WTF-MULLARD 6CA7 in Mark IIB

[McBarry]

I'm having a little panic..
I've got Mullard 6CA7's in my 60w MkIIB..
They work OK, but I'm wanting to get some vintage Sylvania 6L6's in there.
Am I right in thinking it would have had to be modified to accept 6CA7's?
Certainly inside there looks to have been no work around the power tube area.
In fact only new part I can see is a reverb mod to give reverb control on lead channel, and a polyester green-cap around V4 where a Sprague orange drop would have been..
Am I right in thinking 6CA7 are not simply interchangeable with 6L6????

 

[McBarry]

Thought so.
So then, if prev owner was trying to use it as a simul-class like the MkIII with EL34 in outside pair (except this one has only 2 p/tubes, no 60/100sw or full/half sw, or a/ab sw), wouldn't he need to have changed the OT at least?
But also change the Bias circuit and add more plate voltage???

I'm going inside it today with meter, but it all looks like he's put in the 6CA7's with no mods, but got away with it...

 

[McBarry]

no plate volt check yet, but the P/T is X61 - 162318 = export 60w power tranny, yes??
OT is: T60 152019
I get 60w, but is the 152019 simul-class????

 

[McBarry]

Thx George, brilliant stuff.!
With no changed resistors in PSU or around the sockets, I'm reckoning more and more he's just put these Mullard 6CA7's in there, and has gotten away without destroying them of anything in the amp..

Any takers??

Because if it's so, it opens up a whole new realm of sound for these amps, given I'm reading the Mullard 6CA7 is kind of "mid-way" between an EL34 and 6L6..