Advise on how to bias KT66 on Marantz 8b

[l***@yahoo.com]

Some Marantz 8B enthusiasts recommend using KT66 and not EL34 for the
best sound using the same EL34 bias. I have tried to put some Chinese
KT66 on my 8b. Even setting the bias at minimum level, the pointer of
8b bias meter is still moved beyond the bias mark (about 1/3 between
the bias mark and the dot). The sound however is creamy and smooth and
all 4 KT66 are looked fine (tubes did not glow red).
My questions are:-

1) whether it is safe to use KT66 on M8b but how to set the bias
properly using the 8b's meter.

2) whether using KT66 would damage the 8b in long run (i.e. would KT66
put extra strain to my 8b?).

Please advise and thanks.

[chenchen]

I try KT66 on my Marantz 8 before (not 8B) and it bias fine, however I
use GEC KT66.
sound-wise, it really depends on your speaker, music, and the rest of
your setup, although KT66 sounds smoother than Mullard EL34, KT66 does
not sound as silky and dynamic as EL34 (on Marantz).

In my opinion, Marantz 8/8B should go with Mullard xf2 or better EL34,
experiment with KT66 is fine but for long term I doubt it's a good idea,
unless, of course, if the KT66 compensate your setup in a good way.

regarding safty, if your KT66 can bias properly then it's ok, if the
Chinese KT66 run away can cause high current in bias it could
potentially damage the output transformer. Really it's a little risky
to try Chinese tubes on your precious 8B.

Chenchen

Post by l***@yahoo.com
Some Marantz 8B enthusiasts recommend using KT66 and not EL34 for the
best sound using the same EL34 bias. I have tried to put some Chinese
KT66 on my 8b. Even setting the bias at minimum level, the pointer of
8b bias meter is still moved beyond the bias mark (about 1/3 between
the bias mark and the dot). The sound however is creamy and smooth and
all 4 KT66 are looked fine (tubes did not glow red).
My questions are:-
1) whether it is safe to use KT66 on M8b but how to set the bias
properly using the 8b's meter.
2) whether using KT66 would damage the 8b in long run (i.e. would KT66
put extra strain to my 8b?).
Please advise and thanks.

[l***@yahoo.com]

Where was your bias point when using GEC KT66 on your M8? The bias mark
or the dot or somewhere in between on the M8 meter?

[l***@yahoo.com]

anymore experts' opinion?

[Patrick Turner]

Post by l***@yahoo.com
anymore experts' opinion?

Just make damn sure that whatever you use as output tubes
does not allow the idle condition for plate and screen dissipation to be
more than
about 0.8 times the data for the tube.

Measure plate to cathode DCvoltage and anode current.
Then you have Ea and Ia.
If you have 400v and 45 mA, the product is the plate dissipation, and
should be less than
19 watts for EL34 and KT66.
400 x 0.045 = 18 watts = OK.

Then measure voltage from the screen to cathode anmd screen current.
You have Eg2, and Ig2.
Their product is the screen dissipation, and this should be less than
10% of the plate dissipation.

If KT88/6550 are used in liew of KT66/EL34, make sure
the Ea and Ia are the **same** as for the recomended EL34 set up
figures.

You may have to altern the bias circuit to allow correct biasing.

After correcly biasing, listen to the sound and enjoy,
but never run any output tubes at too high a bias current
regardless of how good it sounds unless you like teetering on the edge
of
expensive disasters.

Patrick Turner.

[l***@yahoo.com]

more opinion please.