Tube with Power IC Output Stage - JLTi

[moamps]

Originally posted by JojoD818
This was the only solution I can think of.... inserting a cap between the pot and 3.9K resistor.

No way. Or, keep this cap (can be smaller value because tubes input impedance is high) and put additional resistor 1M from 3k9 to ground.

Regards

[carlmart]

Wow, 41 pages already on this thread!

BTW: where is Halojoy, that originally started it?


Carlos

[JojoD818]

Originally posted by moamps

Your measurements method is faulty.

Regards

I don't quite understand what you mean faulty. I have checked the DMM and it works fine.

Source is good, BTW, even if no source is connected, that weird things is still present without the small cap.

Is this what you mean?

[moamps]

Originally posted by JojoD818
I don't quite understand what you mean faulty. I have checked the DMM and it works fine.

Hi,
Measuring grid voltage without any bias (open) is faulty. Your DMM has very high DC input resistance and can't bias grid properly.

Is this what you mean?

Not really. Connect them between cap and 3k9 and ground.

Regards

[JojoD818]

Originally posted by moamps

Hi,
Measuring grid voltage without any bias (open) is faulty. Your DMM has very high DC input resistance and can't bias grid properly.

Not really. Connect them between cap and 3k9 and ground.

Regards

I will try that now. Just waiting for my soldering iron to get hot. Will get back to you in an hour.

Thanks!

[JojoD818]

I just did what you told me (put a 1M resistor) but I leave the 0.22 cap on. The tube output is fine now, only 0.4mV and does not react with the movement of my pot.

I hope there is an explanation for this. I have built this circuit many times, last problem was caused by too low heater voltage but I have checked everything in the circuit I do now, and everything is where they should be.

JojoD

[Ropie]

Originally posted by carlmart
Wow, 41 pages already on this thread!

BTW: where is Halojoy, that originally started it?


Carlos

Our friend Halojoy has been on permanent Hiatus (not his fault) for a while now. You can still catch him at ampchipdiy.com

[dioklecijan]

You can take 500k and result will be even beter.

[JojoD818]

Ironically, I have built Joe's circuit with no problems before without using any cap before the 3.9K resistor.

This leads me to my last question, would the cap (0.22uf) and resistor (500K-1M) interfere with the sound? I loved the sound of my former projects, I hope that cap and resistor wouldn't change the sound.

[JojoD818]

Hi,

I would like to ask what is the purpose of the 1M resistor and 0.1uf cap from the non-inverting pin to ground?

I have seen other IGC circuits but they just have the non-inverting pin connected directly to ground.

I also noticed that building the circuit without the tube (just the IGC) still produced a turn-on thump .

I have tried NIGC and they are dead quiet at on and off. How home the IGC has a turn-on thump?

JojoD