keefaz

G-Pultec and bleeder resistor
« on: July 06, 2006, 04:05:47 PM »
Hello,

I am building the Gyraf Pultec and I am now in the voltage testing step.

It seems that the big capacitors need a lot of time to discharge themselves
(more than 3-4 hours) so I searched and found this thread :
Valve/Tube Safety & Bleeder resistors

I used a 3.2k 2 Watt resistor between the + and - legs of the second
220uf 350V cap (the one with the + connected to the pin 6, A1 of the E88CC tube)

Now, each time I power on the G-Pultec, the main fuze burns
(the fuze that is in the IEC connector, not the 4AT SRP PCB fuze)
This fuze is a 350mA fuze, it does not burn without the bleeder resistor

Maybe I should use a bleeder resistor with a bigger value,
what do you think ?

Regards,
Keefaz


gyraf

G-Pultec and bleeder resistor
« Reply #1 on: July 07, 2006, 03:36:11 AM »
3.2k 2 Watt is waaaay to low a value. 270Vdc. You do the math.

Better use a 220K or 470K Ohm 1W resistor.

Jakob E.
..note to self: don't let Harman run your company..

keefaz

G-Pultec and bleeder resistor
« Reply #2 on: July 07, 2006, 07:51:00 AM »
Thank you Jakob :)

I know the ohm law, like V = I R
but I didn't know it works for bleeder resistor as well.

Thanks again,
Keefaz

martthie_08

G-Pultec and bleeder resistor
« Reply #3 on: July 07, 2006, 03:42:57 PM »
uumm, maybe like this :roll:

P = U * I
U = R * I  <--> I = U / R
--> P = U^2 / R

U = 270 Volt
R = 3200 Ohm
--> P = 22,78 Watt

as Jakob suggests:
U = 270 Volt
R = 220000 Ohm
--> P = 0,33 Watt


EDIT: whoops, maybe I got this wrong, I misread and thought the resistor was blowing up...

keefaz

G-Pultec and bleeder resistor
« Reply #4 on: July 07, 2006, 07:54:03 PM »
That sounds logical to me, why that should be different :)

Maybe if there was not main fuze, the resistor would be blown indeed ?

Thanks for the math :)

keefaz

G-Pultec and bleeder resistor
« Reply #5 on: July 08, 2006, 12:17:17 PM »
mmmmh no luck...

After I put a 470k bleeder resistor, the fuse burnt again

I think that is because I use a fast blow fuse...
Maybe I should use a slow blow fuse for mains ?

Regards,
Keefaz

EKADEK

G-Pultec and bleeder resistor
« Reply #6 on: July 09, 2006, 03:15:11 AM »
maybe the fuse (in the iec connector) at 350 ma is just too small. try 1 amp or so and watch the unit power up or fail with your finger close to the mains power switch incase it all turns ugly. 1 amp shouldnt be so hi that the whole test bench goes up in a flaming mess .. so give it a go. put a meter on the hi rail voltage and heater supply rails and watch that they rise and stabilise quickly. if they dont .. then something is wrong with your build and you have to trace thru your circuit and find your mistake. work out some experiments and do da deducing.

peterc

G-Pultec and bleeder resistor
« Reply #7 on: July 09, 2006, 03:23:42 AM »
Are you using a toroidal transformer?

I've had issues with fuses blowing when used with a toroidal transformer. For valve circuits, I've found that I have to go with a 1A fuse, anything up to ,5A would blow because of the inrush current.

Peter
If opportunity doesn't knock, build a door.

keefaz

G-Pultec and bleeder resistor
« Reply #8 on: July 09, 2006, 05:44:24 AM »
Hi, thanks for the new ideas :)

The fuse does not burn with the ECC88 tube removed
out of its socket and without the bleeder resistor.

I measured 310Vcc for the high voltage rail and
6.3Vcc for the heater, without the tube in the socket.

If I put the tube in its socket or if I solder the bleeder
resistor, the main fuse burns.

I do use a toroidal transformer for mains, it is a 2 x 12V 50VA
(I did not find a 30VA)

I will try an 1A fuse, but what type of fuse should I use,
slow blow or fast blow ? (I would think I have to use
a slow blow one)

Thanks again

gyraf

G-Pultec and bleeder resistor
« Reply #9 on: July 09, 2006, 06:00:52 AM »
For toroid transformers of that size, you need slow fuses (type "T") - rated at 630mAT or 1AT - just to control the inrush current (magnetic start-up and initial charging of caps).

Jakob E.
..note to self: don't let Harman run your company..


EKADEK

G-Pultec and bleeder resistor
« Reply #10 on: July 09, 2006, 11:45:45 PM »
sounds like the ecc88 or its heater wiring on the socket is wrong. dont e88cc double triodes have different heater wiring from ecc88s?.
in short.. something about the way youve wired your heater circuit is shorting the heater circuit out and that would definitely blow a mains fuse. you can go no further which the amp until you make ammends to that fatal flaw. its one of the little wires mofo. {just checking tube data}
YES! the ecc88 and e88cc tubes both need 6.3v across pins 4 and 5. the heater circuit does not use pin 9 (as in ecc82 -83 etc). pin 9 is an internal screen( between the two triodes probably)

alk509

G-Pultec and bleeder resistor
« Reply #11 on: July 10, 2006, 02:16:16 AM »
Quote from: "EKADEK"
dont e88cc double triodes have different heater wiring from ecc88s?.


No.

In any event, I doubt it's the fuse, because it doesn't pop at turn-on with the tube and bleeder disconnected. And I don't think it's the tube, because the fuse pops even with the tube out, if the bleeder is connected (besides, the thing's on a PCB - there's no way to wire the heaters wrong).

:?

Peace,
Al.

Lest laziness get the best of you!

keefaz

G-Pultec and bleeder resistor
« Reply #12 on: July 26, 2006, 06:47:10 AM »
The GPultec works perfectly now :)

I used a 1A time delay fuse as advised and a 470k bleeder resistor.

Now I wonder why the 2.2K potentiometer (Labeled Hi Q on Jakob site)
doesn't do anything when I turn it...

Thank you all for your suggestions !

Regards,
Keefaz

peeceebee

G-Pultec and bleeder resistor
« Reply #13 on: July 26, 2006, 11:16:04 AM »
Quote from: "keefaz"

Now I wonder why the 2.2K potentiometer (Labeled Hi Q on Jakob site)
doesn't do anything when I turn it...


I thought the same with my unit- but put some white noise through it, crank a treble boost, and sweep the Q pot- The effect is a bit subtle without full-band content-


 

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