G-PULTEC problems, please help!

[Harpo]

...but the pcb layout is differing from schematic and has the throw connections just the other way round, IE you'd have to join 2 with 3, 5 with 6, 7 with 8 and 10 with 11, else you'd be partly shorting out an inductor winding section. As this mixup in your case only would give a different frequency response, the error must be in a different spot. Something like a broken pcb trace, a broken, wrong connected or wrong value Hi-boost Q pot, ...
good luck

 

[weiss]

hm i would be happy if i got a changing frequency response at all. i already replaced the q pot and high boost and cut potentiometers. no change.

 

[weiss]

found the problem after reading this post......

Problem solved!

I found out while remeasuring everything, that the 1M resistor above the bypass switch was giving me 1M at both positions of the bypass switch while that should have been bypassed.

So it was a bad connection in the bypass switch after all, but i didn't think of that before because the lo freq circuit was bypassed all right by that same switch!

!

i somehow... didn't wire the bypass switch  :

 

[gyraf]

..added filter function description to my post on the first page..

Jakob E.

 

[snaper]

Hi Guys,

Finally, I decided to go with the tube stage.
Right now, I'm using it with a custom, opamp based gain stage, but it is way to "clear".
I've ordered the missing parts and I'll etch the PCB next week, till that, I have two silly questions :

- I'd like to go with a transformerless version, I don't need them. Can I then omit the 2,2k resistors and can I route the signal with a jumper cable, like in the attached picture?

- I've ordered the custom GPultec power transformer from Don-Audio, is my connection correct?

 

[snaper]

Could somebody? I've may posted this to the wrong thread?

 

[iprovlek]

Snaper your connect with power transformer is ok!

You can omit 2k2 and take point from 4u7 cap and pin from GND to your output transformer!!!

 

[iprovlek]

From Don Audio site...

 

[iprovlek]

...

 

[snaper]

Thanks!
Go Croatia! (Greetings from Hungary!)

 

[iprovlek]

No problems Snaper....enjoy in your Pultec!

Im doing right now mine to and get power trannie from Don....

 

[snaper]

So, finally, got the 4u7 cap, so I was able to finish this build.
So far so good, no smoke, but, then, I've placed the tube in.
Right after I turn it on, the fuse on the board blows...
Power LED works, without the tube, the circuit seems OK, so short as far as I can see.

Any ideas?

 

[snaper]

So, finally, got the 4u7 cap, so I was able to finish this build.
So far so good, no smoke, but, then, I've placed the tube in.
Right after I turn it on, the fuse on the board blows...
Power LED works, without the tube, the circuit seems OK, so short as far as I can see.

Any ideas?

In the meantime I've measured the noval tube socket, I've got the heater voltage, ~6,1V and got ~330V on a different pin.
Are these OK?

 

[gyraf]

The fuse is between the two transformers - what value and type is it? Perhaps try with slightly higher current rating?

What tube do you use, do you have another to try?

ps:it's not good to run this for prolonged time without tubes, as you see the voltages gets really high on no-load. also make sure to have a way to test-for and discharge high-voltage before touching (!) - without a tube there can probably be high voltages for a loooong time

/Jakob E.

 

[snaper]

The fuse is between the two transformers - what value and type is it? Perhaps try with slightly higher current rating?

What tube do you use, do you have another to try?

ps:it's not good to run this for prolonged time without tubes, as you see the voltages gets really high on no-load. also make sure to have a way to test-for and discharge high-voltage before touching (!) - without a tube there can probably be high voltages for a loooong time

/Jakob E.

Dear Jakob,

Sure, thanks, saftey first!
The fuse between the transformers is a glass type 250V, 0,5mA one, I think it is a slow one, but I've checked, I have the very same fuse in the IEC socket as well.

The tube is a brand new "JJ E88CC Tube, Double Triode, Noval", from Don-Audio, I have only this, can't test with a different one, unfortunately.

Thanks for the info, luckly, I've run the tests only for a few seconds.

 

[gyraf]

Fuse wrong.

You need a slow-acting fuse of 0.5 to 1A - often named e.g. 1AT (T being for träge=slow)

If you used a 0.5A fuse and it was blown, check if it was a slow type - this is important as start current can be high

maybe try with a 1A

Jakob E.

 

[snaper]

Fuse wrong.

You need a slow-acting fuse of 0.5 to 1A - often named e.g. 1AT (T being for träge=slow)

If you used a 0.5A fuse and it was blown, check if it was a slow type - this is important as start current can be high

maybe try with a 1A

Jakob E.

You're right Jakob, it was the fuse!
I've replaced it with a 1A, works like a charm and most importantly, sound amazing!
Waaay better than with my +20dB IC gain stage!

 

[lars on]

Hi there !

Just finishing mine and doing some analysis.
What do you think of that curve ?
It's just the noise of electronics.

Trafo is out of the box.

 

[lars on]

And like rooster21 in the reply #302 I made this measurements for the LOW band.
Before to read Jacob's answer I found it strange me too.

What do you think about it ?
I think that the 6th curve is not correct. It's almost attenuation instead of little boost at 20Hz.

 

[lars on]

And generally I think that the frequency response is not low enough.
You see the low cut beginning at 200Hz ?

Not normal, isn't it ?