G-PULTEC problems, please help!

65dB gain loss is wrong.

1) Using the filter alone, no amplification, should give you approximately 20-25dB loss when set to neutral - check this first. If loss is different, check for wrong order-of-magnitude resistors, pots - and for shorts. The whole filter can be checked with unit powered off completely.

2) The amplifier board should give you some 20-25dB of gain from input to xlr's. Check this. If wrong, look at cabling, pcb integrity, and connection (through a capacitor) to the grid of lower tube half.

Substitution of transformers is not always a great idea: we use 5402 as 1:1 for the output - your 4:1 will give you 12dB less than what we set out for.

+122V at output coupling capacitor shows that tube driver stage is setting right, and can be expected to be alright if it checks out in point 2).

Jakob E.

Tried to rewire trafos. Also tried multiple different combinations. Im close to giving up. Tbh i dont have time to figure shit out with these edcors. Ill eliminate them and use LL5402 only for output with unbalanced input.

Am i losing gain again if i build this with LL5402 output and unbalanced input?

darkus said:

Am i losing gain again if i build this with LL5402 output and unbalanced input?

Click to expand...

That should be unity within the raw-gain-tolerances of the tube used, so within 3dB or so

But I think the problem is more than this.

Jakob E.

Ok so my friend came over to troubleshoot these and after hours of testing the trafos alone and in circuit we found the problem.
I had misplaced a 2.2ohm resistor over the output pins 2&3 when there should be 2.2kOhm....LOL.

So much trouble for such a stupid mistake. They work perfectly now and sound stellar.

Pics:
https://db.tt/1a0o6Cco
https://db.tt/LSQYy8gl
https://db.tt/EA2V7rD4
https://db.tt/V96SO1XF

Don Audio custom power transformer, PCB Grinder inductors, filter caps are Don Audios Cap kit (selected wimas,styroflex,polys)
Edcor trafos (600:600 and 15k:600) and DIY-Racked case.

Even tho i had to wire everything (because of the 3U case) i think this is one of my cleanest builds so far.

gyraf said:

wrong order-of-magnitude resistors

Click to expand...

Hmm, 25Hz attenuate working, boost is full bandwidth... off come the knobs  :

Update:  all caps measure good from pad side except 1uF measured nada...reflow & presto  8)

sidenote knobs didn't need to come off.  Hooray!

Looking back on the schematic, it is clear now.  Still learning

Matched for stereo.

All controls detented.

Quite happy about the result, I have to say.

Gustav

I have just finished my build and it sounds as it should except for high boost and high Q. I've been through the thread and have confirmed that my in/outs to the amp are correct and my switch is working correctly. I've confirmed the correct wiring and correct operation of the high boost pot and the Q pot.

The thing is I'm actually getting some effect from the high boost but it's very subtle. So it seems like audio IS passing through the high boost section of the circuit but not functioning properly.

Could this be an inductor problem? i.e. the switch is engaging the caps in the high boost section but the inductor isn't functioning properly?

Solved it - had a 2k pot in the high boost section

anyone have the edcor xs 1100 wiring diagram for this pultec eq?

Hi guys.
I just finish a stereo g pultec.
I started by check 6.3v and 250v rail.

Its ok for 6.3v but i read 290v between  the 3k3 2w big resistor and 220uf cap.

So i try to replace the 3k3 by a 20k 10w and i read 275v.
I use Power Transformer - Pri.: 2x115v- Sec.: 220v, 9v and 5v from Don Audio

should i put a 40k to get my 250v ?
Thanks

i just try a 40k i read 300v between A1 and 220uf 350v cap.
Something goes wrong??

mrkrawn said:

i just try a 40k i read 300v between A1 and 220uf 350v cap.
Something goes wrong??

Click to expand...

What is A1?

You should measure the voltage after the drop resistor. It should remain relatively unchanged before the resistor.

If you suddenly dont see a drop, you should check if your LM317 overheated and shut down (No regulation means no heater voltage, which will result in a zero current draw on tubes, which means no drop over the high voltage drop resistor).

You haven't stated your location, so we dont know what mains you have.

Gustav

thanks gustav
A1 is pin 4 of tube socket ecc88.
I'm in 220v country.
I did my first test with no tube and no front panel
i just check voltage before put the ecc88
the 6.3v is ok my lm317 is not hot.
Is it normal with no tube to get 300v between  250v point pcb and 220uf350v negative leg?
Thanks

I hope we're talking of the same built here,I refer to Gustav's stereo kit now.The psu must have a load,so I started with the tubes inserted and a higher value drop resistor.
The tweaked it down.


Best,


Udo.

i have build 2 pcb from gyraf pultec rev4 not stereo version

mrkrawn said:

Is it normal with no tube to get 300v between  250v point pcb and 220uf350v negative leg?

Click to expand...

220VAC x square root of two (or about 1,4) will land you at about 310VDC, so thats nothing out of the ordinary.

Again, you will not see a drop with no tubes installed, simply because there is no current draw. (V = R x I, and with no tube installed, I = 0)

Gustav

Thanks gustav

i will try to take mesurement with the ecc88 put in the socket with a 20k 10w to start.
I read in this topic a guy  put a 18k another guy a 33k5.
So Whats the best for G pultec 250V 240V 225V ?
i think i will  test one channel with LM350 or LM338 to be sure.
I don't want to broke my 2 matched ecc88 which cost me a lot .

Thanks for your help guys

Best is probably some 210-225V with unit heated up.

Jakob E.

Thanks a lot Jakob