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mwl168

DIY mini T2 Build Thread

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3 hours ago, JoaMat said:


You don’t want to use same winding for small and output tubes. Separate windings for channels. So total four filament windings.

 

Thank you JoaMat, I thought seperate heater supplies was the case looking at how the heater pins are connected up via resistors to other parts of the circuit....

I think your are right about going seperate LV and HV transformers. I'm going golden reference HV and LV boards and have made a golden reference HV 220V dedicated board. I want to use synchronous rectifiers for the +-15V  on the golden reference LV board so I will go 2x15V  0.3A rather than centre tapped - Kevins sychchronous rectifiers dont like centre tapped transformers. Thank you for the specifications. Time to order some transformers....

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Regarding GRHV regulators. What’s the minimum voltage differential/headroom for the GRHV to work properly?

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5 hours ago, JoaMat said:

Regarding GRHV regulators. What’s the minimum voltage differential/headroom for the GRHV to work properly?

 

This reminded me of an exercise/experiment I went through with mypasswordis (we also consulted with Kerry) two years ago. I was hoping to figure out what's the highest, stable regulated voltage I can get from the GRHV with the Antek transformer I was using (300VA/325v rated).

The short answer is that it's very load-dependent. See the measured data I copied from my PMs with mypasswordis.  The GRHV was setup to deliver 426VDC rails when these measurements were taken. We never got to the bottom of this whole thing but I ultimately return my GRHV to regulate to 400VDC rails. 

Notice the pre-reg voltage is quite low when the power supply is loaded. This is the part that still confuses me.

Maybe mypasswordis, Kerry and others will chime in.  

 

 

 

                         secondary ac (Antek 300VA/325v)     pre-reg V at bleeder resistor        regulated output          current draw 

No load                         332v/332v                                       +461V/-461V                                 +426V/-426V            

HV Carbon                    326v/326v                                       +431V/-430V                                 +426V/-425V              97mA/101mA 

Blue Hawaii                  318v/316v                                       +422V/-414V                                 +416V/-408V              81mA/147mA

 

Edited by mwl168
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For me, with the golden reference hv connected to my modern blue hawaii via a variac the golden ref hv needs an *absolute* minimum of 315.5VAC at its AC input to regulate at 404.3VDC output.  In normal use I have 330VAC input to the golden ref for 404.3V output. 

 

Edited by jamesmking
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Am I the only one who uses 450Vdc output?

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Hi JoaMat,

You gave the power of the HV transformer (135VA or 143VA) what will be the power of the LV transformer?

Thanks

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84,3 VA. 

Voltage * current of each winding. Then add VA of all windings. Done. 

Reservation for errors!

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3 hours ago, mwl168 said:

 

This reminded me of an exercise/experiment I went through with mypasswordis (we also consulted with Kerry) two years ago. I was hoping to figure out what's the highest, stable regulated voltage I can get from the GRHV with the Antek transformer I was using (300VA/325v rated).

The short answer is that it's very load-dependent. See the measured data I copied from my PMs with mypasswordis.  The GRHV was setup to deliver 426VDC rails when these measurements were taken. We never got to the bottom of this whole thing but I ultimately return my GRHV to regulate to 400VDC rails. 

Notice the pre-reg voltage is quite low when the power supply is loaded. This is the part that still confuses me.

Maybe mypasswordis, Kerry and others will chime in.  

 

 

 

                         secondary ac (Antek 300VA/325v)     pre-reg V at bleeder resistor        regulated output                current draw 

No load                         332v/332v                                       +461V/-461V                                 +426V/-426V            

HV Carbon                    326v/326v                                       +431V/-430V                                 +426V/-425V                     97mA/101m 

Blue Hawaii                  318v/316v                                       +422V/-414V                                 +416V/-408V                     81mA/147mA

 

 

3 hours ago, jamesmking said:

For me, with the golden reference hv connected to my modern blue hawaii via a variac the golden ref hv needs an *absolute* minimum of 315.5VAC at its AC input to regulate at 404.3VDC output.  In normal use I have 330VAC input to the golden ref for 404.3V output. 

 

Thanks a lot, mwl168 and jamesmking.
 

Your information indicates – as I interpreter it - the voltage differential is in the region 30 – 40 volts. Good to know.

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1 hour ago, JoaMat said:

 Your information indicates – as I interpreter it - the voltage differential is in the region 30 – 40 volts. Good to know.

 JoaMat:

I want to be clear. In my case, a calculated rectified pre-reg voltage of 460VDC was not able to sustain the desired 425VDC regulated output with my GRHV when the load is more than 100mA per rail. For my Megatron build, I used a trafo with 350v secondaries to get regulated 425VDC rails from the GRHV under load. 

So, depending on the load, a calculated 30 - 40 VDC drop out voltage may or may not be enough with the GRHV.   

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On 1/11/2020 at 12:37 PM, JoaMat said:

Regarding GRHV regulators. What’s the minimum voltage differential/headroom for the GRHV to work properly?

I’ve been able to run the regulators with a 12-15v differential. Yes load can come into play. To be safe you should add another 10% on top of the desired HV plus the differential. That’s to accommodate voltage variations of the mains, which may not be applicable for you. 

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