hum in high power tweed twin amp

[stringbender.dk]

I got a mail from the tech today.  he got a good and a bad news.
it's hard for me to explain in english, but he did a try on dc heaters. that didn't help.
then, I asked if he could rewire the ohm, so I can pull out the two output tubes, and get less power.   he noticed a reducing of the hum, when he did that   :)

he found some resistors that didn't matced the colour code in the diagram/layout.  he changed them with new ones.

And he extended the green leaders, so they now are soldered to the lamp, and then down to the tube, as on the layout.

and he has picked on the filter caps, but founded nothing. he have been trying many of all those good advise you guys have been giving, and some he found in books. 

I'm going to him on Friday, and I can't wait to hear the result.   If just the hum is half as much as before, I think I will be happy  :) 

[Leevi]

I propose a check of the negative bias voltage with oscilloscope.
If there is ripple visible the bias voltage should have a better filtering, maybe by adding an extra filtering stage there.


The check all the grounding points. Normally a ground bus wire is a good solution for preamp.


/Leevi

[stringbender.dk]

I got the twin amp friday. and saturday I tried fire it up.  I'm happy :)   it's still a bit noisy, but nothing compared to how it was before. and another bonus is that the tech wired the ohm to 4ohm, so I can pull two of the 6l6 out and only get the half power. So now I can fire it up some more than I could before.

thank you guys for all of youre advises!  now, I can't wait for the next gig :)