Depends entirely on current being drawn from the second tranny's secondary winding.

Yes,you are correct,but note that he already has an overheating problem.

I have seen "back to back" transformers used on many occasions,but unmatched windings are still a recipe for disaster.
There is no way of knowing what the current ratings of the low voltage windings are on his "junk box" transformers.

There is also the matter of the winding with 300v on it being run at above its voltage ratings.
Probably not a problem,but not to be encouraged.

The OP probably has a fair chance of picking up a secondhand transformer on eBay,with all the correct windings.

 

...
There is no way of knowing what the current ratings of the low voltage windings are on his "junk box" transformers.
...

That is the real problem...

 

If you have 240v RMS at the output of the reversed transformer,you should get around 337v dc out of a bridge rectifier (allowing for the voltage drop in the two series diodes on each half cycle).

If,however,you have 300v RMS out of the reversed transformer,you probably have different low voltage secondary voltages.
If the first transformer has a 15v winding & it is feeding a 12v winding,you will get the higher output from the reversed transformer.
This is a major "no-no",as you will be overloading both of the low voltage windings,so that one,or both will get hot.

hi ..thank you for your reply ..the secondary of the first transformer is 12v and it is connected to the 12 v winding of the secondary transformer ..i have put a 24vdc fan over the primary and it does a amazing job keep the transformer luke warm. thanks to all who shared their knowledge ..i am now planning on getting another el84 as a pushpull amp just to get some more output.cheers guys...Ta.

 

.....i am now planning on getting another el84 as a pushpull amp just to get some more output.cheers guys...Ta.

Well, that's garunteed to smoke the existing power transformers...

 

Well, that's garunteed to smoke the existing power transformers...

awwwww....better to leave it as it is then ..lol..