Added the dumbleator, fired it up and... hardly any sound...

[Joost]

Can you please help me? I added the built in Dumbleator. I also added the 1R bias current resistors. Finally, I upgraded the power rail resistors from 2W metal films to 3W metal films.

I checked and rechecked my wiring and started it up with a bulb limiter. Everything normal. Then I added tubes and did a full startup. All the voltages check out:

V1 pin 1: 188 V
V1 pin 6: 187 V

V2 pin 1: 197 V
V2 pin 6: 197 V

Dumbleator B+6 and B+7 are 360V and 260V which is good

V4 pin 1: 287 V
V4 pin 6: 287 V

B+ on screen grid of the power tubes is 439 V

I set the bias current for 36 milliamps.


I DO HAVE SOUND, BUT IT'S REALLY FAINT AND I HAVE TO TURN EVERY VOLUME KNOW UP TO GET A LITTLE MORE THAN BEDROOM VOLUME. THE SOUND IS THIN BUT NOT DISTORTED ON THE CLEAN CHANNEL

So what do I do?

I changed all tubes.... nothing.
I checked the wiring and it checks out.
I do get sound and all the voltages check out.

So what now? The amp was working perfectly before the tweaks.

Thanks so much for your help

[Deric]

Is this with nothing plugged into the 'Lator? If so, try plugging a cable directly from the send to the return. Any better?

If not I would start by triple checking the send/return jack wiring. Then triple checking component values - especially resistors.

Good luck!!!!

[Joost]

YEAH!! plugging in a cable straight from the send to the return is MUCH better!
thanks! What happened? it's supposed to work without that!

See attached schematic

Is this with nothing plugged into the 'Lator? If so, try plugging a cable directly from the send to the return. Any better?

If not I would start by triple checking the send/return jack wiring. Then triple checking component values - especially resistors.

Good luck!!!!

[Zippy]

YEAH!! plugging in a cable straight from the send to the return is MUCH better!
thanks! What happened? it's supposed to work without that!

Check which contacts of your jacks go to ground.

[Guitarman18]

If you are using Switchcraft switching jack sockets, check that the leaves are making proper contact (continuity) when nothing is plugged in. I use very fine sand paper to clean the contacts.

Cheers,

Paul.

[stelligan]

If you are using Switchcraft switching jack sockets, check that the leaves are making proper contact (continuity) when nothing is plugged in. I use very fine sand paper to clean the contacts.

Cheers,

Paul.

What he said. Switchcraft switching jacks can be faulty at times...

[jelle]

Yes, clean them, I use a piece of paper soaked in contact spray for potmeters that I work between the contacts, then retighten the contacts of the switchcraft.

Same goes for the other switching jacks in the amp, of course.

Jelle

[Joost]

thanks guys!

[Joost]

BTW, a very late update. It was indeed a faulty Switchcraft jack. Changed them both (send and return jacks) and turned out the last of the two was shot. Works perfectly now.