Heater voltage too low in Madamp G2

I just finished my Madamp G2 and it doesn't produce any sound.

I checked all the voltages and found that the heather voltage is too low. I
only measure about 3 volt AC against ground (it should be between 6.1 and
6,8 volt).

All other voltages are fine.

I have gone through the circut and cross checked with the schematic many
times and I can't see what I have done wrong.

Please give me a hint on where to look?

What can make the heater voltage drop?

When I take the tubes out, I still get 3 volts. Between the two blue wires
from the transformer I get 6,6 volt.

R14 and R15 are correct.


Kind thanks!
:confused:

Oh, then ALL voltages are correct

Thanks to you all,

The manual said something like (referring to the ground solder lug star): "This is where all voltages are measured against"...

So measuring between the heater pins (4 and 5) I am fine, reading 6,3.

In other words I do not have too low heater voltage and ALL voltages are correct according to the schematic.

And I still have a silent amp.

How do I check if I have blown the output transformer?

Thanks again!

Problem solved - plus new problem

Hey guys,


Thanks again for all your input.

Well, I have the amp playing now!

I had the output wires connected wrong to the output jack.

I fear that I shortened the OT by doing that, though.

Now, the amp plays, sounds a bit thin (like a transistor radio), and when I set the tone switch to "SMOOTH" it self oscilates!
I get a squealing self oscilating noise at high volumes. But only in smooth. "Normal" is decidedly thin and "FAT" sounds decent.

What causes the squealing, now?

The squeal comes from the speaker (an 8 ohm 10 watt Weber Chicago Vintage Series CVC8 8" unit).

Thanks again!


Anders

OK, thanks,

Can I post pictures here? Or can I send it to your email address?

I can shoot a picture tonight.

I have to say I changed the layout a bit, so the valve circuit is rotated 90 degrees clockwise and put to the back.
I needed to do so to make room for the speaker as I am doing the kit as 60's Fender style combo with the chassis hanging up side down.

This means that some of the wires take a different path and some ground wires is placed at more convenient places for the different layout.

Also I added a Fender style pilot light on the 6,3 volt AC in parallel to the heaters. Can that be causing the problem? It's not causing a voltage drop because it's in parallel.

Thanks a bunch!


Anders