    12.0    7.50    3.75    1.88

(The 11.8 is really 11.78, but fudged for table)
Realistically about 4V is minimum usable at 19V supply, thus about 5V is maximum supply for 1V effective.
Thus minimums are:

Code:
19.1    3.00    5    12    30    60     120

4.0    0.63    1.05    2.51    6.28    12.57 25.13

Top row is supply.

Assuming the floating FET switch for an external supply working.

You'd need a big choke for filtered PWM, but then you'd still be limited by PWM resolution, however 1.4V might then be a minimum.

So really to see effect of heater voltage variation you need an external supply just about 10% to 15% more than rated filament/heater. Getting it to work with a floating FET switch and an external adjustable bench PSU will be nice.

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