quads11&22 back into service

solderon · 27th September 2011, 08:29 PM

i have had this combination in a cupboard for several years whilst i used my leak st20.Now i intend to bring it into service using a variac.Should i connect both the quad11 to the 22,or only connect one at atime.The only load i have at this time is apair of jr 149s.also the kt66s inthe amp are not of the best quality and would like to replace them.the old gec etc valves are far to exspensive and the new ones dont realy get recommended.On some other forums they recomend 6l6gcs,5881.Are these tubes a straight replacement for the kt66.I would welcome any advice you can offer.
best wishes.

carbondated · 27th September 2011, 09:24 PM

No, they're not. They will work, but in the long term may screw up the amp unless you change the internals (the common cathode to ~240R) - in which case it wouldn't be a Quad II. I believe the modern production Quad Classics use Tung-Sol valves.

The caveat to this is that modern KT66s aren't terribly standardised, and a lot of the other components inside may have drifted as well, so the difference might turn out to be negligible all things considered.

kevinkr · 27th September 2011, 09:25 PM

Each one separately and you should monitor the supply voltages so that you know immediately that something has gone wrong. A ballast lamp is not a bad idea in the event that a cap shorts out, the lamp will prevent sufficient current from being drawn to fry the power transformer..

The ballast lamp is just a bulb in series with the load.. Could be 100W or so to start..

The 7581 is a direct replacement for the KT66, unfortunately it is now rare and expensive, the 6L6GC should be fine as well, the 5881 should work but some modern examples are a bit questionable dissipation wise compared to NOS.. There are some reasonably OK KT66 knock offs from New Sensor and China manufacturers as well. Most modern tubes are not that great frankly.. Just get yours tested, burned in and matched..

johnm · 29th September 2011, 10:32 PM

Just to add to the list of valve subs, the original Quad manual states that 6L6G or 5883 valves can be used instead of KT66s.

Best of luck with it all - I'm just restoring my pair and can't wait to get them up and running again

27th September 2011, 08:29 PM	#1
solderon diyAudio Member Join Date: Sep 2010	quads11&22 back into service i have had this combination in a cupboard for several years whilst i used my leak st20.Now i intend to bring it into service using a variac.Should i connect both the quad11 to the 22,or only connect one at atime.The only load i have at this time is apair of jr 149s.also the kt66s inthe amp are not of the best quality and would like to replace them.the old gec etc valves are far to exspensive and the new ones dont realy get recommended.On some other forums they recomend 6l6gcs,5881.Are these tubes a straight replacement for the kt66.I would welcome any advice you can offer. best wishes.

27th September 2011, 09:25 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Each one separately and you should monitor the supply voltages so that you know immediately that something has gone wrong. A ballast lamp is not a bad idea in the event that a cap shorts out, the lamp will prevent sufficient current from being drawn to fry the power transformer.. The ballast lamp is just a bulb in series with the load.. Could be 100W or so to start.. The 7581 is a direct replacement for the KT66, unfortunately it is now rare and expensive, the 6L6GC should be fine as well, the 5881 should work but some modern examples are a bit questionable dissipation wise compared to NOS.. There are some reasonably OK KT66 knock offs from New Sensor and China manufacturers as well. Most modern tubes are not that great frankly.. Just get yours tested, burned in and matched.. __________________ www.kta-hifi.net

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27th September 2011, 09:24 PM	#2
carbondated diyAudio Member Join Date: Jan 2011	No, they're not. They will work, but in the long term may screw up the amp unless you change the internals (the common cathode to ~240R) - in which case it wouldn't be a Quad II. I believe the modern production Quad Classics use Tung-Sol valves. The caveat to this is that modern KT66s aren't terribly standardised, and a lot of the other components inside may have drifted as well, so the difference might turn out to be negligible all things considered.

29th September 2011, 10:32 PM	#4
johnm diyAudio Member Join Date: Sep 2003 Location: Hampshire	Just to add to the list of valve subs, the original Quad manual states that 6L6G or 5883 valves can be used instead of KT66s. Best of luck with it all - I'm just restoring my pair and can't wait to get them up and running again

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