"Bo-Lennart"

** Original condition is best for sale value.

About the tubes (it uses KT77 for the output-stage),

** The Quad 2 uses KT66s ( or 6L6GTs ) and these give the best results.

KT77s (or EL34s ) cannot be used unless extensive internal modifications
are in place to compensate for the different bias and gain of that tube.

Seems your Quad 2s are heavily modified.


Well, there is labelled on the chassie "KT77".


** So what - did you see who labelled it so ??



But , as You mentioned,
on all schematics I found on the net, they all show KT66.
I also found that the resistor R12 is at 150 ohm instead of the 180 ohm
that are stated everywhere.
But do You think that could be a modification to get the right bias
for that KT77?


** May well be the only mod done.


That's the only change that I can see concerning the original
schematics.

** OK.


Well, about the input modification. (transformer at the input). It
seems that it might have been done at the factory.


** Just as unlikely as the theorising that Quad did the KT77 mod.

Far more likely is that some tech at the TV station did it.


Do You think the Swedish Television ordered a custom-tailored
version???


** Go ask them.


OK.......let see if there is more reply's coming in.


** The substitution of KT77s for KT66s is no improvement to the Quad
- KT66s being the more linear tube in that amp. THD figures goes up by 4
times or more when EL34s are substituted, even with the bias adjusted.

Buy some good KT66s and put that cathode resistor back to 180ohms.

Then try them on eBay.



........ Phil