Fender twin reverb reissue help please

[dansamp]

ok guys hope someone can help
I have a '65 Fender twin reverb reissue on my bench
it is making a very loud buzz sound when turned on
I tested the power tubes -ok
I tested the preamp tubes 1 bad (replaced)
plugged the tubes back in same sound
did a quick check for burned resistors (appear ok)
I pulled the PI tube same sound
I pulled the power tubes same sound
I checked the OT for continuity primary to secondary ok primary to primary ok

my question :
is there a known failure on these amps that would make a loud hum buzz sound ???
like I described

thanks

Dan...........

[butwhatif]

check the primary filter caps if u have a cap tester or if one has come loose or a lead broken--they can go bad- do u have a scope--you should see major ripple in the B+, or check the B+ (6l6 plate supply) with your meter in AC volt mode-you'll see several volts or more AC on top of the DCV if the caps are bad-

[dansamp]

ok no scope or cap meter
but I will check with volt meter

thanks

Dan

[rfgordon]

If the amp makes noise with no power tubes installed, then the OT is coupling ripple to the secondary. This happened in an amp I built, where an internal wire of the OT shorted to the body of the OT.

It it's not a short in the OT (and some shorts may actually have significant resistance and not show up on a meter--had a bad reverb tranny that would only short with HT applied), then it's got to be a filter issue. I'd say replace EVERTHING in the PS--caps and resistors.

Or, if you have any kind of spare OT lying around, tack it in and see what you get.

[dansamp]

OK,
butwhatif thank you, thank you, thank you,

learn something new every day
I set my volt meter to AC and checked my plates and found 80+ volts
checked the center tap of the OT and the same 80+ volts were there
checked the PS board and couldn't reach it so I flipped the amp over and the hum went away WTF !!!
then it came back
so I took my positive lead checked checked the first cap pf B+1 and sure enough it sparked!!
the lead coming out of the cap was broken right at the cap
tried to solder it back but it would not hold
I subbed another cap I had and the amp works

now I have to find a 200uf @ 300 volts cap


rfgordon
thanks for your input,
I did suspect a blow OT but then ruled it out by checking with an ohm meter from side to side

again thanks everyone

Dan.........