New hum problem (solved)

[mat]

ODS50nonhrm-build. Worked very nicely for about 2 weeks but suddenly started to give noise (also without any tubes in the amp) when firing the amp.

On the soundfile (http://media.putfile.com/nonhrmpowerfilterbug) first I switch the amp (standby off) on (0:00) and there is louder noise. B+ is normally 470-480V in my amp. The voltage starts to get higher and on about 150V the amp gives a pop/cracking sound (0:13) and the voltage jumps at 250V's and then it starts to drop and on 140V I put it on standby (0:31). There is constant hum on background when the amp is on.

The guitarsound gets trough while being weak and unpleasant sounding.

Is something eating too much current ?

Should I first try to change:

-Main filter caps (new Spraque 100uF 350V x 2), or their 220k bypass resistors
-V1-V3 caps (new FT 47uF 500V)
-D-lator filter caps (new 22uF 450V)
-Choke

-something else ?

Thanks,

[ampdoc1]

I suggest removing one stage of amplification at a time from your DC line. IE Your layout might be like:

STDY SWITCH - FILTER CAP(S)/B+1 - CHOKE - FILTERCAP(S)/B+2 - RESISTOR - FILTER CAP(S)/B+3, etc

BE SURE TO BLEED THE DC FROM ALL STAGES OF THE POWER SUPPLY BEFORE YOU UNHOOK OR REHOOK ANY COMPONENTS!!!!!

In this case, first disconnect the CHOKE from the B+1 and check your B+1 voltage. It should be higher than usual. If not, it's either those filter caps, or possibly a bad output transformer. If this is the problem area, disconnect the transformer to see if that restores the voltage.
If this stage is OK, reconnect the line, then disconnect the choke (it could have an internal short), and check your voltage there.
When you get to the point that your voltage drops, it will probably be a bad filter. Very little past the B+1 or B+2 points draws enough current to pull down the DC as you describe.

ampdoc

[mat]

ampdoc, big thanks to You ! I followed Your instructions and the problem appeared to be the Spraque Atom 100uF 350V cap(s). As soon as I putted in a pair of F&T 100uF 450V caps the voltages came back and the amp sounds just fabulous !
It was first time I used the Spraques. They were brand new and I soldered them in with care and focused not to over heat them. Might be one out of ten thousand but I think I'll stick with the F&T's.

Thanks again

[greiswig]

ampdoc, big thanks to You ! I followed Your instructions and the problem appeared to be the Spraque Atom 100uF 350V cap(s). As soon as I putted in a pair of F&T 100uF 450V caps the voltages came back and the amp sounds just fabulous !
It was first time I used the Spraques. They were brand new and I soldered them in with care and focused not to over heat them. Might be one out of ten thousand but I think I'll stick with the F&T's.

Thanks again

Interesting...I thought Spragues were generally better regarded than the F&T's. Nice thing about the F&T's is their relatively small size. Which Spragues did you use?

[mat]

Which Spragues did you use?

This is the text on side of the caps:

SPRAGUE ATOM
TVA 1620
100UF 350VDC
0651H571 +85C

The guy who sold me these has not seen or heard of a bad Spragues to date. I quess I was just unlucky to have a fault one.