Good points. I hadn't considered the continuous development of the 6L6. We're both in agreement on the Williamson's stability - that's why I restricted my recommendation to the output transformer, which is superb, or over-engineered, if you like.
KT66 choices
I have the Tingsol 6L6G and the Genelex KT66 in my SE amp.
They are both awesome and blow away the competion.
They are quite different though in presentation.
The KT66 is more dynamic and extended.
The 6L6G is more relaxed and intimate.
The KT66 is more of a concert front row center.
The 6L6G is more of a club sound filling the room.
The 6L6G is rated at the full 6L6GC voltage rating.
Both are in a coke bottle and are re-issues.
I use the 6L6Gs for jazz and easy listening.
I use the KT66s for the harder stuff like rock.
DanL
I have the Tingsol 6L6G and the Genelex KT66 in my SE amp.
They are both awesome and blow away the competion.
They are quite different though in presentation.
The KT66 is more dynamic and extended.
The 6L6G is more relaxed and intimate.
The KT66 is more of a concert front row center.
The 6L6G is more of a club sound filling the room.
The 6L6G is rated at the full 6L6GC voltage rating.
Both are in a coke bottle and are re-issues.
I use the 6L6Gs for jazz and easy listening.
I use the KT66s for the harder stuff like rock.
DanL
No, no, no, no...
The 6L6, 7581A, and all the variants of the 6L6 family are NOT suitable substitutes for nearly all KT66 PP Class AB1 amplifiers.
The output impedance is 8Kohms for a PP pair of KT66s and for all of the 6L6 family it is 5.6Kohms in the same configuration.
The only suitable substitute is the 6V6 which also has a output Z of 8Kohms in PP Class AB1 configurations. But, it is not always suitable because of bias voltage,plate voltage ranges, and dissipation 22Wavg vs. 33Wavg/pair.
Even the GE 7581A/KT66 labeled tubes are NOT suitable long term because of this impedance mis-match.
Please be careful out there...
The 6L6, 7581A, and all the variants of the 6L6 family are NOT suitable substitutes for nearly all KT66 PP Class AB1 amplifiers.
The output impedance is 8Kohms for a PP pair of KT66s and for all of the 6L6 family it is 5.6Kohms in the same configuration.
The only suitable substitute is the 6V6 which also has a output Z of 8Kohms in PP Class AB1 configurations. But, it is not always suitable because of bias voltage,plate voltage ranges, and dissipation 22Wavg vs. 33Wavg/pair.
Even the GE 7581A/KT66 labeled tubes are NOT suitable long term because of this impedance mis-match.
Please be careful out there...
There is one tube that fits the quadII : KT66
This tube is in current production and is available worldwide.
Have a look at Pat Turner's Quad II mods. Even the "Very Basic" (even without the bias monitoring circuit) looks like a good idea. Tubes? Maybe Genelex (Russian reissue) KT77? They might draw a bit more filament current but if you aren't using the II to power the Quad pre probably not a big deal.
S.
quad2powerampmods
S.
quad2powerampmods
Thread was dead for 12 years.
Power pentodes do not "have an impedance".
Most KT66 designs will eventually kill 6V6.