Zitat von: Pringles1 am Mai 13, 2020, 11:56
I have a question with the Bias Trimmer. The middle lug is welded on R 103 along with the side lug, is that correct?

Yep, thats right...

blues

Hi Jaime,

At pins 3, did you forget a "3" for the values? Or did you really measured 60V?

Laurent

Thanks Blues for your answer...

Yes Laurent, I measured again:
Signal: 0.06 V

V3:
P5: 21,6 V
P3: 65,9 V
P4: 3,0 V

V4
P5: 19,5V
P3: 66,6V
P4 5,3 V

All AC measurements and GND to chasis, is it OK?

Thanks,

Jaime

 :facepalm:
Should have read the posts before...
You measured the AC signal. now I got it.

I don't quite understand what you mean...
Have I already done something wrong? ... could you tell me how to make the measurements or where to find it?
Thank you very much, Laurent

I'm just building quickly the schematic on LT Spice following the schematic you posted above and I wonder whether you wired C8 correctly. The way your green lines are drawn, I could think, it's wrong. Can you check it?
C8 has no connection to R13 and R14. It goes straight to P3.

Thanks,

I check it and C8 does not have continuity with the resistances. In fact, he had protected one of the C8 terminals (blue sheath) to ensure that it did not any contact...

Hi Jaime,

This is what you should get at the input of the 6V6 with:
1- BELLS/BALLS at 12 o'clock and BLAST also (HALF). You should read about 11Vrms at pins 5 of the 6V6.
2- BLAST fully opened (FULL). Here you should read slightly over 30Vrms, even if the DMM will get wrong because you do not have a sine anymore.

Pics shows with a bias voltage of -34V. No idea what you have.

As you seem to get a low swing out of the PI, I assume that the PI wiring contains a mistake. You should try to get fresh air and then slowly and accurately check again all connections. Maybe you could start with new prints of the schematic/layout to make sure, you start with a new mind.

What value does the feedback resistor have (measured) ?

Laurent

ufffff :facepalm: :facepalm: :facepalm:

Thank you very much Laurent for your dedication, time and help. I have reviewed all the amp 5 times (yes... 5 :facepalm:), including 2 more during the assembly of each section and checking the value of each component with a transistor tester before placing each one ... I sure if I review again, in the same way, the result will be the same ... Probably the problem is my lack of knowledge...
Where could I get a fresh and easy vision on how to check the amp (I looked it up in the forum and I couldn't find it)
and Could you tell me about how I measure the value of the feedback resistor

Thanks,

Jaime

I calculated the bias as Robert told me a few days ago and adjusted it with the trimmer around 22-24mA.

The bias should be ok. I saw you have -33V at the beginning of the thread.
The feedback resistor is R23 on the schematic.

And don't be too rude with you. We all start from somewhere. Give you 1 day break with the amp.

I just see that you also measured the anodes of the 6V6.
There is something wrong. With 20V at the input, you get no swing for the output (only 60V).
How did you wire the output transformer? I think that the TT transformer has several taps on the primary. Which colours are wired where?

But Robert might have better recommendations regarding your measurements.

The R23 measurement: 14,64 KOhm

The TTOutput:
Blue and Brown wires solder to Pin 3.
White wire to B1.
Pink, orange, grey wires solders to 4,8,16 Ohms jacks speakers...
Black to GND chasis.

Everything seems ok.
There must be something but what