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1) if possible, build a lamp bulb limiter (search it), you can make one even with an old desk lor night table lamp, using a 40W to 75W old type filament lamp, not a modern CFL , although you can use one of these: 
because they still have a filament inside.
Plug your amp there, the light should glow dull red or orange; if it shines with full intensity, the short is confirmed.
If not, just once use a 2A slow blow and try it for the last time; if it blows junk the transformer; if not, carefully measure secondary voltages.
I suggest you safely tape all extended wires to a piece of wood or tabletop so you can measure them without holding them in your hand.
2) if dead, start searching for a replacement, you'll roughly need an around 80VA transformer (larger is acceptable as long as it fits in the chassis cutout), with secondaries:
* 12 or 12.6 VAC @ 500mA
* 17+17VAC (18+18 is acceptable and somewhat easier to find) @ 1.5 or 2A
now this is a tough nut to crack:
* 200+200VAC (+/- 10/15%) @ 10mA or more.
3) if absolutely unavailable, you can use 2 transformers , but they won't fit the existing hole, to boot you'll probably find a toroid for the main one.
* 18+18VAC 1.5 to 2A
* 12VAC @ 1A
+
* 220VAC to 12VAC , 0.5A to 1A , which you will use reversed, fed from 12VAC, to get 220VAC NOT centertapped, so you will need to add 2 extra 1N4007 to complete a bridge rectifier and get roughly +300VDC for the tube HV supply
Check Mouser, Hammond and ??Antek??? or similar, which have lots of tasty toroidal transformers at very good prices.
because they still have a filament inside.Plug your amp there, the light should glow dull red or orange; if it shines with full intensity, the short is confirmed.
If not, just once use a 2A slow blow and try it for the last time; if it blows junk the transformer; if not, carefully measure secondary voltages.
I suggest you safely tape all extended wires to a piece of wood or tabletop so you can measure them without holding them in your hand.
2) if dead, start searching for a replacement, you'll roughly need an around 80VA transformer (larger is acceptable as long as it fits in the chassis cutout), with secondaries:
* 12 or 12.6 VAC @ 500mA
* 17+17VAC (18+18 is acceptable and somewhat easier to find) @ 1.5 or 2A
now this is a tough nut to crack:
* 200+200VAC (+/- 10/15%) @ 10mA or more.
3) if absolutely unavailable, you can use 2 transformers , but they won't fit the existing hole, to boot you'll probably find a toroid for the main one.
* 18+18VAC 1.5 to 2A
* 12VAC @ 1A
+
* 220VAC to 12VAC , 0.5A to 1A , which you will use reversed, fed from 12VAC, to get 220VAC NOT centertapped, so you will need to add 2 extra 1N4007 to complete a bridge rectifier and get roughly +300VDC for the tube HV supply
Check Mouser, Hammond and ??Antek??? or similar, which have lots of tasty toroidal transformers at very good prices.
), and with a not too large bulb , say 40 to 60W.
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