strange noise in my 66 blackface fender twin not re issue

[chris61]

hi again every one,
this recapped twin has been operating perfect for some months
but now
there is a strange distortion that follows every note
sounds kind of like a flange pedal with some oscillation
the the amp sounds super in the attack but the the sustain turns into some kind of alien sound
you can hear it real good as you back the guitar vol off
happens on both normal and reverb channels and no amount of poking or prodding seem to affect it
any thoughts any one?

[loudthud]

Most common cause of this type distortion is a bad first filter cap. Probably one of the two caps in series is bad or has become disconnected.

[chris61]

mmmmmmmm
these were a new set
got them at vintage amp south on ebay
get lemons some time i guess

[Enzo]

And just for science, play the amp chassis through a different set of speakers.

[pdf64]

A resistor may have drifted way off and made the amp prone to parasitic oscillation.
A bad connection, eg dry joint, loose tube socket female contact.
A bad tube.

[Amp Kat]

Record that sound and make a $million. Kidding, If those tubes are Sovtek WXT get them outta there. Could be several things but a bad cap or connection to one would be up there on my list.

[Kazooman]

mmmmmmmm
these were a new set
got them at vintage amp south on ebay
get lemons some time i guess

There have been lots of threads here and on other forums telling about bogus electrolytics. They have brand names and look perfect, but if you open up the can you can find all sort of junk inside. Often smaller value or voltage, cheap caps. The symptoms are often similar to what you described. The amp works fine for a while, but then goes south.

[riz]

Bad preamp or phase inverter tube, including loose or dirty sockets.

[chris61]

And just for science, play the amp chassis through a different set of speakers.

damn it was one or both of the speakers
I pluged it in to my mesa EVM cab and the sound cleaned right up

what do i know now?

[olddawg]

damn it was one or both of the speakers
I pluged it in to my mesa EVM cab and the sound cleaned right up

what do i know now?

Find a good re-coner.

[melvin]

Science, you win this time...

[chris61]

also
using an off board cabnet the reverb dosen't squeel win you turn it over 6
could that be the fault of a bad speaker
or just an issue with a combe cab?

[chris61]

happy new year to all
and thanks for your help!
this old twin always sounds better after coming here

[pdf64]

How is the reverb tank mounted? In a bag? Screwed down? Which way up?
Try taping thin card or other board over the open side, wrapping it in a thich towel, and letting it sit loose on the bottom of the cab, away from the baffle.