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Old 11th May 2012, 01:44 PM   #31
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Join Date: Apr 2009
Originally Posted by nigel pearson View Post
What about the Russian version GU 50 ? It is worth a look . It was what the Germans came up with about 1942 and think was called a Ray Pentode . Time is running out to buy these . Telefunken LS 50 and Chinese FU 50 also .

GU-50 - Wikipedia, the free encyclopedia

Check Wavebourn's posts at these pages; he is the GU50 specialist.
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Old 11th May 2012, 01:46 PM   #32
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Location: Oxfordshire
ECC 81 and EF184 are not often thought of to drive KT88 ( 6550 ) . They are possible options . EF184 in Long tail pair perhaps . I don't get involved in PP so out of my depth after that . Look at Quad 11 and see if it can be scaled up . Over to someone who would know on that .

I am looking to buy some KT 88 . I don't want to pay silly money and would use EL156 if I did . JJ is out I think .


Last edited by nigel pearson; 11th May 2012 at 02:13 PM.
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Old 11th May 2012, 02:19 PM   #33
limono is offline limono  United States
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New Quad II forty by TdP which I was checking after it was blowing tubes runs them at 390-400V 100mA in cathode bias circuit . You need Penta Labs Kt88's with ~50W dissipation rate to run in High Power Circuit. Don't forget to confront your design with well regarded circuits. Personally I'd try Allen Wright (may he rest in peace) PP-2 amp.
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Old 11th May 2012, 02:23 PM   #34
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I think 400 V and 70 mA wise ?
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Old 11th May 2012, 02:28 PM   #35
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Penta labs KT 88 . Thanks . The plate dissipation is exactly what I wanted to know .

Modern Penta Lab KT88 Vacuum tube.MOV - YouTube
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Old 12th May 2012, 12:52 PM   #36
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Default KT 88 tester

Click the image to open in full size.

I think this would work OK as a tester ? In a wood or plastic enclosure as it is not isolated . Various valves could be tested and data kept .

For USA I guess a capacitor fed doubler would give the same ?

Put a high grade input signal transformer on it and you would have an amplifier . Safety will be OK then if careful . NE 5534 op amp or boosted OPA 604 would drive it . I have tried something like this in the past built for me by my brother . I felt a mains transformer offered advantages sonically .

The 6V is a switch mode PSU for simplicity ( 6.3 V ) . The -6V bias switch is to lower the KT 88 into a lower bias . That would I guess make an ideal standby switch if an ideal voltage was found ( run from a comparator perhaps with a 1 hour flip flop action ) ? Please improve this idea if you can .

Stontronics 6V 2A Desktop Power Supply Unit T2319ST
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Old 12th May 2012, 03:34 PM   #37
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Default Sid Smiths circuit for Marantz 7 C and others

I was asked for this . As far as I know this was originated by Sid . I have heard it and it is good . Remember back then LM317 was very exciting .

DIY Test Equipment for Audio and Ham Radio Enthusiasts


Last edited by nigel pearson; 12th May 2012 at 03:49 PM.
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