I'm with Stokes- go simple stuff without pulling chassis and get it to a reputable tech or MB if that's plausible..
Def love the FX loop check, and then check basic function to get RELIABLE symptoms and report these to tech.
Heater colour is vastly misleading as diff tubes have diff physical design and so heaters look different.
I/we can walk U through checking heater voltages but truly, I'd suspect it's a red herring, and I'd bet the shop checked anyway. Hopefully.
Even if the voltages are OK, current checking needs desoldering and is a bit involved.. not to mention dangerous..
Regarding diff brand tubes - matching for current draw should be poss, but things like gain, transconductance - I'd seriously doubt they matched these..
Leave 'em in, get it to a hospital.
It needs a laparotomy and then whatever shows up.
A new power cord... FFS.. how magnanimous of them...
Sorry not wot ur wanting to hear, but def the safest course of action.. Dave
