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Old 8th February 2003, 10:07 PM   #1
Aiace is offline Aiace  Italy
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Lightbulb SEPP for philips 800 ohm loudspeaker

I'm going to build a SEPP with EL86 to drive a 800 ohm Philips speaker. The schematic is close the original Philips but I use tube as triode. My project is correct? there are some advice for me?
Thank you
Aiace
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Old 9th February 2003, 12:01 AM   #2
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Hi

This circuit can only work in class A and power with the tubes pentode connected will be quite low ~ 4.5W with 300V B+ according to Philips, the screen grid of the upper tube is bootstrapped in the Philips original circuit so that the screen to cathode potential is constant over the signal envelope.

Using the tubes triode connected I would expect the power to be even lower at the same B+ voltage.

By using an ordinary phase splitter to drive the grid of each tube it is possible to operate in class AB and increase power up to ~14W, I have an old magazine article describing such an amplifier as DIY project pushing out 12W at 0.08% distorsion and frequency range flat up to 200kHz.

Regards Hans
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Old 9th February 2003, 12:16 AM   #3
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Default PHILIPS OTL

Hi,

Quote:
By using an ordinary phase splitter to drive the grid of each tube it is possible to operate in class AB and increase power up to ~14W, I have an old magazine article describing such an amplifier as DIY project pushing out 12W at 0.08% distorsion and frequency range flat up to 200kHz.
Indeed,and it sounded not bad at all...running the same topyloge from trioded EL86/6CW5s would be O.K. for a headphone set or extremely effecient speakers....where I would opt for a different approach any way.

If you insist on a triode output using this topology (SEPP), then there a number of very linear regulator tubes out there that ar far more apt for the job.

Candidates are the 6AS7G Sovtek,6C19P,6C41,6C33-C or the NOS 6528,6336A and no doubt some others.

Although I never had the chance to listen the Philips OTL + 800 R speaker combo (AD9710?) I had the OTL from Philips at one time and even with a Zo of 800 Ohm it drove my 8 Ohm speakers remarkably well.
Both through the cap or the 1:1 transformer.

I haven't had a good look at you circuit yet but if I find a fault I'll let you know.

Cheers,

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Frank
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Old 10th February 2003, 08:20 PM   #4
316a is offline 316a  England
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Default SEPP

Hello ,
Frank is right suggesting to go the low Ra route . I am using a transformer coupled SEPP with stacked 6C33 at present and it works rather well . EL86 used in the original design strapped as triodes may not be beefy enough in this circuit

316a
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