How to Measure Gyraf pultec EQP-1 voltages

Hey guys (and girls),

I'm building a dual gyraf pultec and am wondering how to measure the voltages. Since this is my first high voltage build and i'm fairly new to electronics i would like to ask for some advice. I already tried to use the unit using buggle boy ecc88 tube before measuring voltages. It did pass audio but the output was about 15 db louder than the input. The tubes i used now show a white powder like substance on the inside. I googled this and found that the tubes are probably broken. If they are i'm not sure.
So my question is fairly simple. At which points do I measure what voltages? Is there somebody that can give me a head start?

THANKS!!

Hi nadje,
you need to be very careful with high voltages!
The power pcb is still loaded with > 300v after you put out the power cable for a long time.

Before i put the power trafo to the pcb terminals i´d put the power cables into a normal terminal and measured the trafo ac voltages if everything is fine.
Just to prevent a defect or wrong power-trafo destroys your pcb parts. 220 to 250vac is fine for the high voltage. 9-15vac is fine for the ht voltage (measured on the terminal).

If the trafo is ok you can measure the high voltage most easy at the 3k3 2W resistor legs. The first leg should have around 350v rectivied and the second leg 250v.
The second point to measure is the outer leg on the 10u 25v cap or the outer leg of the 470R resistor between the cap and fuse holder.
You should get out 6,3v there. The minus pole of the measuring tool goes to ground.  

I can recommend JJ Tubes.

Only measure if you are wide awake and concentrated.

Be careful.

best
"who"

(..please use the dedicated help thread - http://www.groupdiy.com/index.php?topic=37837.0 )

The tubes i used now show a white powder like substance on the inside. I googled this and found that the tubes are probably broken.

Click to expand...

This indicates a mechanical error, i.e. the glass has broken and let air in. This is not generated by an electronic error, but probably by bending the tube pins a bit too much when inserting them into socket (the glass around the pins is somewhat fragile).

Having excess gain points towards an error in the filter board - verify that your filter board (with no power to the unit, not needed as it's a passive filter) attenuates your incoming signal by ca. 20dB - i.e. for 1V input signal there should be 100mV at the output of the filter board.

As for tubes, I've found that JAN6922-type tubes behave VERY well in this circuit, so does many of the NOS E88CC types.

Jakob E.

So i checked the tubes and they both have crack in the glass. I'll have to buy some new ones for those.
So according the way who described i checked the voltages of the toroid apart from the pcb. the voltages are 240 vac and 12.7 vac.
I hooked up the toroid to the pcb and put in my (broken) ecc88 tube. I measured 320v at the first 3k3 (i'm using a 4 w) resistor leg and 318v at the second. So that's nearly the same. Is it there a way to get the second voltage down?

yes, by using a working tube. it'll draw current thereby and reduce voltage. If still too high, use a higher value for the 3K3 - try e.g. 10K and 15K.

(..and please use the dedicated help thread - http://www.groupdiy.com/index.php?topic=37837.0 )