Fender Bronco Amp - tremolo ticking sound

[Bushbaby]

I believe that the deluxe has an optical photo unit in the tremolo section but there isn't one in the Vibro Champ / Bronco. I am wondering if its an close lead with electrical leakage or that the ECC83 I put in has gone microphonic. I was told (I cant remember who?) that it didn't matter what make of valve was put in this section as it doesn't form part of the direct sound output. Is this correct?

Best regards