50 watter blowing mains fuse

novosibir · Post by **novosibir** » Sat Mar 03, 2007 8:33 am

Guitar Adjuster wrote:... but once you hit the strings it makes that horrible crackling sound. Power down, check all wiring, re-solder and touch up almost everything on the board including ground and the same thing happens????? Any ideas, photo's at the beginning of the post. I also switched out tubes including pre's and same thing.

Can you post a sound clip? Because there are so much different types of crackling!

Larry

novosibir · Post by **novosibir** » Sat Mar 03, 2007 8:45 am

In your 2-nd photo I think that I can see 3-4 lead dress evils:

- one of V3's plate wire (blue) is running very close to the violet FB wire
- the OT's secondaries are very close running to the 2-nd V3's grid wire (green)
- these secondaries are also very close to the 2-nd V3's plate wire

And - not seen, because below the board - maybe V3's common cathode wire (yello) is too close to V3's 1-st plate wire (blue), where they're crossing below the board?

These all are possibilities, where 'crosstalk' may occur at higher levels, which sometimes is heared as a 'crackling'!

Better run the OT's secondaries and also the FB wire between the output tube sockets to the selector switch!

Larry

Guitar Adjuster · Post by **Guitar Adjuster** » Sat Mar 03, 2007 2:46 pm

Larry,

I corrected all the lead "dress" issues, it still has not helped. No much volume when lightly playing then when you hit the strings harder the volume goes up with a loud crackling and distorted sound? Could it be one of the new TAD 50/50 cap cans? or the OT? I re-soldered almost every connection on the amp and still no luck.

Guitar Adjuster · Post by **Guitar Adjuster** » Sat Mar 03, 2007 5:29 pm

Well it's not the Cap Can as I subed in some new ones with the same results........I am thinking OT, how does one test the OT anyway?

novosibir · Post by **novosibir** » Sat Mar 03, 2007 5:44 pm

You'd need at least a test voltage of 1,500V, to do it 'right'!

Do you have a suddenly lost in loudness, when it starts crackling?
That indicates a bad/internal fryed OT!

Put a meter on your B+ and watch for a suddenly remarkable drop, when the crackling starts! If so, then the voltage on the primary flashes through the (burnt) insulation to the secondary, what means a dead OT!

Larry

Guitar Adjuster · Post by **Guitar Adjuster** » Sat Mar 03, 2007 5:46 pm

novosibir wrote:You'd need at least a test voltage of 1,500V, to do it 'right'!

Do you have a suddenly lost in loudness, when it starts crackling?
That indicates a bad/internal fryed OT!

Put a meter on your B+ and watch for a suddenly remarkable drop, when the crackling starts! If so, then the voltage on the primary flashes through the (burnt) insulation to the secondary, what means a dead OT!

Larry

Larry,

No loss of loudness when it starts crackling it gets louder when it crackles and then some nasty distortion. hard to believe that a brand new Mercury OT would be fried.

novosibir · Post by **novosibir** » Sat Mar 03, 2007 5:53 pm

Here we obviously do have the same dilemma:

http://forum.metroamp.com/viewtopic.php?p=102975#102975

Shure hard to believe, but possible, that a brand new OT is fryed.

Make the B+ test!

Larry

Guitar Adjuster · Post by **Guitar Adjuster** » Sat Mar 03, 2007 6:29 pm

Larry, at idle the B+ is 427 when I crank the volume to 6 on the high treble input and play the guitar the B+ goes down to 377 then as I stop playing it jumps back to 427. This is on my Fluke 87V meter.

Allen

novosibir · Post by **novosibir** » Sat Mar 03, 2007 7:40 pm

You do have 100

Guitar Adjuster · Post by **Guitar Adjuster** » Sat Mar 03, 2007 7:45 pm

[quote="novosibir"]You do have 100

novosibir · Post by **novosibir** » Sat Mar 03, 2007 8:25 pm

You might check it for leakage or temporarilary swap in other caps, of course step by step.

But a leaking cap, which causes bias shift with blocking distortion as the consequence occurs more with a farting sound instead of a crackling.

Larry