[Phil Allison[_3_]]

"Patrick Turneroid"


** More info:

In order to find the " open loop " THD of a Quad II output stage, I
removed the two EF86s and connected an output tranny primary to
the + supply and both plate pins.

The secondary was then driven by my bench oscillator, which has
very low THD - circa 0.002%.

This gave 52Vrms from grid to grid on the output valves - enough to
drive the stage to 10 W at 8 ohms and 1kHz.

Results: THD = 0.76%, DF = 1.

***This is all to be expected


** You bull****ting asshole !!

You had no idea what the THD figure was *open loop* !!!.


Also tried were Electro-Harmonix and GE 6L6GCs with closely similar
results, the EHs producing 0.8% and the GEs about 0.7%.

***Typical expected results.


** You bull****ting ASSHOLE !!

You had no idea what the THD figures for those tubes really were.

I only mentioned them to show the THD result was easily repeatable.


With EF86s restored to their sockets and the OP tranny removed, THD
dropped to 0.036% ( 10W, 8ohms) and DF improved to a respectable 10.

My conclusion is that the two EF86s reduce the THD of the output stage in
line with the level of NFB being used ( ie 26dB ) while adding virtually
*NONE* of their own.

***OK, I agree with your 26dB. I'd have to check my notebooks to see if I
ever measured 0.036% at 10Watts, but I cannot now recall ever seeing THD
that low.

** That would be because you LOATHE the Quad II so much you cannot bring
yourself to put in the effort to restore one to original specs and SEE how
well it works.

**** off and die you vile freak.



..... Phil