Drip 670 v3 HV Heater problem

[Pusch3l]

The PSU of this unit drives me totally nuts...
in the HV Heater section of the PSU is a 5W 0.1R resistor in the groundplane:
It is in the "JMP/.1" area right next to the Schottky Diodes



That resistor starts smelling after about 20 seconds when all tubes come to life at full voltage.
i installed the following tubes:
-TAD GZ34
-RCA 5651A
-TAD EL34-STR
-Valvo E80F

The RCA and Valvo tubes are NOS and tested more than 100% on a Funke W19
i did test with a siemens E80F and another RCA 5651 (without A prefix) and the behavior is the same

Without tubes the Heater Voltage (DC) is set to 6.3V with a Variac




and the voltage drops to about 5.8V when the psu is is installed and tubes are in place.

I have absolutely no idea left where to look for an error and if the voltage drop is normal.

 

[moamps]

IMO, it is a resistor between two filter stages and the current thru it is about 4A. So the power on it is about I2 R= 1W.
It can be shorted just because you obviously have a not enough voltage for proper work of LDR (cause of output voltage drop when loaded). What a crazy project, expensive 1% resistor in a heater power supply, fans on rectifier diodes, etc.  Good luck. You will need it.

 

[Pusch3l]

Crazy? It's a bit more like insane..
You mean the CMF55 in the power supply? Yeah that wasn't really planned but they're there now...
But you should see the 600R T-Pads 

If I get you right the voltage drop IS my problem. I can adjust the heater voltage so that wouldn't be a problem. But not the voltage drop...

Please excuse the question but could you explain what LDR means?

Greets

 

[Khron]

Please excuse the question but could you explain what LDR means?

I could be wrong, but that's more often abbreviated as "LDO regulator".
https://en.wikipedia.org/wiki/Low-dropout_regulator

 

[moamps]

LDR means low dropout regulator, the correct abbreviation is LDO, sorry.
For 4A at 6.3V stabilized with parts you have, IMO you need  minimum 8VAC perfect sine 50 Hz at the input.  Btw, I don't get it why the heaters for tubes in HV regulator should be supplied with DC stabilized voltage.

P.S. On the second look I see that the rectifier tube is heated from AC, so the load from stabilized output is lower, about 2A, so there is a bit lower AC voltage needed at the input.

 

[Rob Flinn]

I could be wrong but I think because it says JMP/.1 the JMP part stands for jumper & you can have either the resistor or a jumper.  I seem to remember reading about this on my V2 build.     

 

[Pusch3l]

According to the Sowter Datasheet from the 0526 Mains Transformer the Heater winding pumps out 6.3VAC/5A.

 

[Pusch3l]

I could be wrong but I think because it says JMP/.1 the JMP part stands for jumper & you can have either the resistor or a jumper.  I seem to remember reading about this on my V2 build.   

Yeah I tried the Jumper which ended up in a burned trace on the GND of the LDO and a rebuild of the HV Heater section..
You have a green PSU right? That one differs totally from the PSU.2 I got with the V3

 

[moamps]

Do you have a schematic for this PS?

 

[Pusch3l]

Do you have a schematic for this PS?

I am sorry to say no there isn't any.
the only documentation about this PSU is a video that can be found here:

https://vimeo.com/229433344

 

[moamps]

Then you should remove the resistor and find out using a DMM where traces from it go. Does this PS work if there is no jumper or resistor installed?

 

[Pusch3l]

Looking at some photos that I took during the rebuild I say the ground plane from the HV Heater is separated from the other ground plane. Only the resistor/jumper makes connection.

The orange line is the ground. The red line is just to clarify that the ground ends there

Greets

 

[moamps]

Where other pin of the jumper/resistor goes?
Btw, IMHO, very poorly designed  PCB. One 10mF capacitor at input of the LDO and 3  pcs of 10mF at output.

 

[Pusch3l]

The other side of the resistor goes to the connector that goes to star ground and on that trace is also a hole for the pcb-standoff.

 

[moamps]

Is green wire from this secodary  winding connected somewhere?

 

[Pusch3l]

Is green wire from this secodary  winding connected somewhere?

Yes, the green wire goes to the star ground too.

 

[moamps]

That's the cause of the problem with jumper/resistor. There is two way to reference  this PS to GND, with green wire OR with  jumper/resistor. If both are present, thru jumper/resistor goes high current from half part of this secondary. 

 

[Pusch3l]

And I already got goosebumps as I red your last post and thought about knocking my head onto the table  :
I will disconnect the green wire tomorrow in the morning and check back to you. Hope that solves my problem  ;D

 

[moamps]

I will suggest the mod here which will help for better regulation. It translates two elcos from the output to the input. To do that, you should cut the trace on two places (red) and use two thick isolated wire (blue and  grey).

 

[Rob Flinn]

Yeah I tried the Jumper which ended up in a burned trace on the GND of the LDO and a rebuild of the HV Heater section..
You have a green PSU right? That one differs totally from the PSU.2 I got with the V3

Sorry I can't check this at the moment because I am away working and won't be anywhere near my workshop until next weekend.