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Old 12th November 2014, 12:42 PM   #1
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Default Little OTL / Class " A "

hello ,

i test the build to OTL / Class A to EL 504 ( up EL 502 or 6P45s ) .

the power in build is small , +/- 600 mW to 8 Ohms .

i joint the schéma and pictures to build to test .

and sound for the test 2 EL 502 for 1 Way ( 1 triode ECC 83 )

Test Prototype OTL - Music Freddie Mercury - Vidéo Dailymotion

nice sound for very small build ( and big consumer energy ) ...

tk , good day for all
Attached Images
File Type: jpg OTL_Asymtric_EL 504.jpg (173.7 KB, 340 views)
File Type: jpg Alim OTL_Asymtric_EL 504 - 170 V=.jpg (186.8 KB, 329 views)
File Type: jpg OTL - 160 V=.JPG (251.3 KB, 314 views)
File Type: jpg PICT6565.JPG (225.0 KB, 307 views)
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Old 12th November 2014, 01:31 PM   #2
Bigun is online now Bigun  Canada
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Looks fun!
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 12th November 2014, 04:05 PM   #3
TheGimp is offline TheGimp  United States
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I think you need some form of negative bias for the grid (G1). As drawn the only bias for the tubes will be due to the 25R resistance of the choke L1.

With 170V B+ to bias the tubes at 70% dissipation, you need about -24V of bias.

Without this the tubes will run very hot (red plate) and suffer short life.

Be aware that the output on the top of the inductor can go negative if the amp is driven hard enough, resulting in reverse bias on the output capacitor(C2).
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Old 12th November 2014, 05:54 PM   #4
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Hello TheGimp ,

the L1 is up to 56 Ohms approximatly and the power is 160 V= +/- 5V=

the all's tubes ( EL 504 or EL 502 and maximum EL 509 / 6P45S ) is adjoint small résistor to equal ( +/- 1 Ohms ) to série at inductance to 56 Ohms .

the test in prototype to 2 EL 502 use 1 Hour is good , not red plate

tk for help
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Unread Today, 04:26 AM   #5
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hello , i continous test to me prototype build ...

i tested the stéréo to 1 EL 519 for 2 Ways and 1 drive ECC82

+/- 500 mW to 160 V= and +/- 200 mA to 1 way ( the résistor for bias is 89 Ohms )

good day for all
Attached Images
File Type: jpg OTL 2 X EL 519 and 1 ECC 82.JPG (256.0 KB, 91 views)
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