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Old 3rd April 2012, 12:20 PM   #1
tim614 is offline tim614  United States
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Default Kt120 screen current

Kt120 I'n my PP UL amp draws 10ma on the screen, is this normal? kinda high compare to kt88.
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Old 3rd April 2012, 04:52 PM   #2
kevinkr is offline kevinkr  United States
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Provide plate voltage, operating point, and screen voltage and someone may be able to answer your question. Other circuit details like screen (UL, pentode) configuration and series resistance if any, and fixed/cathode bias, and OPT winding DCR if UL would also be useful.
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Old 3rd April 2012, 06:12 PM   #3
tim614 is offline tim614  United States
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Quote:
Originally Posted by kevinkr View Post
Provide plate voltage, operating point, and screen voltage and someone may be able to answer your question. Other circuit details like screen (UL, pentode) configuration and series resistance if any, and fixed/cathode bias, and OPT winding DCR if UL would also be useful.
Push-pull ultra linear with 1k inseries to the screen.
578v on plate
578v on screen before the 1k resister
568v on screen after 1k resister (10 volt drop across the 1k=10ma)
cathode bias @ 70ma per tube
5k OPT (Hammond 1650R)
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Old 3rd April 2012, 06:44 PM   #4
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Quote:
Originally Posted by tim614 View Post
568v on screen after 1k resister (10 volt drop across the 1k=10ma)
This means screen dissipation = 5.68 W. What's the maximum screen dissipation rating for this tube?

Best regards!
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Old 3rd April 2012, 06:49 PM   #5
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If the tube is a Tung-Sol, the maximum screen dissipation is 8 watts.
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Old 3rd April 2012, 07:06 PM   #6
tim614 is offline tim614  United States
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Quote:
Originally Posted by Frank Berry View Post
If the tube is a Tung-Sol, the maximum screen dissipation is 8 watts.
yes, Tungso kt120.
just want to make sure before i call this amp done
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Old 3rd April 2012, 07:11 PM   #7
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Enjoy the amp!
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Old 3rd April 2012, 07:13 PM   #8
tim614 is offline tim614  United States
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alright!
thanks guys.
i can wait till i get off work and do some listening.
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Old 3rd April 2012, 11:42 PM   #9
AJT is offline AJT  Philippines
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Quote:
Originally Posted by tim614 View Post
Push-pull ultra linear with 1k inseries to the screen.
578v on plate
578v on screen before the 1k resister
568v on screen after 1k resister (10 volt drop across the 1k=10ma)
cathode bias @ 70ma per tube
5k OPT (Hammond 1650R)

tube dissipation at 44.8watts.....would be interesting to find out full power B+...
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Old 3rd April 2012, 11:49 PM   #10
AJT is offline AJT  Philippines
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you may also want to try pentode operation with screens regulated at say 500volts......i find out that my 6LU8 pp amps give better bass than my EL34, 6P3C pp amps run ultra-linear....
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