• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6v6 PP - No sound

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hello

I'm stucked again. Building Poindexter's 6V6Gt push Pull amp.
Everything is finished, power supply seems to work, but no sound out from the amp.

Here is the schematic. I have 267 volt DC at the plate of 6v6 PP which is lower than the 315 volt specified. But 6v6gt specsheet specify 285 volt in push-pull triode configuration. Am i within specs?

Bias circuit seems OK, voltages are close.

5965 driver circuit is also low in voltage, 255 volts at point B instead of 295 volt specified, but the driver triodes seems to work, I measure signal at the 6V6 grid, approximately 10X higher voltage than the input. But still no sound.

Thanks for any help guys.
F
 

Attachments

  • bigamp1k.gif
    bigamp1k.gif
    11.1 KB · Views: 398
Administrator
Joined 2004
Paid Member
So that's about 26 mA per tube. A bit low. You should get some kind of noise out of it.

Turn it off and run your signal generator straight into teh output transformer and listen to the speaker. You should get something.

Don't forget to discharge the supplies first!

-Chris
 
If I put input signal on the input of the amp (0,3 volt approx), I get approximately 10 volt AC on the primary wires of the output transfo. So in theory, I should get some signal out I guess.

Output trans are hammond 1608. Here is the input schematic from manufacturer:

I connected the blue and brown to 6v6 plates, and red is 267 volt DC. The SG taps are not connected to anything right now.

F
 

Attachments

  • 1608 input.gif
    1608 input.gif
    3.9 KB · Views: 311
Administrator
Joined 2004
Paid Member
Hi Gary,
Your hookups are correct according to the Hammond catalog. You could ground, or not. There is no feedback to worry about. You should be getting something.

Do you have an oscilloscope handy? The circuit may be oscillating ultrasonically. I'd still expect some noise though.

Do me a favour and do the above test to make sure the output and speaker connections are okay.

-Chris
 
I can have an oscilloscope, but don't have it today. I will make the test later today or in teh next few days. Thanks for the info.

Also, the power supply caps discharge quite quickly when i put the power off. All the voltages are down to zero in maybe 10 seconds when tubes are in.

Is this normal?
F
 
Duh!

hehe
I found a big mistake. The output banana connectors were shorting with the frame. So no output of course....

I fixed that and the amp work well right now. Distorsion is present a medium volume, but I need to adjust supply voltages set bias correctly. Otherwise, sound is real nice!

I guess I needed to sleep on this one to find that stupid mistake... Thanks again for the help
F
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.