yes kedsinger, it is meant to be like that,learning process
Even the EE educated people have to learn the behavior of the given circuit on the practical lenght.
Theres no better education than making practical mistakes ,and learning about things you need to debug,focused.
(It's amazing to see experienced service man/tech who recognise faulty component from sound of amp,in 10 minutes the job is done.)ouch
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First thing I will do with a TMB is to apply shielded input wire/isolated input jacks,second I'll check ground buss/ground loops.
third i'll try to fix oscillaton with shopstick,and it fails i'll make sure that all wires are short,and not parallel to each other.
Tap the preamp tubes to find microphonic/oscillated one,put that tube in PI ,swap tubes ...
After that i'll swap OT primaries if it helps.
I'll check OT output jack ,this should be non isolated type.
I'll make sure that OT wires are not close to preamp wires/ stage.
Be sure that you dont have cold solders,check the underboard wires if you have ones.
Try not to modify amp till is running healthy,for me is important to notice and remember original sound and go from there...fine tunning.
It should be fun and learning process always,the amp which is running perfect from the beggining,will actually teach us nothing
Be carefull with high voltages and have fun.